oversaw the preparation of this document. WHO acknowledges the technical contributions of the following individuals#
The most susceptible group for iodine deficiency disorders is women of reproductive age, whose neonates, if iodine deficient in utero, are at high risk of irreversible mental impairment. Moreover, the other susceptible group is women providing breast milk to their children, as this may be the only source of iodine during the first 6 months of life. It is estimated that about 1.88 billion people worldwide remain at risk of insufficient iodine intake, if iodine interventions are not kept in place. Approximately one third of the world's population lives in areas where natural sources of iodine are low, and therefore they require the permanent presence of iodine-supplying interventions. This population at risk of iodine deficiency is unevenly distributed across the world and within countries.
Salt iodization is the preferred strategy for control of iodine deficiency disorders and is implemented in more than 120 countries around the world. Many countries worldwide have successfully eliminated iodine deficiency disorders or made substantial progress in their control, largely as a result of salt iodization.
Salt is considered an appropriate vehicle for fortification with iodine, for the following reasons: (i) it is widely consumed by virtually all population groups in all countries, with little seasonal variation in consumption patterns, and salt intake is proportional to energy intake/requirements; (ii) in many countries, salt production is limited to a few centres, facilitating quality control; (iii) the technology needed for salt iodization is well established, inexpensive and relatively easy to transfer to countries around the world; (iv) addition of iodate or iodide to salt does not affect the taste or smell of the salt or foods containing iodized salt, and therefore consumer acceptability is high; (v) iodine (mainly from iodate) remains in processed foods that contain salt as a main ingredient, such as bouillon cubes, condiments and powder soups, and hence these products become sources of iodine; and (vi) iodization is inexpensive (the cost of salt iodization per year is estimated at US$ 0.02-0.05 per individual covered, and even less for established salt-iodization programmes). Additionally, the concentration of iodine in salt can easily be adjusted to meet policies aimed at reducing the consumption of salt in order to prevent cardiovascular disease.
Considering the existing World Health Organization (WHO) policies about reducing the intake of salt and delivering adequate dietary iodine to populations, it is important to establish the amount of iodine in salt that would provide sufficient iodine for salt intakes of <5 g/day. Iodization methods can provide the recommended concentrations of iodine for this amount of salt intake, so these two policies are compatible. However, careful monitoring of fortification procedures and salt iodine levels is therefore of paramount importance.
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 2

# Purpose of the guideline
The proposed guideline 1 aims to help Member States and their partners in their efforts to make informed decisions on the appropriate nutrition actions to achieve the Millennium Development Goals (MDGs), in particular, reduction of child mortality (MDG 4) and improvement of maternal health (MDG 5). It will also support Member States in their efforts to achieve global targets on the Comprehensive implementation plan on maternal, infant and young child nutrition and in the Global action plan for the prevention and control of noncommunicable diseases 2013-2020, as approved in resolution WHA66.10 in 2013, including the voluntary global targets on salt reduction. This guideline is intended for a wide audience, including policy-makers; their expert advisers; and technical and programme staff at organizations involved in the design, implementation and scaling-up of salt-iodization programmes, and in nutrition actions for public health. Engagement and commitment of the private sector can benefit fortification efforts and the implementation process.

# Guideline development methodology
WHO developed the present evidence-informed recommendations using the procedures outlined in the WHO handbook for guideline development. The steps in this process included: (i) identification of priority questions and outcomes; (ii) retrieval of the evidence; (iii) assessment and synthesis of the evidence; (iv) formulation of recommendations, including research priorities; and (v) planning for dissemination, implementation, impact evaluation and updating of the guideline. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology was followed, to prepare evidence profiles related to preselected topics, based on up-todate systematic reviews.
The guideline development group -nutrition actions 2013-2014 consisted of content experts, methodologists, and representatives of potential stakeholders and consumers. One expert group participated in the WHO technical consultations concerning this guideline, held in Geneva, Switzerland on 20-25 February 2010, where the guideline was scoped. A second meeting was convened with the guideline development group -nutrition actions 2013-2014 in Geneva, Switzerland on June 23-26 2014. A consultation in Sydney, Australia, in March 2013 about strategies to reduce salt/sodium intake at the population level, while ensuring adequate iodine nutrition, was also assessed.
Members of the external review group were identified through a public call for comments, and this panel was involved throughout the guideline development process. The document was peer-reviewed by six experts, who provided technical feedback on the document.

# Available evidence
The available evidence comprised a systematic review that followed the procedures of the Cochrane handbook for systematic reviews of interventions and assessed the effects and safety of fortification of food-grade salt with iodine. The review included randomized controlled trials, non-randomized controlled trials and quasi-experimental, cohort and multiple cross-sectional studies. All studies compared a group of individuals with exposure to iodized salt to a group without exposure to iodized salt. The review included two randomized controlled trials, six non-randomized controlled trials and 20 quasi-experimental, 16 cohort and 42 multiple cross-sectional studies, as well as three studies with mixed designs. Another review assessed whether there were alternative food vehicles fortified with iodine to prevent iodine deficiency disorders. The overall quality of the available evidence for salt fortification with iodine ranged from moderate to low for the critical outcomes of goitre (moderate), cretinism (moderate), low cognitive function (low) and urinary iodine concentration (moderate).
All food-grade salt, used in household and food processing, should be fortified with iodine as a safe and effective strategy for the prevention and control of iodine deficiency disorders in populations living in stable and emergency settings (strong recommendation).
Suggested concentrations for fortification are shown in Table 1.
- This recommendation recognize that salt reduction and salt iodization are compatible. Monitoring of sodium (salt) intake and iodine intake at country level is needed to adjust salt iodization over time as necessary, depending on observed salt intake in the population, to ensure that individuals consume sufficient iodine despite reduction of salt intake).
The concentrations of iodine may need to be adjusted by national authorities responsible for the implementation and monitoring of universal salt iodization, in light of their own data regarding dietary salt intake.
The national distribution of salt consumption must provide key guidance for the concentration of iodine in salt ; sufficient iodine should be supplied to most members of the population, even those with the lowest salt intake, while at the same time preventing excessive iodine supply to those individuals whose salt intake remains high.
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 4
- Iodized salt should reach, and be used by, all members of the population after 1 year of age. Infants and young children are assumed to be covered via breast milk or iodine-enriched infant formula milk when this is prescribed. Addition of salt to products consumed by young children may need regulation, to avoid insufficient or excessive consumption of either sodium (salt) or iodine.
- Since pregnant women have a daily iodine requirement of 250 g/day, other interventions such as iodine supplementation could be considered if iodine inadequacy is found. Intake of salt correlates with caloric intake, and pregnant women usually increase their energy intake during this physiological stage.
- Policies for salt iodization and reduction of salt to <5 g/day are compatible, cost effective and of great public health benefit. Although salt is an appropriate vehicle for iodine fortification, iodization of salt should not justify promotion of salt intake to the public.
- Monitoring of food-grade salt quality is essential to ensure both efficacy and safety of the process of iodine fortification. Monitoring of urinary iodine excretion (UIE) and urinary iodine concentration (UIC) is useful not only to detect deficiency but also to detect excessive intakes and therefore prevent the health risks of iodine excess, by adjusting the level of iodine fortification accordingly, as part of a monitoring system. Countries should determine iodine losses from iodized salt under local conditions of production, climate, packaging and storage. For these reasons, iodine losses may be extremely variable and influence the additional amount of iodine that should be added at factory level.
- Fortification of salt with iodine should be appropriately regulated by governments and harmonized with other local or country programmes, to ensure that fortified food-grade salt is delivered safely within the acceptable dosage range. Particular attention should be given to identifying potential barriers to equitable access for all population groups needing iodine-fortified salt.
- Country programmes should be culturally appropriate to the target populations, so the intervention is accepted, adopted and sustained.
- Clear legislation should also be established for food producers and distributors, especially where the main source of dietary salt is processed foods and meals consumed outside households. Legislation should cover not only proper iodization of salt, but also the salt content of industrialized food products.
- Establishment of an efficient system for the ongoing and routine collection of relevant data, including measures of quality assurance and household use of iodized salt and measures of programme performance, is critical to ensure programmes for iodized salt are effective and sustained. 1 Aburto NJ, Abudou M, Candeias V, Wu T. Effect and safety of salt iodisation to prevent iodine deficiency disorders: a systematic review with meta-analyses. 2014; (in press). 2 The Salt Institute. Iodized salt (/, accessed 10 September 2014). b This fortification concentration was calculated based on the mean recommended nutrient intake of 150 g iodine/day + 30% losses from production to household level before consumption, and a 92% iodine bioavailability. Losses depend on the iodization process, the quality of salt and packaging materials and the climatic conditions. Losses could vary widely 1 and this table presents the value considering 30% losses. The monitoring of urinary iodine concentrations will allow adjustment of the selected fortification concentrations. RNI: recommended nutrient intake, is the daily intake, set at the estimated average requirement plus 2 standard deviations, which meets the nutrient requirements of almost all apparently healthy individuals in an age-and sex-specific population group.

# Estimated salt consumption
Although iodate is more stable, either potassium iodate (KIO 3 or iodide (KI) can be used. Iodide may be used for dry, low crystal size and washed or refined salts. While iodate can be used alone and in any type of salt quality, iodide is used in very good quality salt and cannot be added alone. Therefore, some salt producers add sodium carbonate or sodium bicarbonate when they iodize salt, to increase alkalinity, and sodium thiosulfate or dextrose to stabilize potassium iodide. Without a stabilizer, potassium iodide may be oxidized to iodine and lost by volatilization from the product. 2 An estimated additional variability of 10% during iodization procedures could be considered at the production site for use in quality control and assurance procedures. This variability depends on the iodization methods used and quality assurance system in place.
Shaded areas correspond to the WHO salt reduction guideline. Table 1. Suggested concentrations for the fortification of food-grade salt with iodine.
- Regular monitoring and evaluation can identify barriers that may be limiting equal access to fortified salt and thus preserving health inequities. Sustained implementation and scale-up derive great benefit from appropriate monitoring mechanisms.
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 6

# Implications for future research
Discussions with members of the WHO guideline development group and the external review group highlighted the limited evidence available in some areas, meriting further research on the fortification of food-grade salt with iodine, in particular in the following areas:
- determination of the relationships between iodine excretion (24-h collection) and UIC in different ages, sexes, and physiological stages (mainly pregnancy and lactation), and under different climatic conditions and levels of physical activity, in order to adjust the criteria for UIC for population assessments;
- determination of the relative contribution to iodine intake from table salt and from processed foods;
- investigation of the usefulness of thyroglobulin as a functional indicator of iodine status, to complement the use of UIC as an indicator of iodine intake;
- investigation of whether iodine deficiency (mild or moderate) is occurring in pregnant and lactating women worldwide, and the potential negative impact in their health, as well as on development of their offspring;
- alignment of national salt-iodization and dietary salt-reduction programmes, including optimization of policy implementation and ensuring effective monitoring and coordination of monitoring; 6. understanding the potential impact of salt-containing processed foods, such as bouillon cubes, condiments and powder soups, and other edible vehicles;
- identification of the optimal indicators to assess iodine nutrition during pregnancy, lactation and infancy. The use of neonatal serum concentration of thyroid-stimulating hormone as an indicator of iodine status in pregnancy needs further validation;
- better prevalence data on the iodine status of pregnant and lactating women, and infants; 9. more data from large studies of the impact of iodine-intervention programmes on iodine-induced thyroiditis and iodine-induced hyperthyroidism;
- further studies to correct misperceptions that link iodized salt to certain diseases, as well as the barriers that might be encountered during implementation and scale-up, such as consumer demand for non-iodized salt, religious concerns relating to iodized salt, and the perception of extra costs of purchasing iodized salt. Findings arising from these studies can help identify bottlenecks and barriers to access to iodine-fortified food-grade salt;
- studies to identify the knowledge and awareness of the general population about the use of iodized salt are important to address barriers such as religious concerns and existing demand for non-iodized salt;
- studies to search and evaluate the use of different vehicles for iodine fortification.

# Scope and purpose
This guideline provides global, evidence-informed recommendations on fortification of food-grade salt with iodine, for the prevention and control of iodine deficiency disorders, with the purpose of improving iodine nutrition and preventing iodine deficiency disorders in populations.
The guideline will help Member States and their partners in their efforts to make informed decisions on the appropriate nutrition actions to achieve the Millennium Development Goals (MDGs), in particular reduction of child mortality (MDG 4) and improvement of maternal health (MDG 5). It will also support Member States in their efforts to achieve global targets of the Comprehensive implementation plan on maternal, infant and young child nutrition, as endorsed by the Sixty-fifth World Health Assembly in 2012, in resolution WHA65.6 (1), and in the Global action plan for the prevention and control of noncommunicable diseases 2013-2020 (2), as approved in resolution WHA66.10 in 2013, including the voluntary global targets on salt reduction (3).
The guideline is intended for a wide audience, including policy-makers; their expert advisers; and technical and programme staff at organizations involved in the design, implementation and scaling-up of salt-iodization programmes, and in nutrition actions for public health. This document presents the key recommendations and a summary of the supporting evidence. Further details of the evidence base are provided in Annex 1 and other documents listed in the references.
Iodine is a trace element that is essential for the synthesis of thyroid hormones by the thyroid gland. These hormones are involved in growth, development and control of metabolic processes in the body. The iodine content of foods depends on the iodine content in the soil. Thus, low iodine concentrations in soil and water result in iodinedeficient plants and animals (4). As populations depend on food sources grown in areas where iodine may be deficient, iodine can only enter the food supply through the addition of this nutrient to nutrient-delivery interventions, and the most common has been a common staple: edible food-grade salt, a crystalline product consisting predominantly of sodium chloride (5).
The most susceptible group for iodine deficiency disorder is women of reproductive age, whose neonates, if iodine deficient in utero, are at high risk of irreversible mental impairment. Moreover, the other susceptible group is women providing breast milk to their children, as this may be the only source of iodine for an infant during the first 6 months of life (4). It is estimated that about 1.88 billion people worldwide are at risk of insufficient iodine intake if iodine-delivered interventions are not kept in place (4). Approximately one third of the world's population lives in areas where natural sources of iodine are low, and therefore they require the permanent presence of iodine-supplying interventions. Approximately 29.8% (241 million) school-age children globally are estimated to have insufficient intake of iodine.
Many of these 241 million children live in the World Health Organization (WHO) South-East Asia Region (76 million) and African Region (58 million) (6).
Salt iodization is the preferred strategy for control of iodine deficiency disorders and is implemented in more than 120 countries around the world (7). Many countries worldwide have successfully eliminated iodine deficiency disorders or made substantial progress in their control, largely as a result of salt iodization and dietary diversification. Dairy products are also a good source of iodine if cattle are fed with iodine-enriched feed, and therefore including milk and other dairy products as part of promotion of dietary diversification is important to prevent iodine deficiency disorders.
The most visible sign of iodine deficiency is goitre, an enlargement of the thyroid gland. Individuals living in areas affected by severe iodine deficiency may have an intelligence quotient (IQ) of up to 13.5 points below that of those from comparable communities in areas where there is no iodine deficiency (8-10).
When iodine intake is inadequate, the thyroid gland may no longer be able to synthesize sufficient amounts of thyroid hormones. Low levels of thyroid hormones in the blood, referred to as hypothyroidism, are responsible for damage to the developing brain and for the whole spectrum of iodine deficiency disorders. The spectrum of iodine deficiency disorders includes goitre; hypothyroidism; increased susceptibility to nuclear radiation; spontaneous abortion; stillbirths; congenital anomalies; perinatal mortality; endemic cretinism, including mental deficiency with a mixture of mutism, spastic dysplegia, squint, hypothyroidism and short stature; infant mortality; impaired mental function; delayed physical development; and iodine-induced hyperthyroidism (11,12). These can be prevented by ensuring that the population has an adequate intake of iodine.
Both insufficient and excess iodine can have negative effects on thyroid functioning. Excessive intake of iodine may be associated with complications such as iodine-induced hyperthyroidism in some cases (13) or hypothyroidism in others (14). Data indicate a small increase in the risk for iodine-induced hyperthyroidism with increasing iodine intakes in older adults, mainly those with pre-existing nodular goitre (14,15).
On a population basis, iodine-induced hyperthyroidism represents a transient increase in the incidence of hyperthyroidism that occurs when there is an increase in iodine intake in severely iodine-deficient populations. The number of people at risk of iodine-induced hyperthyroidism is directly proportional to the number of individuals with nodular goitre. This condition will disappear with the correction of iodine deficiency (16,17).
Based on studies of balance and excretion, an adult iodine intake is in the range of 100-300 g/day. The recommended daily intake of iodine is 90 g/day for infants and children aged less than 6 years, 120 g/day for children aged 6-12 years, and 150 g/day for adolescents and adults from 13 years of age through to adulthood. It is recommended that pregnant and lactating women consume 250 g of iodine per day (11). Sea fish and some seaweeds are good sources of dietary iodine. Iodine can also be found in vegetables and cereals if they are produced in iodine-sufficient soils, poultry or meat and milk, if the animals consume foods grown in iodine-sufficient soils or are given iodine-containing feed supplements. At all intake levels, a proportionate amount of iodine is excreted in the urine, so the urinary iodine excretion (UIE) using 24-h urine collections is the ideal biochemical indicator for assessing iodine status. However, owing to the difficulties associated with using this indicator for assessing populations and monitoring programmes, the simple urinary iodine concentration (UIC) has been used (18), although this may not reflect the intake distribution of individuals and populations as well as measurement of 24-h UIE.
Both UIC and UIE correlate with recent iodine intakes and, therefore, they are useful for estimating iodine intake. Currently, the median value of 100 g/L for UIC is being used to identify when an adult population has sufficient intake of iodine (19), but it has mainly been applied to school-age children, from whom is easier to collect urine samples (4). However, because of the lower urinary volume in children, the UIC may be higher in that age group than in adults. As of 2013, there were 57 million school-age children who were not attending school (20), which may affect the interpretation of the results. For pregnant women, however, a median UIC of <150 g/L has been proposed to indicate insufficient iodine intake (21).
In the past, the prevalence of goitre was also a commonly used indicator for the assessment of iodine deficiency in a population, although it has little practical usefulness now because goitre has nearly disappeared in many countries. Goitre is also not recommended for assessing the response to an intervention, as it can take months or years for goitre to regress after the normalization of iodine intake (11,22). However, it remains useful in countries or regions that have not yet introduced iodised salt programmes.
The concentrations of thyroid-stimulating hormone (TSH) and thyroid hormone (T 3 and T 4 in serum/plasma are additional indicators of iodine status. However, these indicators are usually not recommended for monitoring iodine nutrition, because they are more expensive and less sensitive (11). Measurement of serum or dried blood spot thyroglobulin (Tg) in school-age children appears to be a sensitive indicator of iodine status in a population and it may be used to monitor improving thyroid function after iodine repletion (11). However, further validation is required for standardization of collection and measurement techniques for Tg, and for establishment and interpretation of cut-off values (21).
Recognizing the importance of preventing iodine deficiency disorders, in 1991 the World Health Assembly adopted the goal of eliminating iodine deficiency as a public health problem. In 1990, world leaders endorsed this goal when they met at the World Summit for Children at the United Nations, and it was reaffirmed by the International Conference on Nutrition in 1992 (23). In 1993, WHO and the United Nations Children's Fund (UNICEF) recommended universal salt iodization as the main strategy to achieve elimination of iodine deficiency disorders (24). In 2005, the importance of eliminating iodine deficiency disorders was again recognized when the World Health Assembly adopted a resolution committing to reporting on the global situation of iodine deficiency disorders every 3 years (25). In 2013, the World Health Assembly further recognized that the fight against iodine deficiency disorders contributes directly to many of the MDGs, including anti-poverty, reduction of infant mortality, maternal health, education for all, gender equity and private-public partnership (26).
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 10

# Universal salt iodization
Since 1993, when WHO and UNICEF recommended universal salt iodization, many countries worldwide have made substantial progress in the control and prevention of iodine deficiency disorders, largely as a result of salt iodization. Salt iodization has been implemented in more than 120 countries around the world (27) and 71% of households worldwide are estimated to have access to adequately iodized salt (28). However, iodine deficiency disorders still constitute a public health problem in many countries where the salt iodization programmes are weakly implemented. On the other hand, it is important to avoid excess iodine fortification levels. Eleven countries have populations with apparent excessive iodine intakes based on UIC (6); however, the true iodine intake has not been assessed in most of them. Such excess intakes, if they exist, may be mainly due to excess fortification levels rather than excess salt intake.
Salt is considered an appropriate vehicle for fortification with iodine, for the following reasons: (i) it is widely consumed by virtually all population groups in all countries, with little seasonal variation in consumption patterns, and salt intake is proportional to energy intake/ requirements; (ii) in many countries, salt production is limited to a few centres, facilitating quality control; (iii) the technology needed for salt iodization is well established, inexpensive and relatively easy to transfer to countries around the world; (iv) addition of iodate or iodide to salt does not affect the taste or smell of the salt or foods containing iodized salt, and therefore consumer acceptability is high; (v) iodine (mainly from iodate) remains in processed foods that contain salt as a main ingredient, such as bouillon cubes, condiments and powder soups, and hence these products become sources of iodine; and (vi) iodization is inexpensive (the cost of salt iodization per year is estimated at US$ 0.02-0.05 per individual covered, and even less for established salt-iodization programmes) (12). Additionally, the concentration of iodine in salt can easily be adjusted to meet policies aimed at reducing the consumption of salt in order to prevent cardiovascular disease (29,30).
The amount of iodine added to salt should be based on the estimated daily consumption of salt. Salt is the main dietary source of sodium and a high intake of sodium has been associated with hypertension, cardiovascular disease and stroke; and decreasing sodium intake may reduce blood pressure and the risk of associated noncommunicable diseases. Salt consumption varies widely in different countries and sometimes within a country. For instance, some indigenous populations of Brazil have salt intakes of less than 1 g/day, while some countries like Korea or Japan have reported consumptions close to 20 g/day (31,32).
Since decreased sodium intake in the population is a cost-effective public health intervention that could potentially reduce morbidity and mortality associated with noncommunicable diseases, and because of the increasing importance of noncommunicable diseases for health-care costs and burden of disease, WHO recently updated guidance on sodium intake for adults and children (33). WHO currently recommends a reduction to <2 g/day sodium (5 g/day salt) in adults, and in children the recommended maximum level of intake should be adjusted downward based on the energy requirements of children relative to those of adults. This applies to all individuals, with or without hypertension, and should be complemented with the WHO guideline on potassium intake and other nutrient guidelines and recommendations, to guide the development of public health nutrition programmes and policies (34)(35)(36).
It has been recognized that polices on salt reduction and salt iodization are compatible (29,30). Monitoring of salt intake and salt iodization at country level is needed to adjust salt iodization over time as necessary, depending on observed salt intake in the population, to ensure that individuals consuming the recommended amount of sodium continue to consume sufficient iodine. Resolution WHA57.17 on the Global strategy on diet, physical activity and health (37) confirmed that the policy on salt iodization for preventing iodine deficiency should be compatible with the recommendation to limit salt (sodium) consumption from all sources.
Although WHO recommends a reduction in the intake of salt to less than 5 g/day, on average, it is estimated that individuals still consume around 10 g of salt per day in countries where most of the salt in the diet comes from household salt, used for home cooking and at the table (36). Previous estimations assumed an average salt intake of 10 g per capita per day, and recommended that salt be iodized at a concentration of 20 mg iodine per kg of salt. The minimum and maximum levels used for the iodization of food-grade salt (expressed as mg iodine/kg salt) needed to be established by the national health authorities in the light of the local iodine deficiency situation, local consumption of salt and quality systems in place.
Although universal salt iodization calls for fortification with iodine of all food-grade salt for human and animal consumption, including salt for food processing, in practice, focus on implementation had only been on table salt and not on all salt destined for the food industry or animal consumption. Food-grade salt can obtained from the sea, from underground rock salt deposits or from natural brine (5). Washed and refined salt is the most widely used form. The main bulk of salt is sold for industrial use, where it has great commercial value as a necessary ingredient in many manufacturing processes.
Recent trends, particularly in high-income and middle-income countries, but also urban populations in low and middle income countries, show that individuals are consuming the majority of their salt through processed foods, in which iodized salt is generally not used, rather than through iodized salt. Nevertheless, in many low-and middle-income countries, discretionary salt (cooking and table) continues to be the main source of salt (29). Thus, countries that focus on iodization of table salt alone may not achieve optimal iodine nutrition of their population (38) and it is necessary to include iodized salt in processed foods.
There have been some concerns about technical difficulties, retention, losses and changes in organoleptic properties of final products, with the inclusion of iodized salt in industrialized processed foods (39,40). However, studies in more than 20 food products containing salt fortified with potassium iodide or potassium iodate found no adverse effects on food quality (39,41). Concerns still remain regarding the stability of iodine during food processing (42) and supply of iodine through these sources remain uncertain, although products with high content of salt, such as bouillon cubes, condiments and powder soups made with iodized salt, retain the iodine after production. It has been reported that considerable losses, up to 100%, are possible during food processing, depending on the product and the procedure, moisture, heating and storage (43)(44)(45)(46)(47)(48).
Successful and sustainable implementation of the use of iodized salt in processed foods requires awareness of the risks of iodine deficiency, adequate legislation in line with a country's dietary customs and "legislation culture", regular monitoring of iodine nutrition status and dietary intake, and a cooperative role of the salt industry and food processors (39).

# Summary of evidence
A systematic review that followed the procedures of the Cochrane handbook for systematic reviews of interventions (49) was prepared, on the use of iodized salt for preventing iodine deficiency disorders (50). This updated review considers the recent efforts to reduce the overall consumption of salt in populations. Comparisons were made between the consumption of iodized salt and a placebo, non-iodized salt or no intervention.. The results also indicate that, in some contexts, iodization of salt at the population level may cause a transient increase in the population incidence of hyperthyroidism, but not hypothyroidism. However, the beneficial effects of iodization of salt far outweigh the potential adverse effects. The quality of evidence for salt fortification with iodine ranged from moderate to low for the critical outcomes of goitre (moderate), cretinism (moderate), low cognitive function (low) and urinary iodine concentration (moderate), using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology (52).
This guideline supersedes previous WHO recommendations on salt iodization (11,16,18).
All food-grade salt, used in household and food processing should be fortified with iodine as a safe and effective strategy for the prevention and control of iodine deficiency disorders in populations living in stable and emergency settings (strong recommendation). 1 Suggested concentrations for the fortification of food-grade salt with iodine are shown in Table 1.
Table 1. Suggested concentrations for the fortification of food-grade salt with iodine. 1 A strong recommendation is one for which the guideline development group is confident that the desirable effects of adherence outweigh the undesirable effects. Implications of a strong recommendation for patients are that most people in their situation would desire the recommended course of action and only a small proportion would not. Implications for clinicians are that most patients should receive the recommended course of action, and adherence to this recommendation is a reasonable measure of good-quality care. With regard to policy-makers, a strong recommendation means that it can be adapted as a policy in most situations, and for funding agencies it means the intervention probably represents an appropriate allocation of resources (i.e. large net benefits relative to alternative allocation of resources).

# Estimated salt consumption a
, g/day b This fortification concentration was calculated based on the mean recommended nutrient intake of 150 g iodine/day + 30% losses from production to household level before consumption, and a 92% iodine bioavailability. Losses depend on the iodization process, the quality of salt and packaging materials and the climatic conditions. Losses could vary widely (50) and this table presents the value considering 30% losses. The monitoring of urinary iodine concentrations will allow adjustment of the selected fortification concentrations.
RNI: recommended nutrient intake, is the daily intake, set at the estimated average requirement plus 2 standard deviations, which meets the nutrient requirements of almost all apparently healthy individuals in an age-and sex-specific population group.
Although iodate is more stable, either potassium iodate (KIO 3 or iodide (KI) can be used. Iodide may be used for dry, low crystal size and washed or refined salts. While iodate can be used alone and in any type of salt quality, iodide is used in very good quality salt and cannot be added alone. Therefore, some salt producers add sodium carbonate or sodium bicarbonate when they iodize salt, to increase alkalinity, and sodium thiosulfate or dextrose to stabilize potassium iodide. Without a stabilizer, potassium iodide may be oxidized to iodine and lost by volatilization from the product (53).
An estimated additional variability of 10% during iodization procedures could be considered at the production site for use in quality control and assurance procedures. This variability depends on the iodization methods used and quality assurance system in place.
Shaded areas correspond to the WHO salt reduction guideline (33).
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 14 Remarks
These recommendations recognize that salt reduction and salt iodization are compatible. Monitoring of sodium (salt) intake and iodine intake at country level is needed to adjust salt iodization over time as necessary, depending on observed salt intake in the population, to ensure that individuals consume sufficient iodine despite reduction of salt intake (33).
The concentrations of iodine may need to be adjusted by national authorities responsible for the implementation and monitoring of universal salt iodization, in light of their own data regarding dietary salt intake (30).
The national distribution of salt consumption must provide key guidance for the concentration of iodine in salt (29,31); sufficient iodine should be supplied to most members of the population, even those with the lowest salt intake, while at the same time preventing excessive iodine supply to those individuals whose salt intake remains high.
- Iodized salt should reach, and be used by, all members of the population after 1 year of age. Infants and young children are assumed to be covered via breast milk (4) or iodine-enriched infant formula milk when this is prescribed (54). Addition of salt to products consumed by young children may need regulation, to avoid insufficient or excessive consumption of either sodium (salt) or iodine.
- Since pregnant women have a daily iodine requirement of 250 g/day, other interventions such as iodine supplementation could be considered if iodine inadequacy is found (55,56). Intake of salt correlates with caloric intake, and pregnant women usually increase their energy intake during this physiological stage.
- Policies for salt iodization and reduction of salt to <5 g/day are compatible, cost effective and of great public health benefit. Although salt is an appropriate vehicle for iodine fortification, iodization of salt should not justify promotion of salt intake to the public (30).
- Monitoring of food-grade salt quality is essential to ensure both efficacy and safety of the process of iodine fortification. Monitoring of UIE and UIC is useful not only to detect deficiency but also to detect excessive intakes and therefore prevent the health risks of iodine excess, by adjusting the level of iodine fortification accordingly, as part of a monitoring system. Countries should determine iodine losses from iodized salt under local conditions of production, climate, packaging and storage. For these reasons, iodine losses may be extremely variable and influence the additional amount of iodine that should be added at factory level.
- Fortification of salt with iodine should be appropriately regulated by governments and harmonized with other local or country programmes, to ensure that fortified food-grade salt is delivered safely within the acceptable dosage range. Particular attention should be given to identifying potential barriers to equitable access for all population groups needing iodine-fortified salt.
- Country programmes should be culturally appropriate to the target populations, so the intervention is accepted, adopted and sustained.
- Clear legislation should also be established for food producers and distributors, especially where the main source of dietary salt is processed foods and meals consumed outside households. Legislation should cover not only proper iodization of salt, but also the salt content of industrialized food products.
- Establishment of an efficient system for the ongoing and routine collection of relevant data, including measures of quality assurance and household use of iodized salt, and measures of programme performance, is critical to ensure programmes for iodized salt are effective and sustained.
- Regular monitoring and evaluation can identify barriers that may be limiting equal access to fortified salt and thus preserving health inequities. Sustained implementation and scale-up derive great benefit from appropriate monitoring mechanisms (4).

# Implications for future research
Discussions with members of the WHO guideline development group and the external review group highlighted the limited evidence available in some areas, meriting further research on the fortification of food-grade salt with iodine, in particular in the following areas:
- determination of the relationships between iodine excretion (24-h collection) and urinary (UIC in different ages, sexes, and physiological stages (mainly pregnancy and lactation), and under different climatic conditions and levels of physical activity, in order to adjust the criteria for UIC for population assessments;
- determination of the relative contribution to iodine intake from table salt and from processed foods;
- investigation of the usefulness of Tg as a functional indicator of iodine status, to complement the use of UIC as an indicator of iodine intake;
- investigation of whether iodine deficiency (mild or moderate) is occurring in pregnant and lactating women worldwide, and the potential negative impact in their health, as well as on development of their offspring;
- alignment of national salt-iodization and dietary salt-reduction programmes, including optimization of policy implementation and ensuring effective monitoring and coordination of monitoring;
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 16 6. understanding the potential impact of salt-containing processed foods, such as bouillon cubes, condiments and powder soups, and other edible vehicles;
- identification of the optimal indicators to assess iodine nutrition during pregnancy, lactation and infancy. The use of neonatal serum concentration of TSH as an indicator of iodine status in pregnancy needs further validation;
- better prevalence data on the iodine status of pregnant and lactating women, and infants;
- more data from large studies of the impact of iodine-intervention programmes on iodine-induced thyroiditis and iodine-induced hyperthyroidism;
- further studies to correct misperceptions that link iodized salt to certain diseases, as well as the barriers that might be encountered during implementation and scale-up, such as consumer demand for non-iodized salt, religious concerns relating to iodized salt, and the perception of extra costs of purchasing iodized salt. Findings arising from these studies can help identify bottlenecks and barriers to access to iodine-fortified food-grade salt;
- studies to identify the knowledge and awareness of the general population about the use of iodized salt are important to address barriers such as religious concerns and existing demand for non-iodized salt;
- studies to search and evaluate the use of different vehicles for iodine fortification.

# Dissemination, adaptation and implementation
The current guideline will be disseminated through electronic media such as slide presentations and the World Wide Web, through either the WHO Nutrition (57) and United Nations Standing Committee on Nutrition (SCN) (58) mailing lists, social media, the WHO nutrition website (57) or the WHO e-Library of Evidence for Nutrition Actions (eLENA) (59). eLENA compiles and displays WHO guidelines related to nutrition, along with complementary documents such as systematic reviews and other evidence that informed the guidelines; biological and behavioural rationales; and additional resources produced by Member States and global partners. In addition, the guideline will be disseminated through a broad network of international partners, including WHO country and regional offices, ministries of health, WHO collaborating centres, the International Council for the Control of Iodine Deficiency Disorders Global Network, universities, other United Nations agencies and nongovernmental organizations.
Particular attention will be given to improving access to these guidelines for stakeholders that face more, or specific, barriers in access to information, or that play a crucial role in the implementation of the guideline recommendations, for example, policy-makers and decision-makers at subnational level that disseminate the contents of the guideline, especially information on the benefits of consuming fortified foodgrade salt in populations or regions presenting an important risk of iodine deficiency. This is remarkably important in rural communities or highly isolated communities, where seeking health care is less frequent, and obtaining health care is more difficult, because of distance or transport barriers (e.g. women before and during pregnancy; infants and young children).
Accessing hard-to-reach population groups is extremely important during implementation stages, as it contributes to preventing or tackling health inequities. Fortified foods, such as corn-soya blend, biscuits, vegetable oil enriched with vitamin A and iodized salt, are usually provided as part of food rations during emergencies (60). In the United Nations system, the World Food Programme is responsible for mobilizing the iodized salt for selective feeding programmes (61). Moreover, dissemination of the guidelines and information on the benefits of consuming fortified food-grade salt in iodine-deficient contexts helps to empower consumers, and thus contributes to creating consumer demand.

# Adaptation and implementation
As this is a global guideline, it should be adapted to the context of each Member State. Prior to implementation, a public health programme that includes the fortification of food-grade salt with iodine should have well-defined objectives that take into account available resources, existing policies, suitable delivery platforms and suppliers, communication channels, and potential stakeholders. Ideally, all food-grade salt should be fortified at a concentration based on the average salt consumption and in line with the country's policy on the reduction of salt intake.
To ensure that WHO global guidelines and other evidence-informed recommendations for nutrition interventions are better implemented in low-and middle-income countries, the Department of Nutrition for Health and Development works with the WHO Evidence-Informed Policy Network (EVIPNet) programme (62). EVIPNet promotes partnerships at country level between policy-makers, researchers and civil society, to facilitate policy development and implementation through use of the best available evidence.
In some countries, implementation of salt-iodization programmes may not be feasible, and increased iodine intake through iodine fortification of foods other than salt may be necessary, to ensure optimal iodine nutrition in relevant groups.
Although fortification of food-grade salt is a relatively inexpensive intervention that is likely to be well received by the different stakeholders, it is likely to face difficulties in terms of implementation. Initial resistance from some stakeholders, well-established practices, changes in consumption habits, or potential misbeliefs in certain populations are some of the implementation barriers that could arise. Therefore, any adoption and adaptation of these recommendations at country level and within-country level should bear in mind the following series of key aspects that enhance implementation and scale-up.
Particular attention should be given to the acceptability of the recommendation by the different stakeholders, including the salt companies, food inspection officers and final consumers. For instance, a large share of salt consumption in the population is obtained from industrialized processed foods (63); therefore, commitment from the industry is necessary to implement and scale up this intervention. This is also imperative when food-grade salt is imported. For instance, table salt is sometimes labelled as iodine fortified, but in some cases the content does not match the label; hence the work of food inspection officers is needed (64,65). Likewise, although the taste of fortified foodgrade salt is not different from that of non-fortified salt, there may be certain consumers that prefer non-iodized salt for reasons of perceived taste, religious concerns or alleged medical properties (66), or simply for a perceived violation of consumers' right to choose between a fortified and non-fortified product. Other perceptions may sometimes be based on misunderstandings or misinformation. Consumer demand for non-iodized salt can push local stores and food shops to supply such a product; this circumstance must be taken into account when developing programmes or deploying implementation and should be addressed through information and communication efforts targeting specific audiences. Long-standing experiences and best practices in many countries around the world can inform those countries initiating or enhancing their fortification efforts, to ensure adoption of this intervention.
Acceptability and adoption are better achieved if they are accompanied by simple and easy-to-access information that can be understood by different population groups. Dissemination of information must be carried out in a manner that aims to ensure that these recommendations are perceived as appropriate. In this sense, the appropriateness of consuming iodine-fortified food-grade salt must be fully explained to the target population (including final consumers) in a way that is culturally appropriate and understandable, taking into account consumption habits and religious beliefs, for example. Sometimes, evidence-based and proven interventions fail to be adopted by the population because issues of acceptability and appropriateness are not taken into account during implementation.
Better-informed consumers are more likely to become empowered consumers that demand fortified salt for health reasons. Besides dissemination of appropriate and adapted information on the benefits of iodine fortified-salt in areas or populations presenting risk of iodine deficiency, consumers must be informed about the fact that consuming iodine-fortified salt does not imply additional costs to the household economy -a residual but sometimes prevalent misbelief found in research (66)(67)(68).
In many high-income and middle-income countries, there are some social groups and individuals that promote the consumption of so-called "all-natural foods", especially those that have not undergone the addition of any other "element" to the food itself. Qualitative research on perceptions of fortified foods suggests that, for certain groups, fortification may be viewed as a form of artificial processing, which could be perceived as reducing the health benefits of natural foods (69). Public health programmes should be aware of this misinterpretation of fortified foods, in order to better implement scale-up and respond to potential setbacks in terms of acceptability and adoption by consumers in high-and middle-income countries.
Moreover, linking the implementation of these recommendations with other intersectoral interventions will benefit the sustainability and scale-up of iodine fortification of food-grade salt. For instance, given that the most important iodine intake for any individual is the one that occurs before the mother is pregnant and during pregnancy, the empowerment of women in terms of health literacy and self-care for their health will benefit both women themselves and neonates. Information and advice about how women can take better care of their health before and during pregnancy is essential to encourage consumption of iodized salt in a context where the availability of non-iodized salt is a reality. The unequal sexual division of labour worldwide puts women in the position of making decisions about the food intake of the household; therefore, it is important to improve their access to information and health advice. This is particularly important in low-and middle-income settings, where those who are better off are usually more likely to receive early benefit from health innovations that take time to scale up and become widespread. A second example of the importance of intersectoral action is collaboration with the education sector. Often, children who are in school are provided either a snack or lunch at a school cafeteria. Making sure that processed foods and prepared foods served by these canteens include iodized salt in their preparation is a strategy worth exploring.

# Monitoring and evaluation of guideline implementation
A plan for monitoring and evaluation with appropriate indicators is encouraged at all stages. The impact of this guideline can be evaluated within countries (i.e. monitoring and evaluation of the programmes implemented at national or regional scale) and across countries (i.e. adoption and adaptation of the guideline globally). The WHO Department of Nutrition for Health and Development, Evidence and Programme Guidance Unit, jointly with the United States Centers for Disease Control and Prevention (CDC) International Micronutrient Malnutrition Prevention and Control (IMMPaCt) programme, and with input from international partners, has developed a generic logic model for micronutrient interventions in public health (70), to depict the plausible relationships between inputs and expected MDGs by applying the micronutrient programme evaluation theory. Member States can adjust the model and use it in combination with appropriate indicators, for designing, implementing, monitoring and evaluating the successful escalation of nutrition actions in public health programmes. The WHO/CDC eCatalogue of indicators for micronutrient programmes (71) intends to be a dynamic, user-friendly and non-comprehensive web resource for those actively engaged in providing technical assistance in monitoring, evaluation, and surveillance of public health programmes implementing micronutrient interventions. It provides potential indicators with standard definitions that can be selected, downloaded and adapted to a local programme context. An electronic WHO/CDC eCatalogue of indicators for micronutrient programmes is a repository of indicators to monitor and evaluate micronutrient interventions. The eCatalogue initially includes key programme indicators (inputs, activities, outputs and outcomes) related to salt iodization. While it does not provide guidance for designing or implementing a monitoring or evaluation system in public health, some key indicators may include useful references for that purpose. Median UIC has been proposed for monitoring established salt-iodization programmes and adjusting the iodine content of salt, if needed. The use of data on urinary iodine can serve to adjust fortification levels in food-grade salt throughout implementation of the programme. The levels will serve to inform decisions on whether to review salt consumption, salt quality and iodization procedures, and consider increasing iodization concentrations, continue an actual fortification programme as it stands, or consider reducing iodization levels. The median UIC is a rough estimation, and it depends on the hydration status of the person and the climate where he or she lives. When sampling urinary iodine in iodine-sufficient school-age children, the median UIC may be between 100 and 300 ug/L, at or above the recommended value for pregnant women (72). In countries or regions with a notable rate of school-age children not attending school, iodine sampling may be biased; therefore, sampling could be adjusted if considered appropriate and feasible. As of 2013, there were 57 million school-age children not attending school: 29.8 million in sub-Saharan Africa, 12.4 million in South and West Asia, and 14.9 million in the rest of the WHO regions (20). School attendance may also have an impact on food intake (provision of foods at canteens).
Since 1991, WHO has hosted the Vitamin and Mineral Nutrition Information System (VMNIS) Micronutrients Database (73). Part of WHO's mandate is to assess the micronutrient status of populations, monitor and evaluate the impact of strategies for the prevention and control of micronutrient malnutrition, and track related trends over time. The Evidence and Programme Guidance Unit of the Department of Nutrition for Health and Development manages the VMNIS Micronutrient Database through a network of regional and country offices, and in close collaboration with national health authorities. UNICEF's global databases monitor coverage of salt iodization in countries and incorporate statistically sound and nationally representative data from household surveys, including multiple indicator cluster surveys and demographic and health surveys. These databases are updated annually through a process that draws on data maintained by UNICEF's network of field offices. The databases are publicly available at  (74). Another element that enhances implementation and scale-up is making sure that monitoring and data collection are sensitive to health inequities. For instance, monitoring both industry efforts in fortification and consumer behaviour related to consumption of food-grade salt and industrialized processed foods containing non-iodized salt is key to identifying gaps for effective scale-up and sustainability. Identifying the barriers to an effective supply of iodized salt, and the barriers to strengthening consumer demand for iodized salt, prevents widening of unequal distributions of the benefits of health innovations. No actions tackling health inequities can be further sustained without robust, valuable data.

# Guideline development process
This guideline was developed in accordance with the WHO evidence-informed guideline development procedures, as outlined in the WHO handbook for guideline development (76).

# Advisory groups
The Its role was to advise WHO on the choice of important outcomes for decision-making and on interpretation of the evidence. The WHO guideline development group -nutrition actions includes experts from various WHO expert advisory panels (77) and those identified through open calls for specialists, taking into consideration a balanced gender mix, multiple disciplinary areas of expertise, and representation from all WHO regions. Efforts were made to include content experts, methodologists, representatives of potential stakeholders (such as managers and other health professionals involved in the health-care process), and technical staff from WHO and ministries of health from Member States. Representatives of commercial organizations may not be members of a WHO guideline group.
An external review group peer-reviewed the draft guideline. The WHO Nutrition (57) and SCN (58) mailing lists, which together include over 5500 subscribers, and the WHO nutrition website (57) were used to identify members of the external review group. Additionally, six content experts peer-reviewed the draft guideline and provided technical input.
The Appraisal of Guidelines, Research and Evaluation II (AGREE II) Instrument can be used to assess the methodological rigour for developing this global guideline (78).

# Scope of the guideline, evidence appraisal and decision-making
An initial set of questions (and the components of the questions) to be addressed in the guideline was the critical starting point for formulating the recommendation. The questions were drafted by technical staff at the Evidence and Programme Guidance Unit, Department of Nutrition for Health and Development, based on the policy and programme guidance needs of Member States and their partners. The population, intervention, control, outcomes (PICO) format was used (see Annex 6). The questions were discussed and reviewed by the WHO Steering Committee for Nutrition Guidelines Development and the guideline development group -nutrition actions, and were modified as needed.
A meeting of the guideline development group -nutrition actions was held on 14-16 March 2010, in Geneva, Switzerland, to finalize the scope of the questions and rank the outcomes and populations of interest for the recommendation on the fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders. The guideline development group discussed the relevance of the questions and modified them as needed. The group scored the relative importance of each outcome from 1 to 9 (where 7-9 indicated that the outcome was critical for a decision, 4-6 indicated that it was important and 1-3 indicated that it was not important). The final key questions on this intervention, along with the outcomes that were identified as critical for decisionmaking, are listed in PICO format in Annex 6.
A systematic review (50) was used to summarize and appraise the evidence using the Cochrane methodology for randomized controlled trials and observational studies (49). Evidence summaries were prepared according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to assess the overall quality of the evidence (79). GRADE considers: the study design; the limitations of the studies in terms of their conduct and analysis; the consistency of the results across the available studies; the directness (or applicability and external validity) of the evidence with respect to the populations, interventions and settings where the proposed intervention may be used; and the precision of the summary estimate of the effect.
Both the systematic review and the GRADE evidence profiles for each of the critical outcomes were used for drafting this guideline. The draft recommendation was discussed by the WHO Steering Committee for Nutrition Guidelines Development and at a second consultation with the WHO guideline development group -nutrition actions, held on 23-26 June 2014 in Geneva, Switzerland. The procedures for decision-making are established at the beginning of the meetings, including a minimal set of rules for agreement and decisionmaking documentation. The guideline development group members secretly noted the direction and strength of the recommendation, using a form designed for this purpose, which also included a section for documenting their views on (i) the desirable and undesirable effects of the intervention; (ii) the quality of the available evidence; (iii) values and preferences related to the intervention in different settings; and (iv) the cost of options available to health-care workers in different settings (see Annex 2). Each member used one form, if not advised otherwise after managing any potential conflict of interests. Abstentions were not allowed. The process was improved with the availability of a predefined link to an online form prepared using survey software. Subsequent deliberations among the members of the guideline development group were of private character. The WHO Secretariat collected the forms and disclosed a summary of the results to the guideline development group. If there was no unanimous consensus (primary decision rule), more time was given for deliberations and a second round of online voting took place. If no unanimous agreement was reached, a two thirds vote of the guideline development group members present was required for the approval of the proposed recommendation (secondary decision rule). Divergent opinions could be recorded in the guideline. The results from voting forms are kept on file by WHO for up to 5 years. Although there was no unanimous consensus, more than 80% of the guideline development group members decided it was a strong recommendation.
WHO staff present at the meeting, as well as other external technical experts involved in the collection and grading of the evidence, were not allowed to participate in the decision-making process.
Two co-chairs with expertise in managing group processes and interpreting evidence were nominated at the opening of the consultation, and the nomination was approved by the guideline development group. Members of the WHO Secretariat were available at all times to help guide the overall meeting process, but did not vote and did not have veto power.
Six content experts peer-reviewed the draft guideline. Additionally, a public call for comments on the final draft guideline was released in August 2014. All interested stakeholders were included as part of an external review group and were allowed to comment on the draft guideline only after submitting a signed declaration of interests form. Feedback was received from several stakeholders. WHO staff then finalized the guideline and submitted it for clearance by WHO before publication.

# Management of competing interests
According to the rules in the WHO Basic documents (80), all experts participating in WHO meetings must declare any interest relevant to the meeting, prior to their participation. The declarations of interest statements for all guideline development group members were reviewed by the responsible technical officer and the relevant departments, before finalization of the group composition and invitation to attend a guideline development group meeting.
All guideline development group members, and participants of the guideline development meetings, submitted a declaration of interests form, along with their curriculum vitae, before each meeting. Participants of the guideline development group meetings participated in their individual capacity and not as institutional representatives. In addition, they verbally declared potential conflicts of interest at the beginning of each meeting. The procedures for management of competing interests strictly followed the WHO Guidelines for declaration of interests (WHO experts) (81). The management of the perceived or real conflicts of interest declared by the members of the guideline group is summarized below. 1 Dr Luz Maria De-Regil declared that her present employer is an international nongovernmental organization devoted to the improvement of micronutrient status among infants, children and women. These activities are primarily financed by the government of Canada. The Micronutrient Initiative (MI) is a leading organization working exclusively to eliminate vitamin and mineral deficiencies in the world's most vulnerable populations. MI is leading efforts to reach the last 30% of households still not using iodized salt, by working with small, local salt processors to provide simple and easy iodization techniques. It was decided that Dr De-Regil could be a member of the guideline development group and would disclose her interests and the interests of her organization in the relevant guidelines related to micronutrient interventions, specifically salt iodization. It was required that she disclosed her employer partnership on the International Council for the Control of Iodine Deficiency Disorders Global Network. She participated in the deliberations related to recommendations on fortification of food-grade salt but recused herself from voting on this guideline.
Dr Maria Elena del Socorro Jefferds is employed by CDC. She declared CDC's partnership on the International Council for the Control of Iodine Deficiency Disorders Global Network. It was agreed that she could participate fully in the deliberations and decision-making on this guideline.
Dr Lynette Neufeld declared that her current employer has received funding in the past 4 years for research and programming related to salt iodization. At the moment she is not leading any of these initiatives. In a prior position she held with MI, she commissioned research related to iodine. It was decided that Dr Neufeld could be a member of the guideline development group and had to disclose her and her organization's interests in the relevant guidelines related to micronutrient interventions, specifically salt iodization. It was required that she disclosed her employer partnership on the International Council for the Control of Iodine Deficiency Disorders Global Network. She could participate in the deliberations but she recused herself from the decision-making (voting) on recommendations related to salt iodization.
Ms Rusidah Selamat declared herself to be a member of a National Technical Food Fortification Committee in Malaysia. She has also published articles on iodine deficiency status and iodized salt consumption in Malaysia and the need for wider coverage with iodized salt in Malaysia. It was agreed that Ms Selamat could be a member of the guideline development group and that she declared her membership in the above-mentioned national committees at the beginning of the guideline development group meeting.
All other members made a verbal declaration of their interest and it was considered that they were not relevant for this guideline on fortification of food-grade salt with iodine. External experts also declared their interest but did not participate in the deliberations or decision-making process.

# Plans for updating the guideline
This guideline is planned to be reviewed in 2024. The Department of Nutrition for Health and Development at the WHO headquarters in Geneva, Switzerland, along with its internal partners, will be responsible for coordinating the guideline update, following the formal procedures of the WHO handbook for guideline development (76). WHO welcomes suggestions regarding additional questions for evaluation in the guideline when it is due for review.  5,6 The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

# Annex 1 GRADE "Summary of findings" tables

# Iodized salt for goitre
CI: confidence interval; RCT: randomized controlled trial; OR: odds ratio; RR: risk ratio.

# GRADE Working Group grades of evidence
High quality: further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: we are very uncertain about the estimate. 1 Unclear randomization and allocation of concealment.
2 95% CI crosses null.
3 Non-randomized. 4 Though the results of one study suggested an opposite result from the others, there were too few events to generate a meaningful result (5 in intervention and 4 in control). 5 Very large protective effect of iodized salt. 6 Many studies did not provide sufficient detail to assess the risk of bias.
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders 33 The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: confidence interval; RCT: randomized controlled trial; RR: risk ratio.

# GRADE Working Group grades of evidence
High quality: further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: we are very uncertain about the estimate. 1 Many studies did not provide sufficient detail to assess the risk of bias.
2 Quasi-experimental studies.
3 Large protective effect with iodized salt.
WHO I Guideline: Fortification of food-grade salt with iodine for the prevention and control of iodine deficiency disorders
Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: we are very uncertain about the estimate.