**Submission to F.D.A.**

**28 March 2008**

## 

## Salt & Cardiovascular Disease 

# 

# 

# 

# Written on behalf of 

# World Action on Salt and Health

# Feng J He, Naomi M Marrero, Graham A MacGregor

# 

# 

# 

# 

# 

# 

# 

# Correspondence to:

# Graham MacGregor

# Professor of Cardiovascular Medicine

# Blood Pressure Unit

# St. George\'s University of London

# Cranmer Terrace, 

# London, SW17 0RE

# Tel: 44 (0)208 725 2848

# Fax: 44 (0)208 725 2959 

E-mail: gmacgreg@sgul.ac.uk

#  

# Contents

[**Summary 4**](#summary)

[Introduction 5](#introduction)

[Raised BP is the most important cause of death and disability in the
world 5](#__RefHeading___Toc194484144)

[The benefits of reducing blood pressure in the \"normal" range
6](#the-benefits-of-reducing-blood-pressure-in-the-normal-range)

[Underlying Factors that put up blood pressure
8](#__RefHeading___Toc194484146)

[**Evidence that relates salt to blood pressure**
8](#evidence-that-relates-salt-to-blood-pressure)

-   
-   
-   
-   
-   
-   

[Animal Studies 8](#__RefHeading___Toc194484148)[Human Genetic Studies
9](#__RefHeading___Toc194484149)[Epidemiological Studies
10](#__RefHeading___Toc194484150)[Migration Studies
12](#__RefHeading___Toc194484151)[Intervention Studies
12](#__RefHeading___Toc194484152)[Treatment Trials
13](#__RefHeading___Toc194484153)[**Evidence that relates salt to
cardiovascular disease (CVD)**
18](#evidence-that-relates-salt-to-cardiovascular-disease-cvd)

-   
-   
-   
-   
-   

[Reductions in CVD predicted from BP falls with decreases in salt intake
19](#__RefHeading___Toc194484155)[Ecological studies
19](#__RefHeading___Toc194484156)[Population studies
19](#__RefHeading___Toc194484157)[Prospective cohort studies
20](#__RefHeading___Toc194484158)[Outcome trials
22](#__RefHeading___Toc194484159)[**Other Adverse Effects of Salt**
23](#__RefHeading___Toc194484160)

-   
-   
-   
-   
-   
-   
-   

[Direct effect on stroke 23](#direct-effect-on-stroke)[Direct effect on
left ventricular mass 24](#__RefHeading___Toc194484162)[Cancer of the
stomach 24](#__RefHeading___Toc194484163)[Proteinuria/renal disease
25](#__RefHeading___Toc194484164)[Renal stones/osteoporosis
26](#__RefHeading___Toc194484165)[Asthma
27](#__RefHeading___Toc194484166)[Obesity
27](#__RefHeading___Toc194484167)[**Specific groups -- children**
29](#__RefHeading___Toc194484168)

-   
-   

[Infants 29](#__RefHeading___Toc194484169)[Children and adolescents
30](#__RefHeading___Toc194484170)[**Worldwide actions occurring on
salt** 31](#__RefHeading___Toc194484171)

[The United Kingdom 31](#__RefHeading___Toc194484172)

-   
-   
-   
-   

[Reduction in the salt content of processed food
32](#__RefHeading___Toc194484173)[Consumer awareness campaign
33](#__RefHeading___Toc194484174)[Working with third sectors partners
33](#__RefHeading___Toc194484175)[Working with third sectors partners
33](#__RefHeading___Toc194484176)[Finland
33](#__RefHeading___Toc194484177)

[Other countries 34](#__RefHeading___Toc194484178)

[Labelling 36](#section-15)

[Why are some members of the food industry so reluctant to reduce the
salt content of processed foods? 37](#__RefHeading___Toc194484180)

[**Conclusion** 39](#conclusion)

[References 40](#__RefHeading___Toc194484182)

# Summary

Worldwide cardiovascular disease (strokes, heart attacks and heart
failure) is the most important cause of death and disability. In the
USA, it is the leading cause of mortality with approximately 870,000
deaths per year^1^. Raised blood pressure, cholesterol and cigarette
smoking are known to be responsible for more than 80% of all
cardiovascular disease^2^. Of these factors, raised blood pressure is
the most important factor, accounting for 60% of all strokes and 50% of
coronary heart disease^3^. Importantly, the risk of cardiovascular
disease is not confined to those with raised blood pressure, but
throughout the range, starting at a systolic pressure of 115 mmHg^4^.
This means that the majority of adults are at risk from their blood
pressure.

Any intervention that lowers blood pressure will prevent both strokes,
heart attacks and heart failure, even a small reduction of 2 mmHg in
population systolic pressure would carry more benefit than all of the
blood pressure treatment currently being given. In the longer term,
there would be an even greater benefit, particularly if it slowed down
the rate of increase in blood pressure with age, as this would cause
much larger decreases in population blood pressure.

Our current consumption of salt is the major factor putting up blood
pressure. Very strong evidence now indicates that a modest reduction in
salt intake by one third, or ideally to half of the current consumption,
would lead to a reduction in population blood pressure and a reduction
in the rise in blood pressure with age. A 6 gram reduction in salt
intake would cause an approximately 24% reduction in stroke deaths and
20% reduction in heart attack deaths^5^, and in the USA would prevent
about 150,000 cardiovascular deaths each year. Furthermore, reducing
salt intake is by far the most practical and easiest dietary change to
implement as it does not necessarily need a change in the food currently
being consumed, provided less salt is added to it by the food industry.

**[This reduction in salt intake can be achieved by:]{.underline}**

-   **Clear labelling** of the salt content of all foods where salt has
    been added

-   **A gradual reduction** in the salt concentration of all foods where
    salt has been added

-   **A public campaign** about the dangers of eating too much salt and
    the benefits of reducing all forms of salt consumption.

# Introduction

For several million years the ancestors of humans ate a diet that
contained \<0.25 gram of salt per day. Humans are therefore genetically
programmed to this amount of salt. The recent change, in evolutionary
terms, to the high salt intake of 10-12 gram/day^6,\ 7^ presents a major
challenge to the physiological systems to excrete these large amounts of
salt through the kidney. There has been little time for physiological
systems to adapt. The consequence is that the high salt causes a rise in
blood pressure (BP)^6,\ 8,\ 9^, increases the risk of cardiovascular
disease (CVD)^10^, renal disease^11-13^, bone demineralization^14^ and
stomach cancer^15^.

**Raised BP is the most important cause of death and disability in the
world**[]{#__RefHeading___Toc194484144 .anchor}

![](media/image1.wmf){width="5.375in" height="4.114583333333333in"}In
the late nineteenth century, life assurance and mortgage companies were
the first to realise that the higher the BP, the greater the chances of
dying at an earlier age. Extensive epidemiological work and treatment
trials have subsequently confirmed this finding. A recent systematic
analysis of population health data shows that not only is raised BP the
biggest cause of death worldwide, but the second biggest cause of
disability coming after malnutrition in children (Figure 1)^16^.

> **Figure 1.** Deaths and disease burden due to leading global risk
> factors. Redrawn from Ref ^16^.

# 

# 

# The benefits of reducing blood pressure in the \"normal" range

It is well documented that BP is directly related to CVD (i.e. strokes,
heart attacks and heart failure) which is the leading cause of death and
disability in the world^16^. There are three major causes of CVD: raised
BP, raised cholesterol and smoking, and over 80% of CVD is due to these
three factors^2^. However, raised BP is the single most important cause,
responsible for 62% of strokes and 49% of coronary heart disease
(CHD)^3^.

The relationship between BP and CVD displays a continuous graded
relationship beginning at 115/75 mmHg (Figure 2)^4^. This indicates that
for most countries in the world, over 80% of all adults are at risk from
their BP.

Although the risk of CVD increases progressively with increasing BP, for
the population at large, the greatest number of CVD attributable to BP
occur in the upper range of average (i.e. BP around 130/80mmHg) because
there are so many individuals having BP at these levels in the
population^17^ (Figire 3). Therefore, a population-based approach, e.g.
a reduction in salt intake, aimed at achieving a downward shift in the
distribution of BP in the whole population, even by a small amount, will
have a large impact on reducing the appalling burden of CVD. Geoffrey
Rose pointed out many years ago that even a 2 mmHg reduction in systolic
pressure in the whole population would carry more benefit than all of
the blood pressure treatment currently being given. In addition, recent
studies of individuals at high risk of cardiovascular disease have
demonstrated the very large benefits of reducing blood pressure even in
the \"normal\" (average) range^18,\ 19^.

![](media/image2.wmf){width="5.997916666666667in"
height="4.186111111111111in"}

**Figure 2.** Relationship between blood pressure and stroke mortality
by age group in a meta-analysis of individual data for one million
adults in 61 prospective studies. From Ref ^4^

> **[Number of Strokes Attributable to BP in Population]{.underline}**

  -----------------------------------------------------------------------
  ![](media/image3.wmf){width="3.9805555555555556in"
  height="2.842361111111111in"}

  -----------------------------------------------------------------------

**Figure 3.** Absolute number of strokes in 405000 individuals in seven
prospective observational studies by baseline diastolic blood pressure.
(Redrawn from Ref.^17^).

**Underlying Factors that put up blood
pressure**[]{#__RefHeading___Toc194484146 .anchor}

Evidence suggests that obesity coupled with a lack of exercise are
important factors involved in the development of high blood pressure.
However, there is much stronger evidence to suggest that salt intake is
related to the development of hypertension, and in particular the rise
in blood pressure with age^20^, and that potassium intake has the
opposite effect and may, in certain circumstances, partially offset the
effects of a high salt intake^21^. Excess alcohol intake is
epidemiologically related to blood pressure, but the effect appears to
be transient and there is debate as to whether excess alcohol intake
causes a more sustained increase in blood pressure. Other dietary
factors, eg calcium, magnesium and fat and protein intake have also been
studied but so far the results are inconsistent.

#### Evidence that relates salt to blood pressure 

A large number of studies have been conducted, all of which support the
concept that salt intake is the major factor increasing population blood
pressure. The diversity and strength of the evidence is much greater
than for other lifestyle factors, eg overweight, lack of fruit and
vegetable consumption and lack of exercise. The evidence that links salt
to blood pressure is as strong as that linking cigarette smoking to
cancer and heart disease.

+-----------------------------------+-----------------------------------+
| -   Animal Studies                | -   Migration Studies             |
+-----------------------------------+-----------------------------------+
| -   Human Genetic Studies         | -   Intervention Studies          |
+-----------------------------------+-----------------------------------+
| -   Epidemiological Studies       | -   Treatment Studies             |
+-----------------------------------+-----------------------------------+

-   **Animal Studies**[]{#__RefHeading___Toc194484148 .anchor}

Numerous studies in rat, dog, chicken, rabbit, baboon and chimpanzee
have all shown that salt intake plays an important role in regulating
BP. Furthermore, in all forms of experimental hypertension, whatever the
animal model, a high salt intake is essential for blood pressure to
rise. A recent study in chimpanzees (98.8% genetic homology with man)
demonstrates that a gradual increase in salt intake from 0.5 gram/day
which is close to humans' evolutionary intake, to 10-15 gram/day which
is similar to our current salt intake, causes a progressive rise in BP
(Figure 4) ^22^.

> ![](media/image4.wmf){width="5.031944444444444in"
> height="3.4208333333333334in"}
>
> **Figure 4.** Blood pressure in chimpanzees who either continued on
> their usual diet (0.5g salt/day) or on an increased salt intake (10-15
> g salt/day). At the end of the 20-month study, the salt supplements
> were stopped and blood pressure declined to that of the control group.
> (Adapted from Ref. ^22^).

-   **Human Genetic Studies**[]{#__RefHeading___Toc194484149 .anchor}

There are several very rare genetic causes of high blood pressure. All
of these result in a reduction in the kidney\'s ability to excrete salt,
and thereby cause high blood pressure. This is considerably aggravated
if salt is consumed ^23,\ 24^. Rare genetic causes of low blood pressure
have also been described. These result in the kidney being unable to
hold on to salt normally, thereby causing low blood pressure. These
forms of low blood pressure are ameliorated by high salt intake.
Overall, these studies clearly indicate the importance of salt intake in
regulating blood pressure in humans.

-   **Epidemiological Studies**[]{#__RefHeading___Toc194484150 .anchor}

There are now over 40 reports and studies in undeveloped societies who
do not or did not have access to salt. These societies have lower blood
pressure compared to developed societies and no rise in blood pressure
with age. Whilst there may be other factors that also account for the
lower blood pressure, several studies have clearly demonstrated the
profound importance of salt intake alone. For instance, a study in the
Pacific Islands where one undeveloped community used seawater in their
food and the other did not, showed the community using seawater had
higher blood pressure^25^. Another study in Nigeria of two rural
communities, one of which had access to salt from a salt lake and the
other did not, showed differences in salt intake and differences in
blood pressure, and yet in all other aspects of lifestyle and diet the
two communities were similar. The Qash\'qai, an undeveloped tribe living
in Iran who have access to salt deposits on the ground, develop high
blood pressure and a rise in blood pressure with age similar to that
which occurs in western communities, but in all aspects live a lifestyle
similar to undeveloped communities who do not have access to salt^26^.

In spite of this evidence, it was felt necessary to set up a carefully
controlled study of 52 communities throughout the world -- the InterSalt
Study^27^ - with individual measurements of blood pressure, weight and
24 hour urinary sodium and potassium. The intention was to study
communities with a wide range of salt intake, ie from 0.5 grams per day
to 25 grams per day.

However, only four communities studied had a low salt intake (ie 3 grams
per day or less) and the rest lay between 6 and 12 grams of salt per day
and none had the high salt intake as originally envisaged. Nevertheless,
the study showed there was a significant positive relationship between
salt intake (as judged by 24 hour urinary sodium excretion) and blood
pressure. There was also a highly significant positive relationship
between salt intake and the increase in blood pressure with age (Figure
5). This relationship showed that an increase in 6 grams of salt per day
over 30 years would lead to an increase in systolic pressure in the
whole population by 9 mmHg^27^.

![](media/image5.wmf){width="6.381944444444445in"
height="4.445833333333334in"}

**Figure 5.** The relation of salt excretion to the slope of the rise in
systolic blood pressure with age in 52 centres in the INTERSALT study.
(Adapted from Ref.^27^).

One criticism of the InterSalt study made by the Salt Institute (a
public relations company defending the interests of salt extractors and
manufacturers worldwide) was that when the four communities consuming
less salt were excluded, there was no overall relationship remaining
between salt intake and blood pressure in these 48 communities.
Subsequently, the Salt Institute published a paper criticising the
statistics of the study. The InterSalt Study\'s authors re-analysed
their data and the results were published simultaneously^28^. The
conclusion was that the re-analysis strengthened the original InterSalt
results and their conclusions still stood that salt intake was related
to blood pressure throughout different populations in the world, and
that there was a robust relationship between salt intake and the rise in
blood pressure with increasing age.

The recently published INTERMAP study (International study of macro- and
micro-nutrients and BP)^29^, and the analysis of EPIC-Norfolk study (the
Norfolk Cohort of the European Prospective Investigation into
Cancer)^30^ have lent further support for the important role of salt in
determining the levels of BP in the population.

-   **Migration Studies**[]{#__RefHeading___Toc194484151 .anchor}

A number of studies have shown that migration from isolated low-salt
societies to an urban environment with a high salt intake is associated
with an increase in BP^31,\ 32^. For example, a well controlled
migration study of a rural tribe in Kenya showed that on migration to an
urban environment, there was an increase in salt intake and a reduction
in potassium intake and blood pressure rose compared to those in a
similar control group who remained in the rural environment^32^. The
increase in salt intake was an important factor in the increase in blood
pressure and furthermore, the stress of the urban environment may have
caused additional retention of sodium above that which would have
occurred with the increase in salt intake.

-   **Intervention Studies**[]{#__RefHeading___Toc194484152 .anchor}

Several population-based intervention studies have been carried
out^33-36^. Some of the studies failed to achieve a reduction in salt
intake, it is therefore not surprising that there was no difference in
BP in such studies^35,\ 36^. However, the studies where salt intake was
successfully decreased demonstrate a reduction in population BP. The
most successful intervention study is the one conducted in two similar
villages in Portugal^33^ which achieved a difference of ≈50% in salt
intake between the two villages by vigorous health education to reduce
salt especially from those foods that had previously been identified as
the major sources of salt in the intervention village. After 2 years'
intervention, there was a difference of 13/6 mmHg in BP between the two
villages (Figure 6).

> ![](media/image6.wmf){width="5.995138888888889in"
> height="4.395138888888889in"}
>
> **Figure 6.** Blood pressure changes with time in two Portuguese
> villages, one of which was advised on how to reduce salt intake and
> given processed foods with a reduced salt content, the other had
> similar measurements of blood pressure but no advice on diet. Note the
> significant differences in blood pressure at 1 year and continuing
> differences at 2 years. (Adapted from Ref.^33^).

A recent randomised community-based intervention trial was carried out
in 550 individuals in two rural villages in north-eastern Japan. The
study demonstrated that dietary counselling for one year reduced salt
intake by 2.3 gram/day as measured by 24-hour urinary sodium and this
was associated with a decrease of 3.1 mmHg in systolic BP^37^.

-   **Treatment Trials**[]{#__RefHeading___Toc194484153 .anchor}

Studies, since the early 1900s, have shown that in those subjects with
high blood pressure, restricting salt intake causes large falls in blood
pressure. The classic studies of Kempner clearly showed major effects,
even in very severe hypertension^38^.

More recently, more modest reductions in salt intake, i.e. from an
intake of 10 to 12 grams per day to around 5 to 6 grams per day, have
been shown to cause falls in blood pressure in hypertensives equivalent
to single drug therapy^39^. These falls are larger in those subjects
with lower levels of plasma renin activity or angiotensin II, for
example those of African origin^40,\ 41^ or older subjects. Furthermore,
modest reductions in salt intake have been shown to be additive to drug
treatment^42^.

A double blind study of salt reduction with three salt intakes - 12, 6
and 3 grams per day in subjects with mild untreated essential
hypertension showed a clear dose response to the salt reduction with
large falls in blood pressure on 3 grams of salt per day^43^.
Furthermore blood pressure remained controlled on the lower salt intake
at one year of follow up.

Three longer term studies from the USA have also demonstrated that quite
small reductions in salt intake not only lower blood pressure, but may
also prevent the development of hypertension, and may allow the
withdrawal of drug therapy^44^.

A double-blind study in older subjects demonstrated that the fall in
blood pressure in normotensive individuals with a modest reduction in
salt intake from 10 to 5 grams of salt per day, was the same as those
with high blood pressure^45^. This suggested a large potential benefit
of salt reduction in preventing strokes in this vulnerable elderly group
who have blood pressure in the upper range of normal.

More recently, the DASH Sodium Study, a well controlled feeding study,
has clearly demonstrated that reducing salt intake lowers blood pressure
substantially, not only in hypertensives but also in normotensives, and
importantly there was a dose-related response^41^. Furthermore, there
was a further fall in blood pressure with the salt restriction when a
separate group of patients were fed a DASH diet consisting of more fruit
and vegetables and less saturated fat. This study is of importance in
that it demonstrates that not only would there be benefit from reducing
salt intake on the diet that we currently consume, but there would be
additional effects of restricting salt intake and consuming more fruit
and vegetables and reducing saturated fat intake (Table 1, Figure 7).

**Table 1**. Fall in blood pressure with salt restriction alone or the
combination of salt restriction and DASH-diet in hypertensive and
normotensive individuals in the DASH-Sodium study.

  ----------------------------- ----------------- -----------------------
                                **Hypertensives   **Normotensives
                                (n=169)**         (n=243)**

  **Salt restriction alone**    **8.3/4.4 mmHg**  **5.6/2.8 mmHg**

  **Salt restriction + DASH     **11.5/5.7 mmHg** **7.1/3.7 mmHg**
  diet**                                          
  ----------------------------- ----------------- -----------------------

> ![](media/image7.wmf){width="4.738194444444445in"
> height="7.751388888888889in"}
>
> **Figure 7.** Changes in blood pressure and 24 h urinary sodium
> excretion with the reduction in salt intake in all participants
> (hypertensives: n=169; normotensives: n=243) on the normal American
> diet (i.e. control diet) and on DASH diet. (Redrawn from Ref.^41^).

In spite of the clear results of the DASH Sodium study and the very
carefully controlled double blind studies, some controversy has
surrounded the effect of modest salt reduction in those with \"normal or
average\" blood pressure. Meta-analyses of a variety of studies that
have been undertaken in normotensives have shown small, but consistent,
reductions in systolic pressure^46^. Two meta-analyses of the effect of
salt restriction on blood pressure showed that whilst the fall in blood
pressure was significant in normotensive subjects, it was, according to
the authors, of insufficient degree to be of public health
importance^47,\ 48^. Close examination of these two meta-analyses shows
that they are seriously flawed as they included many studies where salt
intake had only been reduced for five days and there were very large
reductions in salt intake, e.g. from 20 grams per day to less than 0.5
grams of salt per day over five days. This is known to cause stimulation
of the sympathetic nervous system and brisk activation of the
renin-angiotensin system^49^. These very short acute reductions in salt
intake are not relevant to the public health recommendations of a more
modest reduction in salt intake from 10-12 grams per day to 5-6 grams
per day, and in no way would the blood pressure lowering effect of a
drug be judged over only five days of treatment.

A more recent meta-analysis looked only at studies of one month or more
in duration and only included studies with modest reductions in salt
intake similar to the public health recommendations. This meta-analysis
demonstrated a significant fall in blood pressure, both in systolic and
diastolic blood pressure, not only in hypertensives but also in
normotensive individuals^46^ (Figure 8). The meta-analysis also showed a
dose response relationship, so that a 6 gram reduction in salt intake
would result in a fall in systolic blood pressure in the normotensive
subjects of 4.0 mmHg^5^ (Figure 9).

Most studies in the meta-analysis mentioned have been for one month only
and it is likely that a longer duration of salt reduction would have a
greater effect, particularly if it also prevented or slowed down the
rise in blood pressure with age. The meta-analysis is also likely to
under-estimate the fall in blood pressure, as illustrated by the much
larger falls in blood pressure that were seen in the very well
controlled DASH Sodium study^41^ and the other double blind studies of
salt reduction^43^.

> ![](media/image8.wmf){width="5.139583333333333in"
> height="7.419444444444444in"}
>
> **Figure 8**. Effect of modest salt reduction on blood pressure in
> hypertensive and normotensive individuals in a meta-analysis of 28
> randomised controlled trials of 4 or more weeks. (Note average salt
> intake was reduced from 10 to 5 grams/day). (Adapted from Ref.^46^).

![](media/image9.wmf){width="4.548611111111111in" height="4.075in"}

> **A 6 g/day reduction in salt intake predicts a fall in SBP of:**
>
> **7 mmHg in Hypertensives (p\<0.001)**
>
> **4 mmHg in Normotensives (p\<0.01)**
>
> **Figure 9**. Dose-response relationship between the reduction in salt
> intake as judged by reduction in 24h urinary sodium and systolic blood
> pressure. (Adapted from Ref ^5^).

#### 

#### Evidence that relates salt to cardiovascular disease (CVD)

One of the difficulties in drawing conclusions about the importance of
salt in the prevention of CVD is the limited evidence on CVD outcome
from randomised trials. One has to accept that outcome trials of
reducing salt or changing other dietary and lifestyle factors, in the
population are extremely difficult. However, several lines of evidence
have consistently shown that a higher salt intake is related to a higher
risk of CVD.

**[Reductions in CVD predicted from BP falls with decreases in salt
intake]{.underline}**[]{#__RefHeading___Toc194484155 .anchor}

As raised BP throughout the range is the major cause of CVD, a reduction
in salt intake lowers BP and would be predicted to reduce CVD. Based on
the falls in BP from a meta-analysis of randomised salt reduction
trials^46^, we estimated that a reduction of 6 gram/day in salt intake
would reduce strokes by 24% and CHD by 18%. This would prevent ≈35,000
stroke and coronary deaths a year in the UK^5^ and ≈2.5 million
worldwide.

Apart from its BP-lowering effect, a reduction in salt intake may have
other beneficial effects on the cardiovascular system^50^ which may be
independent of and additive to its effect on BP, e.g. a direct effect on
stroke^51^, left ventricular hypertrophy^52^, renal disease and
proteinuria^11-13^. Therefore, the total effect of salt reduction on
cardiovascular outcomes may be larger than those estimated from BP falls
alone.

**[Ecological studies]{.underline}**[]{#__RefHeading___Toc194484156
.anchor}

Ecological analyses have shown a significant relationship between salt
intake and stroke mortality^51,\ 53^. It was also found that the
association of 24-hour urinary sodium with stroke mortality was stronger
than that with BP.

**[Population studies]{.underline}**[]{#__RefHeading___Toc194484157
.anchor}

In the late 1950s the Japanese became aware that certain parts of Japan,
particularly the north, had a high salt consumption and deaths from
stroke were amongst the highest in the world. It was then found that the
numbers of strokes in different parts of Japan were directly related to
the salt intake. In view of these findings, there was a Government
campaign to reduce salt intake, which was successful in reducing salt
intake over the following decade from an average of 13.5 grams per day
to 12.1 grams per day. However, in the north of Japan the salt intake
fell from 18 grams per day to 14 grams per day. At the same time, there
was a fall in blood pressure both in adults and children, and an 80%
reduction in stroke mortality^54^,^55^. At the time of this fall and the
reduction in stroke mortality, there were large population increases in
fat intake, cigarette smoking, alcohol consumption and an increase in
weight. It would appear that the Western influence which was rapidly
overtaking Japan seemed to have little effect on blood pressure,
provided salt intake was reduced, and overall the reduction in salt
intake appeared to be associated with large falls in deaths from stroke.

Since the early 1970s, Finland has had a policy of reducing salt intake
in the whole population^56,\ 57^. The strategy has been a
community-based collaboration with the food industry to develop
reduced-salt food products and raise the general awareness of the
harmful effects of salt on health. During the past 30 years, salt intake
was reduced by one-third. This was accompanied by a fall of over 10 mmHg
in both systolic and diastolic BP, a pronounced decrease of 75-80% in
both stroke and CHD mortality, and a remarkable increase of 5 to 6 years
in life expectancy^56^. The reduction in salt intake is a major
contributory factor for these results, particularly the fall in BP as
both body mass index and alcohol consumption have increased during that
period. An increase in potassium intake via the use of reduced-sodium,
potassium- and magnesium-enriched salt and an increased consumption of
fruit and vegetables, and a reduction in fat intake also play a part in
the fall in CVD.

**[Prospective cohort
studies]{.underline}**[]{#__RefHeading___Toc194484158 .anchor}

A total of 9 prospective cohort studies have looked at the relationship
between salt intake and cardiovascular outcomes. These include the
Honolulu Heart Study^58^, the NY Worksite Study^59^, the Multiple Risk
Factor Intervention Trial (MRFIT)^60^, the Scottish Heart Health
Study^61^, the National Health and Nutrition Examination Survey
(NHANES)-I ^62,\ 63^, the Health Professional Study^64^, the Finnish
cohort^65^, the Japanese cohort^66^, and NHANES II^67^. Among these 9
studies, 7 used dietary method (i.e. 24-hour dietary recall or food
frequency questionnaire) to assess salt intake. It has been shown that
these dietary methods are unreliable in estimating the amount of salt
people eat, particularly as no account is taken of discretionary salt
which in the 1970's would have contributed substantially to salt intake
and most of these studies had baseline salt intake measured around that
time. The dietary methods have been severely criticised previously. For
instance, Karppanen and Mervalaala marvelled that many women in the
group with the lowest salt intake who had a calorie intake near
starvation level, had survived for 20 years in NHANES-I follow-up
study^68^. Due to the methodological flaws, the results from these
studies should be interpreted with great caution.

Twenty-four-hour urinary sodium is the only accurate way to measure salt
intake. Among the 9 prospective studies, 3 had 24-hour urinary sodium
measured. However, in one study (i.e. the NY Worksite Study)^59^,
24-hour urinary sodium was measured after all hypertensive individuals
had their salt intake restricted for five days and no measurement was
made on the subjects\' normal diet. Furthermore, analysis of 24-hour
urinary data revealed severe methodological problems as individuals in
the lowest quartile of salt intake had a much lower 24-hour urinary
creatinine indicating incomplete collection of 24-hour urine. The
results from this study therefore cannot be used to look at the effects
of salt restriction.

The Scottish Heart Health Study^61^ which enrolled a random sample of
11629 individuals aged 40-59 years, had 24-hour urinary sodium measured
while on individuals' usual diet. The follow-up data showed that a
higher salt intake was significantly associated with a higher risk of
all coronary events in women, but the association was not significant in
men. Another prospective cohort study was carried out in a random sample
of 2436 Finnish men and women aged 25--64 years^65^. All participants
had 24-hour urinary sodium measured while on their usual diet. This
study showed that a higher salt intake was significantly associated with
a higher risk of death from CHD and CVD. An increase of 6 gram/day in
salt intake was related to an increase of 56% in CHD deaths, 36% in CVD
deaths and 22% in all deaths (Figure 10). This study also showed that a
higher salt intake increased the risk of CVD in both normal weight and
overweight people, and the effect is larger in those who are overweight.

![](media/image10.wmf){width="5.379166666666666in" height="3.88125in"}

> **Figure 10.** The hazards ratios for coronary heart disease (CHD),
> cardiovascular disease (CVD), and all-cause mortality associated with
> a 6 g/day increase in salt intake as judged by 24 hour urinary sodium
> excretion. (Adapted from Ref.^65^)

**[Outcome trials]{.underline}**[]{#__RefHeading___Toc194484159 .anchor}

In a recently published paper, Cook et al reported the long-term effects
of salt reduction on cardiovascular disease in individuals participating
in two large randomised trials, the Trial of Hypertension Prevention
(TOHP) I and II.^69^ Over 3000 participants without hypertension were
randomised to a reduced salt group for 18 months (TOHP I) or 36-48
months (TOHP II), or to a control group. Salt intake was reduced by 2.6
and 2.0 gram/day in the original TOHP-I and TOHP-II respectively, and
participants were not given further advice after the trials completed. A
follow-up study at 10-15 years post trial showed that individuals who
were originally allocated to the reduced-salt group had a 25% lower
incidence of cardiovascular events after adjusting for confounding
factors (Figure 11).^69^

> ![](media/image11.wmf){width="5.992361111111111in"
> height="4.665972222222222in"}
>
> **Figure 11.** Cumulative incidence of cardiovascular disease (CVD) by
> salt intervention group in the Trial of Hypertension Prevention (TOHP)
> I and II, adjusted for age, sex, and clinic (Adapted from Ref.^69^)

**Other Adverse Effects of Salt**[]{#__RefHeading___Toc194484160
.anchor}

Much of the focus on salt has been on blood pressure. There is now
increasing evidence that salt has other deleterious effects on health,
independent and sometimes additive to that of blood pressure.

-   **Sodium and water retention**

When humans go from a low to a high salt intake, there is retention of
sodium and thereby water and this expands the extracellular volume. This
increase in extracellular volume is a trigger for various compensatory
mechanisms to allow an increase in urinary sodium excretion but at the
expense of continued retention of sodium and water. Approximately 1.5
litres of extracellular fluid is retained and this continues as long as
a higher salt intake is consumed. This increase in extracellular fluid
exacerbates all forms of sodium and water retention, eg heart failure
and is a major cause of oedema (swelling) in women, aggravating both
cyclical and idiopathic oedema^70^.

# Direct effect on stroke

Animal studies and human epidemiological evidence suggests that a high
salt intake has a direct effect on strokes, independent of and additive
to salt\'s effect on blood pressure^51,\ 66^ (Figure 12).

> ![](media/image12.wmf){width="5.540277777777778in"
> height="3.8916666666666666in"}**Figure 12.** Relationship between salt
> intake as judged by 24h urinary salt excretion and stroke mortality in
> Western Europe (Adapted from Ref^51^)

-   **Direct effect on left ventricular mass**

[]{#__RefHeading___Toc194484162 .anchor}

![](media/image13.wmf){width="5.157638888888889in"
height="3.776388888888889in"}Salt intake relates directly and
independently to enlargement of the heart (Figure 13) and reducing salt
intake reduces left ventricular hypertrophy^71^. Left ventricular
hypertrophy is a major risk factor for cardiovascular disease.

> **Figure 13.** Relationship between salt intake and left ventricular
> mass in individuals with systolic blood pressure \>121 mmHg. Adapted
> from Ref^71^.

-   **Cancer of the stomach**

[]{#__RefHeading___Toc194484163 .anchor}

Salt intake is closely related to cancer of the stomach^72^ (Figure 14)
and is likely to be an important pre-disposing cause. Salt in the
concentration found in many processed or instant foods, eg instant
soups, soya sauce, salted cabbage is a profound gastric irritant and may
pre-dispose the individual to H-pylori infection^73^.

> ![](media/image14.wmf){width="5.999305555555556in"
> height="4.811111111111111in"}
>
> **Figure 14.** Relationship between salt intake as judged by 24h
> urinary salt excretion and stomach cancer mortality in 24 countries.
> (Adapted from Ref.^72^)

-   **Proteinuria/renal disease**[]{#__RefHeading___Toc194484164
    .anchor}

In animal studies, increasing salt intake increases protein excretion in
the urine and markedly increases the rate of deterioration of renal
function in experimental forms of renal disease. Studies where salt
intake has been reduced in animals with experimental renal disease show
a slowing of the rate of progression of the renal disease. Studies in
humans have now shown that salt intake relates on a population basis to
the amount of protein or albumin excretion^74,\ 75^ and this is a major
risk factor for developing kidney disease and cardiovascular disease.
Reducing salt intake in a double blind study has now been shown to
reduce proteinuria^76^ (Figure 15). This is even more marked when
combined with an ACE inhibitor^12^. Therefore, individuals who develop
kidney disease should restrict their salt intake because in nearly all
forms of kidney disease the kidney retains sodium and water in the body.
The increase in sodium retention causes an increase in blood pressure
and makes the proteinuria worse and causes a further deterioration in
renal function. Reducing salt intake will lower blood pressure and
almost certainly reduce the rate of deterioration in renal function.
Patients who are on dialysis need to restrict their salt intake as this
reduces the amount of fluid that they drink between dialyses. This
particularly applies to haemodialysis patients, where blood pressure is
a major problem and studies have clearly shown that if they restrict
salt intake there is less gain in weight between dialyses, less
fluctuation in blood pressure and blood pressure is easier to control.

![](media/image15.wmf){width="4.695833333333334in"
height="4.031944444444444in"}

> **Figure 15.** Change in urinary sodium and protein excretion with a
> modest reduction in salt intake in 40 hypertensive blacks. From Ref
> ^76^ .

-   **Renal stones/osteoporosis**[]{#__RefHeading___Toc194484165
    .anchor}

A high salt intake is a major cause of renal stones in humans. This is
due to the effect salt has on urinary calcium excretion. The higher the
urinary sodium excretion, the higher the urinary calcium excretion.
Until recently, it was assumed that when salt intake was increased, the
increase in calcium excretion was compensated for by an exact increase
in intestinal calcium absorption. There is now evidence to suggest that
this is incorrect and that there is a negative calcium balance with
stimulation of mechanisms not only to increase intestinal absorption of
calcium, but to mobilise calcium from bone. A study in post-menopausal
women showed that the loss of hip bone density over two years was
related to the 24 hour urinary sodium excretion at entry to the study
and was as strong as that relating to calcium intake at entry to the
study^77^. Diuretics, through a reduction in extracellular volume,
reduce calcium excretion leading to a positive calcium balance, increase
bone density and reduce bone fractures. Salt reduction is likely to do
the same but there are as yet no trials of salt reduction looking at a
reduction in fractures.

-   **Asthma**[]{#__RefHeading___Toc194484166 .anchor}

Although it is not thought that a high salt intake is a cause of asthma,
epidemiological evidence suggests that the severity of asthma may relate
to salt intake in different countries^78^. This is supported by trial
data, for example, a double-blind study of modest salt restriction
caused a reduction in the severity of asthma attacks and a reduction in
the use of medication and an improvement in the measurement of airways
resistance^79^. The changes seen were only significant in males. A more
recent double-blind study illustrates the mechanism whereby a higher
salt intake exacerbates asthma^80^.

A recent review of both epidemiological and clinical evidence has
concluded that the adoption of a low salt diet for a period of 2--5
weeks may improve lung function and decrease bronchial reactivity in
adults with asthma, whilst salt loading appears to have a detrimental
effect. Similarly, a low salt diet followed for 1 to 2 weeks also
decreased symptoms in people who have exercise-induced asthma^81^. The
authors of the review state \"Collectively, the studies to date
investigating the potential relationship between dietary sodium \[salt\]
and the severity of asthma or airway hyper-responsiveness have provided
support for the hypothesis that increased dietary intake of sodium may
increase the severity of disease in those with asthma.\"

-   **Obesity**[]{#__RefHeading___Toc194484167 .anchor}

A high salt intake has also been suggested as an indirect cause of
obesity, through the effect it has on fluid intake. Research has shown
that, in adults, the current high salt diet of around 10 g/day causes an
increase fluid consumption of 350 mls per day than if the recommended
lower salt diet of 5 g/day was consumed^82^. It is known that a large
proportion of fluid intake comes in the form of soft drinks (it is a
known fact that 25% of fluid intake in the UK is made up of soft
drinks), and it is well documented that an increase intake of soft
drinks is associated with an increased body mass index (BMI).

A study published in 2006 provided further evidence to support the link
between salt and obesity^56^. The authors of the study note that until
1983 salt intake showed a decreasing trend in the United States. The
prevalence of obesity was relatively low at this time and had remained
essentially unchanged from early 1960s to early 1980s. Sales of salt in
the USA were reported to have increased more than 50% from the mid-1980s
to the late 1990s. Between 1977 and 2001, energy intake from sweetened
beverages increased on average by 135% in the United States. During the
same period, the energy intake from milk declined by 38%. The overall
effect on energy intake was a 278 kcal increase per person a day, with
no compensating increase in energy expenditure. During 1999 to 2002, the
prevalence of obesity was 120% higher among men and 99% higher among
women as compared with the 1976 to 1980 figures. The authors state that
the progressive increase in the average intake of salt explains the
parallel increase in the intake of beverages which, in turn, has
contributed to a marked increase in the intake of calories during the
same period in the USA.

A recent analysis of the dataset of the National Diet and Nutrition
Survey for young people in Great Britain showed that, in children aged 4
to 18 years, there was a significant association between salt intake and
total fluid, as well as sugar-sweetened soft drink consumption after
adjusting for potential confounding factors. A difference of 1 g/day in
salt intake was associated with a difference of 100 and 27 g/day
(P\<0.001) in total fluid and sugar-sweetened soft drink consumption
respectively. These results, in conjunction with other evidence,
particularly that from experimental studies where only salt intake was
changed^82^, demonstrate that salt is an important determinant of fluid
and sugar-sweetened soft drink consumption during childhood. If salt
intake in children in the UK was reduced by half (mean decrease: 3
g/day), there would be an average reduction of 2.3 sugar-sweetened soft
drinks per week per child. Sugar-sweetened soft drink consumption has
been shown to be related to childhood obesity by epidemiological studies
^83^ and randomised trials have demonstrated that a reduction in soft
drink consumption leads to a decrease in obesity^84^. A reduction in
salt intake could therefore play a role in helping to reduce childhood
obesity through its effect on sugar-sweetened soft drink consumption.
This would have a beneficial effect on preventing cardiovascular disease
independent of and additive to the effect of salt reduction on blood
pressure.

**Specific groups -- children**[]{#__RefHeading___Toc194484168 .anchor}

**Infants**[]{#__RefHeading___Toc194484169 .anchor}

A well controlled double-blind study in just under 500 new born babies
showed that when salt intake was reduced by about 30% in the reduced
salt group, as judged by spot urinary sodium concentrations, there was a
progressive difference in systolic blood pressure between babies in the
reduced salt and those in the normal salt group ^85^. At the end of six
months the babies on the lower salt intake had a 2.1 mmHg lower systolic
blood pressure (P\<0.01). The study was discontinued at six months.

Many of these babies were restudied 15 years later^86^. There remained a
significant difference in blood pressure, when adjusted, between those
babies who in the first six months of life had had a reduced salt intake
compared to those that had not, suggesting that there was a programming
effect of salt intake in early life, which fits with several studies in
animals (Figure 16).

![](media/image16.wmf){width="5.1375in" height="4.377777777777778in"}

> **Figure 16.** Difference in systolic blood pressure in newborn
> babies, randomised to either a normal salt intake or a moderate
> reduction in salt intake over the first six months of life. At six
> months, the study was discontinued, with all participants resuming a
> normal salt intake. Fifteen years later, a subgroup of those in the
> study had blood pressure re-measured. (Adapted from Ref.^85,\ 86^)

**Children and adolescents**[]{#__RefHeading___Toc194484170 .anchor}

There have been over 20 observational epidemiological studies on salt
and BP in children and adolescents ^87^. Many of these studies did not
show a significant association. This is not surprising given the large
day-to-day intra-individual variations of salt intake. In addition, many
studies had methodological problems, e.g. the methods used to assess
salt intake were unreliable. Among the observational studies that were
methodologically stronger (e.g. multiple measurements of salt intake
were made, urinary sodium was measured, and confounding factors were
controlled for), the majority showed a significant positive association
between salt intake and BP.^87^ For instance, in a carefully conducted
study where 7 consecutive 24-hour urines were collected by all
participants, Cooper et al demonstrated a significant linear
relationship between urinary sodium and systolic BP in 73 children aged
11-14 years, i.e. the higher the salt intake, the higher the systolic BP
^88^. The relationship remained significant after controlling for age,
sex, race, pulse rate, height, and body weight.

A recent meta-analysis of 10 salt reduction trials with 966
participants, demonstrated that a modest reduction in salt intake has a
significant effect on blood pressure in children and adolescents ^89^.
With a 42% reduction in salt intake for an average duration of 2 weeks,
systolic blood pressure was reduced by 1.2 mmHg (P\<0.001) and diastolic
by 1.3 mmHg (P\<0.001). These findings are important in view of the fact
that blood pressure tracks in children, i.e. the higher the blood
pressure during childhood, the higher the blood pressure in adulthood
^90^. A low salt diet, if continued, may well lessen the subsequent rise
in blood pressure with age, which would have major public health
implications in terms of preventing the development of hypertension and
cardiovascular disease later in life ^89^.

Salt intake, due to the increased consumption of processed foods, is
very high in children. Even in 1984, a study in the UK where 24 hour
urines were collected in four to five year old primary school children
showed that the average sodium excretion was 4 to 5 grams of salt per
day ^91^. If this is expressed for adults on a weight/height basis it is
equivalent to 15 to 20 grams per day. This was at a time when
consumption of processed foods by young children was not high. Since
then, children are eating more processed, ready prepared and takeaway
foods - most of which are very high in salt, saturated fat and sugar. It
is now likely that salt intake in children from the age of three to four
onwards is the same as in adults.

**Worldwide actions occurring on salt**[]{#__RefHeading___Toc194484171
.anchor}

Since the 1980s in the U.S., it has been advised that salt intake should
be reduced to 6 g/day. However, these recommendations alone without any
supporting salt reduction activities have had no impact at all on the
amount of salt consumed. This has been demonstrated by the fact that the
per capita use of salt actually increased by approximately 55% from the
mid 1980s to the late 1990s^56^. To achieve the recommended levels of
salt intake for adults and children, a substantial reduction in the
current average salt intake of the population is required. This would be
best achieved using a population-based approach. There are a number of
countries, mainly developed countries that have recognised this and have
implemented a specific salt reduction strategy to lower the salt intake
of the population, which will be discussed in more detail below.

**The United Kingdom**[]{#__RefHeading___Toc194484172 .anchor}

The United Kingdom (UK) is one of the countries leading the way and
setting the example for other countries in salt reduction strategies. In
1994 in the UK, after a careful assessment of all the evidence by an
independent advisory panel appointed by the Government, they recommended
that the population salt intake should be reduced to 6 grams per day or
less. In 2003, a specialist advisory committee to the Food Standards
Agency (FSA) on nutrition reconsidered all of the evidence, and
concluded that salt intake in the UK should be reduced to less than 6
grams/day in all adults and for the first time set targets for
children^92^ (Table 2). These guidelines recognise that the current
targets for both adults and children are not ideal but are practical and
can be achieved, and that once achieved consideration should be given to
reducing salt intake further.

**[Table 2. SACN recommendations for children]{.underline}**

  ----------------------------------- -----------------------------------
  **Age**                             **Target Average Salt Intake
                                      (g/day)**

  0-6 months                          \<1g/d

  7-12 months                         1 g/d

  1-3 years                           2 g/d

  4- 6 years                          3 g/d

  7-10 years                          5 g/d

  11-14 years                         6 g/d

  Adults                              6 g/d
  ----------------------------------- -----------------------------------

As a result of these recommendations the FSA has embarked on a very
important salt reduction programme aiming to reduce salt intake in the
entire UK adult population from 9.5g per day to 6g or less by 2010. This
strategy has a multi-faceted approach:

1.  **Reduction in the salt content of processed
    food**[]{#__RefHeading___Toc194484173 .anchor}

The FSA is working with the food industry to lower the salt content of
processed food. As a guide to the food industry the FSA has set
voluntary salt reduction targets for 85 categories of processed foods,
which are to be achieved by 2010. For example, breakfast cereals should
contain no more than 0.8g salt/100g and bread no more than 1.0g
salt/100g^93^.

It is the first time in any country that a government agency in the
world has set the salt content for such a wide range of processed foods.
As a result of this the UK is first country in the world to have a
coherent, systematic, ongoing reduction of the salt content of nearly
all foods to which salt has been added by the food industry.

To-date the progress that has been achieved is very encouraging. Many of
the leading retailers (supermarkets) have salt reduction plans in
progress and are reducing the salt contents of their foods. For example
one of the major supermarkets in the UK announced in 2006 that over the
past five years they had removed over 1000 tonnes of salt from their
own-label food products, stating that "the average weekly shop could now
have less than 24% less salt than exactly the same basket of groceries
did a year earlier"^94^. Since this announcement salt reduction has been
extended too many other products.

Additionally, many of the major brand manufacturers, e.g. Kelloggs,
Heinz, Unilever, have reduced the salt concentration of their foods. A
number of caterers are also working towards the salt targets. For
example, McDonalds has reduced the amount of salt in its products by
between 14% and 75% and is continuing to make further reductions^95^.

Looking at individual food categories the results are also very
positive. There have been significant reductions across a broad range of
product categories that included everything from bread and breakfast
cereals to soups and meal sauces. For example a survey revealed that the
average salt level of ready meals on sale in UK supermarkets has reduced
by 45% over the last four years. In fact, 84% have already reached the
FSA's 2010 targets for salt content^96^.

2.  **Consumer awareness campaign**[]{#__RefHeading___Toc194484174
    .anchor}

At the same time, there has been a huge consumer awareness campaign
including adverts on the television, in the tabloids, on buses, on
posters and in magazines. The campaign has been run in 3 stages. The
first stage was to raise awareness that too much salt is bad for health.
Stage 2 alerted adults to the fact that they should be consuming no more
than 6g salt per day. The main messages of the final stage focused on
the fact that 75% of salt consumed comes from processed foods and
therefore consumers should check the labels and choose lower salt
options. Several million pounds has been spent on this advertising
campaign. Since the start of the campaign the FSA has carried out
research to track the progress of the campaign. They have found that the
number of people aware that they should be eating no more than 6g salt
per day rose from 3% to 34% in just one year. Similarly, there has been
a rise in the number of people making an effort to reduce their salt
intake.

3.  **Working with third sectors
    partners**[]{#__RefHeading___Toc194484175 .anchor}

The advertising campaign targets the general population, however there
are a number of high risk groups within the population, i.e. blacks and
Asians, that the FSA has identified. They have provided grants to
partner organizations to complement the advertising campaign to
establish projects to lower salt intake in these population sub-groups.

**Success of the UK salt reduction
strategy**[]{#__RefHeading___Toc194484176 .anchor}

The UK public health campaign to reduce salt intake is already working.
The average daily salt intake in the adult population of the UK has
fallen from an average of 9.5 grams in 2001 to 9.0 grams by March
2006^97^. Although this might not seem like a significant change
previous studies had shown that the UK was increasing its salt intake,
so this marks the beginning of the reversal of an increasing trend.
Additionally, it is likely that salt intake has fallen further since
2006 as many more processed foods have had their salt content reduced
since 2006.

**Finland**[]{#__RefHeading___Toc194484177 .anchor}

Finland was one of the first countries to implement population-wide
initiatives to decrease the intake of salt in the whole population. This
began in the early 1970s and has resulted in a decrease by a third in
the average intake of salt in the Finnish population during the past 30
years^57^.

Due to the fact that over 75% of salt intake in Finland comes from
processed foods there has been a lot of emphasis put on the food
industry to develop reduced --salt food products. Since the 1980s many
food companies have reduced the sodium content of their food products by
replacing conventional table salt with a sodium-reduced, potassium- and
magnesium-enriched mineral salt known as Pansalt. Such products,
including even McDonald's hamburgers, can display a "Pansalt" logo.

In the early 1990s to further encourage the food industry to lower the
salt content of their food products The Ministry of Trade and Industry
and the Ministry of Social Affairs and Health, set new salt labelling
legislation for all the food categories which make a substantial
contribution to the salt intake of the Finnish population. Foods that
are high in salt are required to carry a "high salt content" warning.
Additionally, if a food product contains a low level of salt the food is
allowed to display a low salt label.

In combination with the food industry efforts there has also been a
public awareness programme on the harmful effects of salt on health.

These different measures have resulted in a substantial reduction in the
average salt intake of the Finnish population since the 1970s.
Accompanying this reduction in salt intake there has been a reduction of
over 10mmHg in both systolic and diastolic blood pressure and a
corresponding decrease of 75-80% in both stroke and coronary heart
disease mortality^56^. Since both body mass index and alcohol
consumption have increased during this period, this can largely be
explained by the reduction in salt intake. A reduction in fat intake and
an increase in potassium intake via the use of reduced-sodium, potassium
and magnesium-enriched salt and an increased consumption of fruit and
vegetables have also contributed to the fall in cardiovascular disease.

**Other countries**

[]{#__RefHeading___Toc194484178 .anchor}

Other countries are now following the example of the UK and Finland and
are developing a strategic plan to lower salt intake in their
population. For example in Ireland, a nutrition committee of the Food
Safety Authority of Ireland (FSAI) concluded, in 2005, that the
scientific evidence supports a link between salt intake and raised blood
pressure^98^. Subsequently the FSAI set the goal to reduce salt intake
in the population from 10 g/day to 6 g/day. The strategic approach
includes consumer awareness efforts, as well as action by the food
industry to lower the salt content of their food products, where to-date
substantial reductions have been made in the salt content of food.

In Canada there is increasing concern and realisation about the harmful
effect of too much salt on health, and in 2006 the first Canadian Chair
in Hypertension Prevention and Control was appointed, whose major
priority is to reduce the amount of salt added to food by the food
industry in the following 5 years. The Chair is supported by a number of
health related organizations as well as scientists. Together they will
lobby the government and public food sector for policies to reduce the
addition of salt to food. Already the food industry is attempting to
reduce salt in foods. For example a number of whole grain bread products
have had their salt levels reduced by 25 per cent.

Additionally, due to the success of the UK salt reduction strategy,
AWASH (Australian Division of World Action on Salt and Health), in 2007,
launched a national campaign to lower the salt intake of the Australian
population to 6g/day by 2012. The main objectives of the campaign known
as Drop the Salt! are to lower salt in food by 25%, increase consumer
awareness about the benefits of a low salt diet and promote clear
labelling of foods that makes the salt content immediately apparent to
the consumer.

Many other countries are stepping up their activity. In the Netherlands
the dietary guidelines were revised in 2006 stating that salt intake
should be reduced to 6g/day^99^. The Dutch Consumer Organisation
(Consumentenbond) has also initiated a number of activities to raise
awareness about the harmful effect of too much salt on health. In
addition, both the French Food Standards Agency (AFFSA) and the Swedish
Food Standards Agency have now considered the evidence and have a
programme in place for reducing the salt content of food in both France
and Sweden in a similar way as in the UK.

It is surprising that the U.S. is far behind many other developed
countries when it comes to salt reduction. In the U.S. there has been
consistent advice to reduce salt intake since the 1980s from current
intakes to 6 grams/day. In January 2000 a large meeting was organized by
the National Heart, Lung and Blood Institute in Washington where all of
the evidence on salt was reconsidered. There was representation both
from the food industry and Salt Institute. The conclusion of this
meeting was that \"Americans consume more sodium than they need and a
population wide strategy of reducing salt in the food supply is an
important public health strategy that can lower blood pressure among
populations\"^100^. More recently in 2007, The American Medical
Association (AMA) published a report calling for a major reduction in
the salt content of processed and restaurant foods^101^. The AMA also
pressed the FDA to cease the rule that allows salt and its component
sodium to be treated as \"generally recognized as safe\". However,
despite these recommendations in the U.S., little action has been taken.

# Labelling

# 

The AMA has also urged that the FDA to improve requirements for the
labelling of sodium on processed food products^102^.

Clear labelling of the salt content of foods is essential for the
consumer to easily identify whether a food is high in salt so that an
informed decision can be made about the purchase of the item. The UK
Food Standards Agency are introducing a front-of-pack signpost labelling
system which has now been accepted by most of the major supermarkets,
where there will be a colour coding of green, amber and red for salt,
fat and sugar. This type of labelling enables consumers to see at a
glance whether a product has a little or a lot of salt. If, for example,
the salt content is colour coded as red this instantly informs the
consumer that the product contains a lot of salt, whereas, green shows
the food product contains a low level of salt. Consumer research has
shown that this is by far the most preferred way of labelling and has a
dramatic effect on the purchase of foods, particularly when they are in
the red category^103^.

The National Heart Foundation of New Zealand, in 1991, introduced a
front-of-pack labelling logo known as 'Pick the Tick'. Products that
meet a defined nutritional criteria can display the logo. 'Pick the
Tick' has effectively reduced the salt content of commonly consumed
foods by encouraging food manufacturers to develop and reformulate
products with a healthy nutrition profile so that they can obtain the
logo. It was shown that in a one-year period between July 1998 to June
1999, 'Pick the Tick' influenced bread, breakfast cereal and margarine
companies to exclude \~33 tonnes of salt through the reformulation and
formulation of their products^104^.

An informative at a glance food label system should be adopted by the
U.S., where it will make it much easier for consumers to choose
healthier low salt products as well as encourage food manufacturers to
market foods with lower levels of salt.

**Why are some members of the food industry so reluctant to reduce the
salt content of processed foods?**[]{#__RefHeading___Toc194484180
.anchor}

The preservative properties of salt were discovered by the Chinese
approximately 5,000 years ago and salt then became of great economic
importance as it was possible to preserve food during the winter and
allowed the development of settled communities. Salt was the most traded
commodity in the world, with intake reaching a peak around the 1870s.
However, with the invention of the deep freezer and the refrigerator
salt was no longer required as a preservative. Salt intake has been
declining but with the recent large increase in consumption of very
highly salted processed food, salt intake is now increasing to levels
similar to those of the 1870s.

The reasons that the food industry adds salt in such large amounts to
processed foods is mainly because it makes cheap, unpalatable food
edible at no cost. If high salt foods are consistently consumed, the
salt taste receptors are suppressed and habituation to high salt foods
occurs, with greater demand for profitable highly salt processed foods.
Food manufacturers often argue that the reason for the high salt content
of their products is due to consumer taste preferences, i.e. individuals
prefer these saltier products and if the salt content was lowered it
would lead to consumer rejection. However, one very important factor to
be considered is that as salt intake falls, the specific salt taste
receptors in the mouth become much more sensitive to lower
concentrations of salt and this adjustment takes only one or two months.
This means that lower concentrations of salt then taste as salty as the
previous higher concentrations. It is therefore very unlikely that the
lowering of salt concentrations in foods will lead to rejection of the
foods. Indeed, all of the evidence suggests that once salt intake is
reduced, individuals much prefer food with less salt and reject the
highly salted foods they ate previously. Consumer experience in the UK
has confirmed this, ie where salt has been reduced in major brand
products, there has been no reduction in sales and no complaints about
changes in taste.

Salt has two other important properties - one is in meat products where
increasing the salt concentration in conjunction with other water
binding chemicals increases the amount of water that can be bound as a
gel into the meat product and the weight of the product can be increased
by up to 20% with water. The other important property is that salt is a
major determinant of thirst and any reduction in salt intake will reduce
fluid consumption with a subsequent reduction in soft drink and mineral
water sales^82,\ 105^. For instance, a 6 gram reduction in salt intake
in the United States would lead to a reduction in soft drink sales of
approximately 20 billion 250ml cans per year. Some of the largest snack
companies in the world are part of companies selling soft drinks. Salt
manufacturers and extractors also have a major interest in the salt used
in processed foods as approximately 40% by value of their sales of salt
go to the processed food industry (Figure 17).

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  ![](media/image17.wmf){width="4.957638888888889in"
  height="3.6104166666666666in"}

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**Figure 17.** The commercial importance of salt in processed food.

It is therefore not surprising that the salt industry and some members
of the food industry, particularly those that have soft drink or mineral
water connections, are very reluctant to see any reduction in salt
intake.

However, the fact is that nearly all food companies in the UK, many of
which are multi-national, have now accepted the very strong evidence
linking salt and blood pressure with other harmful effects and are
agreeing to slowly reduce the salt concentrations of their foods.

# 

# Conclusion

The evidence that relates dietary nutrients, such as salt, potassium,
saturated fat, fruit and vegetables, to blood pressure has to rely on
weighing all of the findings from various types of research studies -
epidemiological, migration, intervention, treatment trials as well as
animal studies. When all of the evidence is considered, the evidence for
salt intake, particularly when judged against other nutrients appears to
be robust, and stronger than for other beneficial changes, e.g.
decreasing consumption of saturated fat, sugar or increasing fruit and
vegetable consumption. Furthermore, reducing salt intake is one of the
easiest intervention measures to implement as it does not require
consumers to change their dietary practices, but it requires the food
industry to make gradual and sustained reductions in the amount of salt
they add to food. Therefore, reducing salt intake is by far the most
practical and easiest change in the diet to implement.

It is obvious that the USA recognise the harmful effects of too much
salt on health, as demonstrated by the recommendations that salt intake
should be lowered to 6 g/day or less. So why then does it appear that
the FDA is continuing to ignore the evidence by allowing salt and its
component sodium to be "generally recognised as safe"? These
recommendations now need to be backed up with action to reverse the
trend of an increasing salt intake. The FDA needs to recognise that
salt, in the levels currently being consumed, is dangerous. The U.S.
should follow the lead of countries such as Finland and the U.K. who
have implemented a salt reduction strategy, and seen promising results.
A reduction in salt intake would result in a major improvement in public
health -- similar to the provision of clean water and drains in the late
nineteenth century in Europe. Furthermore, the USA, as the world
superpower, could act as an example for the rest of the world.

**References**[]{#__RefHeading___Toc194484182 .anchor}