A survey of iodine nutrition status of Tianjin residents between 2002 to 2011 and analysis of suitable iodine content in salt

Objective To investigate the consumption status of iodized salt and iodine nutrition status of Tianjin residents,and to provide a scientific basis for iodine supplementation.Methods Sampling methods:① Salt iodine:According to "The National Project of Surveillance on IDD",the iodine in salt samples from 18 Tianjin districts (counties) was tested between 2002 to 2011.②Iodine nutritional status of children:Investigation of iodine nutritional status of children was conducted four times in 2002,2005,2009 and 2011.In 2002 and 2005,two primary schools were selected in each district.By age,gender parity principle,40 subjects aged from 8 to 10 in each school were randomly selected to perform thyroid examination and 20 of them were selected to collect urine samples for determination of urinary iodine.In 2009,according to their sub-area positions in the north,the south,the east,the west and the center of each district,5 primary schools were selected in each town (if there were less than five towns in the district,all towns had been selected).Twenty subjects aged from 8 to 10 in each school were selected to collect urine samples for determination of urinary iodine.In 2011,probability sampling method (PPS) was used to select 30 primary schools,and then 40 children aged from 8 to 10 were randomly selected in each school to examine thyroids.At the same time,urine samples from 12 children of the 40 selected children were tested.③Iodine nutritional status of women of childbearing age:In 2007,2008 and 2010,150,50 and 60 women of childbearing age were selected in Hangu District,urine samples of them were collected for determination of urinary iodine.④Iodine nutritional status of pregnant and lactating women:In 2011,3 towns around each primary school were selected.Five pregnant and five lactating women were selected in each town,urine samples of them were collected for determination of urinary iodine.Test methods:①Salt iodine was tested by direct titration,while Sichuan salt and other reinforced edible salt by arbitration determination based on the "General Test Method in Salt Industry-Determination of Iodide Ion" (GB/T 13025.7-1999).②Thyroid was tested by B-type-ultrasound and judged according to "Diagnostic Criterion of Endemic Goiter" (WS 276-2007).③Urinary iodine was tested by the "Method for Determination of Iodine in Urine by As3+-Ce4+ Catalytic Spectrophotometry" (WS/T 107-2006).Results From 2002 to 2011,the consumption rate of qualified iodized salt,the rate of qualified iodized salt,the coverage rate of iodized salt,the rate of non-iodinated salt was 92.7％(43 489/46 926),97.4％(43 489/44 694),95.1％ (44 694/46 926) and 4.8％(2273/46 926),respectively.The median salt iodine was in the range of 29.2-36.7 mg/kg.Children's urinary iodine was monitored 4 times,the median urinary iodine was 228.0,221.5,191.8; and 194.7 μg/L,respectively.Children goiter rates were 2.1％(27/1258),1.6％(19/1186) and 2.1％(26/1219) of the 3 times monitored.The median urinary iodine in pregnant and lactating women was 145.2 and 136.0 μg/L.The median urinary iodine in women of childbearing age was 130.7,196.1 and 229.5 μg/L,which increased with the increase of coverage of iodized salt.Conclusions The iodine nutrition of Tianjin residents,women of childbearing age and lactating women are at appropriate level.The iodine nutrition of pregnant women is lower than appropriate level.Recommended salt iodine level in our city is 30 mg/kg,or 25 mg/kg for ordinary residents,and 30 mg/kg for pregnant women. Key words: Iodine; Urine; Salts ; Goiter