National iodine deficiency disorders: an analysis of surveillance data in 2011

Abstract

Objective s To understand current situation in national prevention and control of iodine deficiency disorders (IDD), and to evaluate the progress in eliminating IDD in 31 provinces and Xinjiang Production and Construction Corps (Corps) in China. Methods In 2011, 30 units were sampled in each of 31 provinces and Corps in China based on the sampling method of Probability Proportional to Size. After excluding townships of water iodine level higher than 150 μg/L, 1 primary school was chosen in each unit, by the randomized sampling method, 40 students in each school were sampled for examining their thyroid volume, among them, 12 students were tested for their urinary iodine level and for their household salt iodine level and per capital daily salt intake. Near the location of these primary schools, 3 townships were chosen, 5 pregnant women and 5 lactating women in each township were sampled to test their urinary iodine level. Besides, 1 water sample was sampled according to the location in each village (east, west, south, north, and middle) in non-central water supplying villages, and 2 tap water samples in central water supplying villages. The ultrasound was used to detect goiter size according to the diagnostic criteria for endemic goiter; As3+-Ce4+ catalytic spectrophotometry using ammonium per sulfate digestion (WS/T 107-2006) was used to test the urinary iodine level; the testing method recommended by the National Iodine Deficiency Disorders Reference Lab was applied to test the water iodine level, the direct titration method among the generic methods of iodide testing for salt production industry (GB/T 13025.7-1999) was used to determine the salt iodine level; and the arbitration method was adopted for quantitative determination in case of well salt or special salts and the salt intake was estimated based on three-day weighed food record. Evaluation standards are as follows: urinary iodine level of children: deficient is the median of urinary iodine (MUI) less than 100 μg/L, adequate is MUI at 100-199 μg/L, more than adequate is MUI at 200-299 μg/L, and excessive is MUI equal to or greater than 300 μg/L; salt iodine: definition of qualified iodized salt is (35 ± 15) mg/kg; non-iodized salt (GB 5461-2000) is iodine less than 5 mg/kg; definition of unqualified iodized salt is iodine between 5-< 20 mg/kg or higher than 50 mg/kg. The total population of the sixth national census was used for statistical data correction. Results Among 31 provinces and Corps, children's goiter rate was 2.4%, which was obviously lower than the IDD elimination standard at the national level (< 5%); the national iodized salt coverage rate was 98.0% and the consumption rate of qualified iodized salt was 95.3%, both figures had achieved the national standard (the iodized salt coverage should be greater than 95% and the consumption rate of qualified iodized salt greater than 90%). The median of salt iodine was at 30.2 mg/kg; the MUI of children, pregnant women and lactating women was 238.6, 184.4 and 174.4 μg/L, respectively. Urinary iodine of children was higher than adequate level, of both pregnant women and lactating women were at adequate level. The surveillance results of water iodine in 25 provinces revealed that the median was at 5.6 μg/L; the salt intake surveillance results among students' households in 24 provinces and the Corps revealed that the daily intake was 10.1 g per person a day. Conclusions National IDD prevention and control strategy integrated with universal salt iodization as a key measure has achieved remarkable impacts. IDD has been eliminated at the national level. Key words: Iodine; Deficiency disorders; Children; Women; Urinary; Salts; Epidemic studies