Study On Reasonable Iodine Concentration In Iodized Salt And Overall Intervention Strategy For Elimination Of Iodine Deficiency Disorders In A Mild Iodine Deficiency Area

Iodine is one of human body's necessary micronutrients. It is one of raw materials for synthesis of thyroid hormone which plays an important role in metabolism and development (both mental and physical) of human body. Lack of iodine in our body can lead to iodine deficiency disorders (IDD), which is characterized by retarded mental and physical development. Meanwhile, long excessively absorbed iodine may result in iodine excess disorders (IED). Today, after implementing Universal Salt lodization (USI) for many years, people get puzzled about the questions what is the adequate intake of iodine (AI), recommended dietary allowance (RDA) and tolerable upper intake level (UL), and if the present iodine content in iodized salt is optimal, not low or high.It is known to all that USI is the most effective policy to eliminate IDD, and gained giant success in our country. However, there are also many problems including the incidence of iodine-induced hyperthyroidism (IIH) and other diseases induced by iodization; endemic iodine-induced goiter in many areas caused by excessive iodine in drinking water of natural origin in our country; and ensurance of optimal iodine nutritional status of various populations. The present thesis tries to answer the above-mentioed questions by analyzing the existing surveillance data in China, conducting survey to compare the effectiveness on population indicators of iodized salt with different iodine contents, and geographic information analysis of iodine concentrations in drinking water in Jiangsu province. The present thesis provides additional evidence for adjustment of USI policy in China.Section One: Relationship between thyroid volume and urinaryiodine after 2-4 years of universal salt iodizationData from the 2nd and 3rd China national IDD surveillance were collected to analyze the tendency of thyroid volume (TV) variation, urinary iodine (UI) variation and the relationship between TV and UI among children aged 8-10 years in China after 2-4 years of universal salt iodization. The main results are presented as follows:1. Comparison of distributions in thyroid volume of children aged 8-10 years in 1997 and 1999.In 1997, the statistics of TV (ml) of 31343 children aged 8,9,10 years in China were 3.37 of mean, 3.27 of median, 2.85 of mode, 6.30 of 97% percentile. In 1999, the statistics of TV (ml) of 34545 children aged 8,9,10 years in China were 3.58 of mean, 3.45 of median, 3.16 of mode, 6.40 of 97% percentile. There was a significant difference ( x 2=382.0268, P<0.001 ) in the distribution. Significant difference was also found for Thyroid Volume calculated by age. The two rates of goiter between 1999 (8.49%) and 1997 (8.27%) measured by B-ultrasonography were not significantly different ( x2=1.408, P>0.05 ) .2. Comparison of distributions of urinary iodine concentrations of children aged 8-10 years in 1997 and 1999.The frequency distributions of urinary iodine concentrations of children aged 8-10 years in 1997's and 1999's were significantly different ( x2=336.7603, P<0.05 ) . In 1999, the mean of urinary iodine concentration (318.35ug/L) is lower than that in 1997 (343.80ug/L), but the median in 1999 (271.40ug/L) is slightly higher than that in 1997 (265.50ug/L). The number of sampling hits which urinary iodine concentrations were higher than 800ug/L in 1997 (5.87%) are more than those in 1999 (2.03%). This suggests that iodine nutrition in individualsin some provinces in 1997 were excessive. The medians of urinary iodine concentration in whole country except Tibet Province were above 100ug/L. But the number of sampling hits which urinary iodine concentrations were lower than 50u.g/L in some provinces are more than 20%. This phenomena indicated that there were still some people under the threat of IDD, and at the same time, some high urinary iodine concentration in 1997 and 1999 indicates that some districts in China in both years had risk of being excessive iodine nutrition.3. Relationship between thyroid volume and urinary iodineThe thyroid volume is uneve...