Introduction: In 2017 and 2018, the national investigation of drinking water iodine distribution was carried out in China. Thirty-one provinces, 2,936 counties and 40,325 townships were investigated. There were 33716 (83.6%) townships with median water iodine (MWI) <10μg/L; 5559 (13.8%) townships with MWI between 10μg/L and 100μg/L; and 1050(2.6%) townships with MWI>100.0μg/L. According to the Chinese standard, areas with WI<10μg/L are the endemic areas of iodine deficiency disorders, and areas with WI>100μg/L are the water-borne iodine-excess areas, what about areas of WI between 10μg/L and 100μg/L? An investigation were conducted in six provinces concerning relationship between population iodine nutrition, thyroid function and thyroid disease in different water-iodine regions.
Methods: Totally, 4665 adults, 2098 children and 403 pregnant women were enrolled in areas with different water iodine levels, <10μg/L, 10-19μg/L, 20-29μg/L, 30-39μg/L, 40-49μg/L, 50-59μg/L, 60-69μg/L, 70-79μg/L, 80-89μg/L, 90-99μg/L and 100-150μg/L. Urinary iodine（UI）, WI, thyroid function and volume were measured.
Results: With the increase of WI, the UI of adults, children and pregnant women showed an increasing trend. When WI >100μg/L, the MUI of adults exceeded 300μg/L and the MUI of pregnant women exceeded 250μg/L. After data fitting, u-shaped curves were presented between WI and the abnormal rates of TSH, FT4, TgAb and TPOAb, goiter rate and thyroid nodule rate, separately. Comparing to WI in other range, the UI of adults, children and pregnant women were all in the appropriate ranges, abnormal rates of TSH, FT4, TPOAb and TgAb, goiter rate, thyroid nodule rate were all lower when the WI was in 40~ 100μg/L by comprehensive analysis.
Conclusions: When the WI was in 40 ~100μg/L, the main indexes were basically in suitable range, hence, those areas can be considered as the iodine adequate areas.