ABSTRACT
Objective To examine the relationship between hyperthyroidism and excessive iodine intake from drinking water through epidemiological studies in the iodine excess and the iodine normal villages. Methods Mengzhuang village of Pei county and Xingji village of Pizhou city in Jiangsu province, with median water iodine concentration of 1284.1 μg/L and 77.9 μ/L, respectively,were selected in 2006. Thyroid diseases of all local residents in the two villages were assessed clinically to compare the prevalence and the distribution of hyperthyroidism. Results A total of 17 471 residents were recruited from the iodine excess village, 26 of them were diagnosed with hyperthyroidism. The prevalence of hyperthyroidism was 1.49‰, 0.75‰ (7/9264) in male,2.32‰( 19/8207) in female, and the age-standardized prevalence was 1.48‰. A total of 12 765 residents were recruited from the iodine normal village, among them 27 residents were diagnosed with hyperthyroidism. The prevalence of hyperthyroidism was 2.12‰, 0.96‰(7/6823) in male, 3.26‰(20/5942) in female, and the agestandardized prevalence was 2.02‰. The prevalence and age-standardized prevalence was significantly lower in the iodine excess village than those in the iodine normal village (u = 2.88, 2.89; all P < 0.01). The prevalence of hyperthyroidism was lower among females in the iodine excess village (2.32‰) than that in the iodine normal one (3.37‰, u = 2.89, P < 0.01). Residents aged 20 - 50 years had higher prevalence of hyperthyroidism[(19.36 -38.96 )/10 000]in the two villages. The proportion of Graves diseases was 50.00% (13/26) in the iodine excessvillage, higher than that in the iodine normal village[29.41%(5/17) , χ2 = 5.853, P < 0.01]. Conclusions Chronic excessive iodine intake does not increase the chance of suffering from hyperthyroidism. On the contrary, the prevalence of hyperthyroidism in the iodine excess village decreases significantly compared with that of the iodine normal village. The prevalence is higher among females.