| [Background]Iodine is a necessary microelement for the human body, which is one of the essential elements to synthesize thyroxine.Iodine deficiency or excess may cause negative effect on human body.Iodine excess exists in more than ten provinces in China.There are about 30,000,000 people living in iodine excess areas,mainly in six provinces, including Jiangsu,Shandong,Shanxi,Anhui,Henan and Hebei,where drinking water is the most common source of high iodine intake.Surveys in these provinces indicated that the rate of endemic goiter was very high.[Objective]To explore the relationship between thyroid diseases and excessive iodine intake from drinking water.[Methods and Subjects]Two townships were selected at random and surveyed.Iodine excess township had a median water iodine concentration of 1,284.1μg/L where the median urinary iodine concentration of 8～10 years old child was 1,961.0μg/L,and the iodine normal township has a median of 77.9μg/L in the drinking water where the median urinary iodine concentration of 8～10 years old child was 255.1μg/L.Thyroid conditions of all residents in the two townships were assessed clinically.The prevalence of thyroid diseases was assessed. [Results]The registered population of iodine excess township was 27,006 among which 8,890 people migrate temporally to other place for a job and 18,116 people stayed home.Out of 18,116 people,96.4 percent were surveyed.While the registered population of iodine normal township was 20,756 among which 13,446 people stayed home.Out of 13,446 people,94.9 percent were surveyed.The age and sex composition either of the people migrating out for a job or of the people staying home between the two townships were comparable.Nine kinds of thyroid diseases were identified in this survey,such as endemic goiter,hyperthyroidism,sub-clinical hyperthyroidism, hypothyroidism,sub-clinical hypothyroidism,thyroiditis,thyroid cist, thyroid benign tumor and thyroid malignant tumor.606 dwellers in iodine excess township were diagnosed any kind of thyroid diseases and the prevalence was up to 346.86 per 10,000,2.38 times higher than that in iodine normal township.Higher prevalence was found across age groups in iodine excess township.The prevalence of thyroid diseases was 2.74 times higher among females than males in the iodine excess township, which compares 3.68 times in the iodine normal township.As following was the order of thyroid diseases proportion in the iodine excess township:endemic goiter(57.69%),sub-clinical hyperthyroidism(14.92%),thyroiditis(13.23%),hypothyroidism(8.92%), hyperthyroidism(4.00%),thyroid benign tumor(0.62%),sub-clinical hyperthyroidism(0.42%)and thyroid malignant tumor(0.15%).The following was the order of the iodine normaltownship's:thyroid goiter(49.74%),thyroiditis(16.06%),hyperthyroidism(13.99%), sub-clinical hyperthyroidism(7.77%),thyroid benign tumor(5.18%), thyroid cyst(4.66%)and hypothyroidism(2.59%).Fifty-eight people in iodine excess township were diagnosed having hypothyroidism and its prevalence was 33.20 per 10,000,which is 8.47 times higher than that in iodine normal township.Higher prevalence of hypothyroidism was found across age groups in iodine excess township. The prevalence of hypothyroidism was 12.95 per 10,000 among males in the iodine excess township,which compares 8.81 times in the iodine normal township.The prevalence was 56.05 per 10,000 among females in the iodine excess township,which was 8.33 times higher than that in the iodine normal township.The prevalence of hypothyroidism among females was much higher than that among males either in the iodine excess township or in the iodine normal township.Ninety-seven patients suffering from sub-clinical hypothyroidism were found in the iodine excess township and its prevalence was 55.52 per 10,000.While the number in the iodine normal township was 15 and the prevalence was 11.75 per 10,000.Higher prevalence of sub-clinical hypothyroidism was found across age groups in iodine excess township. The total prevalence in the iodine excess township was 4.73 times higher than that in the iodine normal township.The prevalence of sub-clinical hypothyroidism was 18.35 per 10,000 among males in the iodine excess township,which compares 3.22 times in the iodine normal township.The prevalence was 97.48 per 10,000 among females in the iodine excess township,which was 5.27 times higher than that in the iodine normal township.The prevalence of sub-clinical hypothyroidism among females was much higher than that among males either in the iodine excess township or in the iodine normal township.Twenty-six people suffering from hyperthyroidism were found in the iodine excess township with a prevalence of 14.88 per 10,000.While the number in the iodine normal township was 27 and the prevalence was 21.15 per 10,000,which was much higher than that in the iodine excess townthip.The prevalence of hyperthyroidism among females in the iodine excess township was 23.15 per 10,000,which was much lower than that in the iodine normal township.No difference was found in prevalence among males between the two townships.The prevalence of hyperthyroidism among females was much higher than that among males either in the iodine excess township or in the iodine normal township. Eighty-six people were diagnosed having thyroiditis in iodine excess township and its prevalence was 49.22 per 10,000,which was 2.02 times higher than that in the iodine normal township where 31 patients were found and the prevalence was 24.29 per 10,000.No difference was found in prevalence among males between the two townships.However the prevalence among the females in the iodine excess township was up to 96.26 per 10,000,which was much higher than that in the iodine normal township.The prevalence of thyroiditis among females was much higher than that among males either in the iodine excess township or in the iodine normal township.The median of TPOAb from 251 healthy people's serum was 5.20μ/ml in the iodine excess township.The median of TPOAb from 105 healthy people's serum in the iodine normal township was 7.46/ml,which was much higher than that in the iodine excess township.The median of TGAb all was10μ/ml and no difference was found in the distribution of TGAb.Three hundred and seventy five people suffering from goiter in the iodine excess township were diagnosed,whose thyroid function did not change. While the number in the iodine normal township was 96.The prevalence of goiter in the iodine excess township was up to 214.64 per 10,000, which was 2.85 times higher than that in the iodine normal township. Higher prevalence was found across age groups in iodine excess township.The prevalence of goiter was 147.88 per 10,000 among males in the iodine excess township,which compares 3.48 times in the iodine normal township.The prevalence was 290.00 per 10,000 among females in the iodine excess township,which was 2.57 times higher than that in the iodine normal township.The prevalence among females was much higher than that among males either in the iodine excess township or in the iodine normal township.Of the 256 healthy people from iodine excess township,the median of TSH was 3.54 mμ/L,which was significantly higher than that in iodine normal township(the median of TSH was 2.58 mμ/L of 108 dwellers). The FT3(mean±SD)was 5.08±0.78pmol/L in iodine excess township and it is 5.14±0.76 in iodine normal township.No difference was found in FT3 between the two townships.The FT4(mean±SD)was 14.97±2.59pmol/L in iodine excess township and it is 14.55±1.85pmol/L in iodine normal township.No difference was found in FT4 between the two townships too.Among these people,43 sub-clinical hyperthyroidism patients were diagnosed in iodine excess township(the positive rate was 16.80%)and the number in iodine normal township was 8(the positive rate was 7.41%).The positive rate in the iodine excess township was significantly higher than that in the iodine normal township.[Discussion and Conclusions]Compared with iodine normal township,iodine excess township has higher prevalences of major thyroid diseases with a different order of major thyroid diseases,implying iodine excess may have altered the composition of thyroid diseases with increased prevalence of thyroid diseases.The following epidemiological features were observed,a)the prevalence of major thyroid diseases is as high as 346.86 per 10,000,which is 2.4 times higher than that in iodine normal township,The prevelance was observed consistently elevated across different age groups with 10-20 years age having the highest prevalence,b)The prevalences of goiter, sunclinical hypothyroidism,hypothyroidism and autoimmune thyroiditis are higher in iodine excess township than those in iodine normal township.c)Of the residents in the iodine excess township,goiter, sub-clinlical hypothyroidism,hypothyroidism and thyroidism were the first four diseases in the thyroid diseases constitution.While in the iodine normal township,it were goiter,thyroidism,hyperthyroidism and sub-clinlical hypothyroidism respectively.d)Chronic excessive iodine intake did not increase the hyperthyroidism,more research is still required to confirm if excessive iodine intake lowers hyperthyroidism,e) Potentially dysfunctional pituitary-thyroid axis is observed to be higher in iodine excess township than that in iodine normal township. |
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