[An epidemiological survey of thyroid disorders in an area with high iodine content in water supply]

To investigate the status of thyroid disorders among people aged 14 years and older residing in Huanghua County, an iodine excess intake area in north China.

4,230 people were asked to fulfill the questionnaire and 1,074 among them aged (36.97 +/- 12.83) years were accepted to be samples for the test. All subjects who were taken as samples needed to fill the questionnaire on thyroid disorders in detail, accept physical and ultrasound examination. Their morning fasting urine were collected for measurement of iodide concentration, and their sera were measured for thyroid-stimulating hormone(TSH, the third generation), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) and thyroglobulin (TG). If some people had abnormal TSH level, their free T4, free T3 and TSH receptor antibody(TRAb) were measured.

The median level of urinary iodide of the sample subjects was 614.61 micrograms/L. The prevalence of clinical and subclinical hyperthyroidism was 1.21% and 1.12% respectively; 92.3% of the clinical hyperthyroidism were of Graves' disease and 75% of the subjects with subclinical hypothyroidism were TRAb positive. The average incidence of clinical hyperthyroidism was not different between 2 periods before and after general iodinization of table salt in this area (1991-1995 and 1996-2000). The prevalence of clinical and subclinical hypothyroidism was 1.96% and 6.05% respectively. All the clinical patients were female, among them 85.71% were TPOAb and/or TGAb positive, while only 29.23% of the subclinical patients were TPOAb and/or TGAb positive. Positive TPOAb and TGAb were seen in 11.6% and 9.3% respectively of the sample subjects with an age-related increase. Positive thyroid autoantibody was more common in the female and those with abnormal TSH. The prevalence of thyroid cancer during the period of 1994-2000 was 91.58/100,000.

The high prevalence of hypothyroidism and thyroid cancer indicates that excessive iodine intake in this area is not safe.