Objective: In a follow-up study, we determined the prevalence, incidence, and natural course of positive anti-thyroperoxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TgAb) in the general population and examined the influences of iodine intake.

Design: The study was conducted in Panshan, Zhangwu and Huanghua, regions with mildly deficient, more than adequate, and excessive iodine intake, respectively. Of the 3,761 unselected subjects who were enrolled at baseline, 3018 participated in the five-year follow-up study. Serum TSH, TPOAb, and TgAb levels were measured.

Results: Among subjects in Panshan, Zhangwu and Huanghua, the prevalence of positive TPOAb was 11.23%, 11.83% and 12.02%, respectively, while 11.23%, 11.17% and 11.26% of subjects were TgAb positive, respectively. In the older population (45years), TgAb positive individuals were more frequent in Huanghua than Panshan and Zhangwu (P<0.05). The five-year cumulative incidence of positive TPOAb was 2.08%, 3.84% and 2.84% in Panshan, Zhangwu and Huanghua, respectively, while 2.91%, 3.64% and 5.07% of subjects were TgAb positive, respectively (P<0.05), corresponding to the increase in iodine intake. Subjects who were TPOAb and/or TgAb positive at baseline developed thyroid dysfunctions more frequently than those without antibodies (14.44% vs. 3.31%, P<0.01), there incidence of elevated TSH levels was 1.32%, 8.46%, and 15.38% in Panshan, Zhangwu, and Huanghua, respectively (P<0.05).

Conclusions: Subjects who were TPOAb and TgAb positive at baseline developed thyroid dysfunctions more frequently than seronegative subjects. High iodine intake was a risk factor for developing hypothyroidism in antibody positive subjects. A constant exposure to excessive iodine intake increased the incidence of positive TgAb.