Excess iodine intake may affect the development of Hashimoto's thyroiditis. Kelp consumption is very high in Okinawa. We expected a high prevalence of Hashimoto's thyroiditis in Okinawa. We studied urinary iodine excretion and the positivities of anti-thyroglobulin antibodies (TGAb) and anti-thyroid peroxidase antibodies (TPOAb) in the residents of Nishihara in Okinawa, Yamagata in Yamagata, Kobe in Hyogo, and Hotaka in Nagano, Japan. TGAb and/or TPOAb were positive in 142 (13.7%) of 1039 subjects in Nishihara, in 16 (16.0%) of 100 subjects in Yamagata, in 31 (13.4%) of 232 subjects in Kobe, and in 35 (13.9%) of 252 subjects in Hotaka; TGAb and/or TPOAb positivity was about the same in these 4 areas. One tenth of the subjects with positive TGAb and/or TPOAb had hypothyroidism; the frequencies of hypothyroidism in those with positive TGAb and/or TPOAb were about the same in Nishihara, Yamagata, Kobe, and Hotaka. The iodine concentration in samples of morning urine correlated well with the 24-h urine iodine excretion. The urinary iodine excretion was 1.5mg/day in Nishihara. There were no differences between Nishihara and Yamagata in the urinary iodine concentration, but the urinary iodine concentrations in Kobe and Hotaka were less than those in Nishihara or Yamagata. The amounts of iodine excretion in Kobe and Hotaka were moderate, and less than those in Nishihara or Yamagata. The amounts of iodine intake in Kobe and Hotaka were less than those in Nishihara or Yamagata, but TGAb and/or TPOAb positivity was about the same in Nishihara, Yamagata, Kobe, and Hotaka. The differences in dietary iodine intake do not affect TGAb and/or TPOAb positivity.
The Japan Endocrine Society