ASSOCIATION BETWEEN DIETARY IODINE INTAKE AND PREVALENCE OF SUBCLINICAL HYPOTHYROIDISM IN THE COASTAL REGIONS OF JAPAN

The prevalence of thyroid dysfunction in relation to iodine intake was studied in adults (n = 1061) in five coastal areas of Japan that produce iodine-rich seaweed (kelp). The prevalence of hyperthyroidism (TSH < 0.15 mU/L) was similar in these areas, whereas that of hypothyroidism (TSH > 5.0 mU/L) varied from 0-9.7%. The relative frequency of above normal iodide concentration in the morning urine (greater than or equal to 75 mu mol/L) [high urinary iodide (UI)] varied from 3.7%-30.3%. Together with previously reported results of a noncoastal city, the frequency of high UI correlated significantly with that of hypothyroidism with negative thyroid autoantibody (r = 0.829, n = 6, P < 0.05) but not with positive thyroid autoantibody (r = 0.278, NS) or with that of hyperthyroidism (r = 0.038, NS).