title: Association between dietary iodine intake and prevalence of subclinical hypothyroidism in the coastal regions of Japan.
abstract: 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 (> or = 75 mumol/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). Hypothyroidism was more prevalent in thyroid autoantibody-negative subjects with high UI (group II, 12.1%) than with normal UI (group I, 2.3%) (P < 0.001). The TSH [21.9(6.5-73.7)mU/L] (mean +/- SD) and thyroglobulin [288 (182-456) micrograms/L] levels in group II were significantly higher than the respective levels in group I [9.6(3.7-25.3)mU/L and 123 (38-399) micrograms/L] (P < 0.05). Free T4 of group II (9.9 +/- 3.9 pmol/L) was significantly lower than in group I (14.2 +/- 3.9 pmol/L) (P < 0.05). These results indicate that 1) the prevalence of hypothyroidism in iodine sufficient areas may be associated with the amount of iodine ingested; 2) hypothyroidism is more prevalent and marked in subjects consuming further excessive amounts of iodine; and 3) excessive intake of iodine should be considered an etiology of hypothyroidism in addition to chronic thyroiditis in these areas.
authors.affiliation: Department of Internal Medicine, Hokkaido Central Hospital for Social Health Insurance, Sapporo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Konno
authors.forename: H
authors.initials: H
authors.lastname: Makita
authors.forename: K
authors.initials: K
authors.lastname: Yuri
authors.forename: N
authors.initials: N
authors.lastname: Iizuka
authors.forename: K
authors.initials: K
authors.lastname: Kawasaki
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D004032:Diet; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000139:chemically induced / Q000453:epidemiology*; D007454:Iodides / Q000652:urine; D007455:Iodine / Q000008:administration & dosage* / Q000009:adverse effects; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D013972:Thyrotropin / Q000097:blood
chemical_list: D007454:Iodides; D013972:Thyrotropin; D007455:Iodine