Endocrine Abstracts

Both humic substances (HS) and iodine may influence the thyroid gland. Tap water is a major source of iodine intake in some areas, where iodine has been shown to be bound in HS.

We investigated tap water and old subjects from two areas with and without iodine bound in HS in tap water, to assess their importance for urinary iodine excretion and for the thyroid. Analysis of tap water, measurement of iodine in urine and thyrotropin (TSH), thyroid peroxidase antibody (TPO-Ab) and thyroglobulin (TG) in serum from old people living in Skagen and Randers, Denmark were done. Thyroid disease, medication, smoking, and alcohol and vitamin use were evaluated with questionnaires. Average tap water iodine content in Randers/Skagen was 2.0/140 μg/L. The 430 participants were 130/82 women/men aged 78 years in Randers, and 134/84 aged 75–80 years in Skagen.

Median (25; 75 percentiles) urinary iodine content of spot urine samples from participants not taking vitamins was 42 (28; 58) μg/L in Randers and 146 (116; 206) μg/L in Skagen (P<0.001). TSH <0.4 mU/l was more frequent (17.1% vs. 3.9%, P<0.001), and TSH >3.6 mU/l slightly less frequent (7.0% vs. 12.3%, P=0.074) in Randers than in Skagen, without gender differences (P=0.18). TPO-Ab were present in serum in 27.9% women and 8.7% men (P<0.001) with no difference with areas (P=0.87), smoking habits (P=0.11), alcohol use (P=0.40) or use of iodine in supplements (P=0.77). Among TPO-Ab positive subject, the level tended to be higher among women than among men (495 vs 201, P=0.09). TG-Ab were present in serum in 37.1% (88) of women and 22.9% (36) of men (P=0.003). Serum TG was markedly higher in Randers compared to Skagen dwellers (14.8 vs. 7.7, P<0.001).

In conclusion, iodine in drinking water is bioavailable despite binding to HS, and HS do not corrupt iodines influence on the thyroid gland.