The effect of iodine supplementation on status and cognition in iodine deficient young adults

Abstract

Iodine is needed for brain development, which continues until the fifth decade of life, thus a lack of iodine in the diets of young adults could impair cognition. This was a randomized, double blind study of iodine deficient adults (n=205) aged 18–30 years who consumed 150 μg of potassium iodate or placebo daily for 32 wk. Subjects provided a urine and blood sample, and underwent cognitive tests from the Weschler Adult Intelligence Scale before and after supplementation. The median urinary iodine concentration (MUIC) at baseline was 65 μg/L indicating that the subjects were mildly iodine deficient (i.e. MUIC of 50–100 μg/L). Iodine supplementation significantly improved MUIC to 115 μg/L (p<0.001) such that subjects had adequate iodine status (i.e. MUIC >100 μg/L), while those in the placebo group remained iodine deficient (MUIC of 79 μg/L). The median serum thyroxine concentration of 97 nmol/L fell within the normal reference range at baseline and was not affected by supplementation (p=0.561). There was no effect of iodine supplementation on cognitive test scores that assessed perceptual reasoning including block design (p=0.385), matrix reasoning (p=0.364), and visual puzzles (p=0.675), or working memory including digit span backward (p=0.474) and letter‐number sequencing (p=0.408). This is the first study to suggest that mild iodine deficiency has no adverse consequences on cognition in young adults.