How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Iodine
An essential trace element for the production of thyroid hormones. Supplementation serves to correct a deficiency: without a deficiency, studies find nothing for it to add.
Benefits
- Corrects mild deficiency in adults: 150 µg per day for 24 weeks restored iodine status and lowered thyroglobulin, the marker for an iodine-deficient thyroid (randomized trial)
- During pregnancy, 200 µg per day improves iodine status and maternal thyroid hormones, with the best results when supplementation begins before or at the very beginning of pregnancy (meta-analysis)
- In deficient children, improves cognition: 150 µg per day for 28 weeks improved two reasoning tests, and the Cochrane review of eight trials concludes there is a slight cognitive gain and less hypothyroidism
- In iodine-deficient overweight women, 200 µg per day for 6 months lowered TSH and reduced total cholesterol by 11% in those who had high levels
Precautions
More is not better: in adults with normal thyroid function, 400 µg per day in addition to diet, or about 800 µg in total, was enough to trigger subclinical hypothyroidism, and a meta-analysis associates chronic excess iodine with more overt and subclinical hypothyroidism in adults. If you have a thyroid condition or are on thyroid medication, do not take it without medical advice. The limits: in only mildly deficient pregnant women, 200 µg per day improved neither IQ nor motor development in children followed up to 5-6 years of age, and two meta-analyses find no effect on the growth or cognitive development of infants; in moderately deficient elderly individuals, 80 µg per day corrected the deficiency without changing TSH or free T4.
Recommended dosage
150 µg per day in adults, the reference intake set by EFSA; 200 µg per day during pregnancy and breastfeeding. The selected trials tested from 80 to 200 µg per day. Count the iodine from your diet and iodized salt before adding any.
Did you know?
In only mildly deficient pregnant women, 200 µg of iodine per day changed nothing in the IQ of children measured at 5-6 years of age: the effect of iodine on the brain is seen where the deficiency is more pronounced.
What the studies say
This systematic review and meta-analysis reveals that iodine supplementation is a beneficial strategy to prevent iodine deficiency during pregnancy. A daily dose of 200 µg of iodine can improve urinary iodine status and maternal thyroid hormone concentrations. The best results are obtained when supplementation begins before or early in pregnancy.
Candido AC, Azevedo FM, Silva DLF, Ribeiro SAV, Castro Franceschini SDC. — Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS) (2023) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more