Do selenium, iodine or thyroid supplements help?

Three different products get grouped under thyroid supplements, and they carry three different levels of risk. Selenium has a weak evidence base and low harm. Iodine has no benefit for most people in the United States and real potential for harm. Thyroid support blends are the dangerous category, because several contain actual thyroid hormone that is not declared on the label.

Selenium

Selenium is used by the enzymes that convert T4 to T3, which is the biological rationale. The Cochrane review of selenium supplementation in Hashimoto's thyroiditis included four trials with 463 participants over a mean of 7.5 months. None of the studies addressed health-related quality of life, which was the review's primary outcome. Selenomethionine 200 mcg reduced anti-thyroid peroxidase antibodies in three studies, but the reviewers stated that the clinical relevance is unclear and that the evidence does not at present allow confident decision making. Antibody titres are not a treatment target in the first place.

Iodine

The United States has an iodine-sufficient food supply, so more iodine does not improve thyroid function and excess can trigger dysfunction in a susceptible gland. The American Thyroid Association gives the adult recommended intake as 150 mcg daily, 220 to 250 mcg in pregnancy and 250 to 290 mcg during breastfeeding, and states that intake above 1,100 mcg daily may cause thyroid dysfunction. It advises against ingestion of iodine and kelp supplements containing more than 500 mcg of iodine daily for children and adults and during pregnancy and lactation, noting there is no known thyroid benefit to routine doses above the recommended daily allowance. The National Institute of Diabetes and Digestive and Kidney Diseases advises people with Hashimoto's to limit kelp, dulse and other seaweed.

Thyroid support products contain hormone

Kang and colleagues tested ten commercially available thyroid health supplements and found that nine of ten contained triiodothyronine and five contained thyroxine. The American Thyroid Association summary of that work concluded that the majority of the dietary thyroid supplements tested contained clinically significant amounts of thyroid hormones, and warned these could raise thyroid function tests and cause thyrotoxicosis with its attendant risks of arrhythmia and bone loss. Because these are sold as supplements, the hormone content is not on the label and there is no potency standard.

Bring every bottle to your appointment, including anything labelled for energy, metabolism or hair. If your TSH is suppressed and you take a thyroid support product, stop it and have thyroid function repeated in four to six weeks.