Effect of selenium on thyroid autoimmunity and regulatory T cells in patients with Hashimoto's thyroiditis: A prospective randomized-controlled trial.

The short version

This randomised, open-label trial with 90 people who have Hashimoto's thyroiditis explored whether six months of selenium supplements changes the immune and thyroid markers of the disease. Hashimoto's thyroiditis is an autoimmune condition in which the immune system attacks the thyroid gland, measured through antibodies to thyroid peroxidase (TPOAb) and thyroglobulin (TGAb). Selenium is a trace mineral built into antioxidant proteins that the thyroid relies on, and regulatory T cells (Tregs) are immune cells that keep overactive immune responses in check, so the researchers also tracked these cells to see whether selenium acts through them. Conducted at a hospital endocrinology department in Nanjing, China, the study enrolled 90 adults with Hashimoto's who were not taking levothyroxine, about a third of them with mildly raised TSH (subclinical hypothyroidism). Forty-three took a 200 μg selenium-enriched yeast tablet daily for six months and 47 received no treatment, with both groups advised to keep iodine intake adequate. Blood and urine tests at baseline, three months and six months measured thyroid antibodies, thyroid hormones, selenium levels and Treg cells by flow cytometry. Selenium blood levels roughly doubled with the supplement (median 73.6 to 187.2 μg/L). By six months, TPOAb fell by 28.4 IU/ml in the selenium group while staying unchanged in controls (p = 0.001), TGAb fell by 48.8 IU/ml while rising by 18.3 in controls (p = 0.001), and TSH edged down (−0.16 mIU/L) while rising in controls (+0.48, p = 0.001). The largest TSH effect appeared in the 29 people with subclinical hypothyroidism (a fall of 2.5 mIU/L versus a rise of 1.91 in controls, p = 0.002). Activated Tregs were higher with selenium (13.19% vs 11.49%, p = 0.012), but the overall Treg percentage was not significantly different (p = 0.214). Free T3 and free T4 did not differ, and no adverse effects were reported. The authors suggest selenium may lower thyroid antibodies by raising antioxidant capacity and activated Tregs, with the greatest TSH benefit in subclinical cases. The evidence is limited: no placebo, open-label allocation, one hospital, a small sample, exploratory subgroup findings (interaction tests for selenium level were not significant), and only blood markers over six months, so symptoms, disease course and levothyroxine need were not assessed. The results apply only to people not taking levothyroxine, and the authors call for pre-specified trials.

Key findings

• In this open-label trial, 90 people with Hashimoto's thyroiditis (an autoimmune disease in which the immune system attacks the thyroid gland) who were not taking levothyroxine received either 200 μg/day of selenium-enriched yeast or no treatment for six months.
• After six months the selenium group had lower thyroid peroxidase antibody (TPOAb, a marker of the immune attack) by 28.4 IU/ml and lower thyroglobulin antibody (TGAb) by 48.8 IU/ml, while antibodies were unchanged or higher in the untreated group (both p = 0.001).
• TSH (thyroid-stimulating hormone, the pituitary signal that rises when the thyroid underperforms) fell by 0.16 mIU/L with selenium and rose by 0.48 mIU/L without it, with the largest fall in the 29 participants with subclinical hypothyroidism (−2.5 vs +1.91 mIU/L).
• Activated regulatory T cells (immune cells that dampen overactive immune responses) were higher with selenium (13.19% vs 11.49%, p = 0.012), which the authors propose as one mechanism.
• No adverse effects were reported, but there was no placebo, the trial was small and single-centre, and only blood markers were measured over six months.

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