Selenium Supplement Role Unclear in Autoimmune Thyroiditis

Miriam E Tucker

December 28, 2016

Selenium supplementation appears to reduce circulating thyroid autoantibodies in patients with chronic autoimmune thyroiditis (AIT), but the data do not support routine use of selenium supplementation in the absence of deficiency, new research suggests.

Findings from a systematic review and meta-analysis were published in the December issue of Thyroid by final-year medical student Johanna Wichman and colleagues, Odense University Hospital, Denmark, and University of Southern Denmark, Odense.

Overall, data from 11 controlled trials show that selenium supplementation reduces serum thyroid peroxidase autoantibody (TPOAb) levels at 3, 6, and 12 months and thyroglobulin autoantibody (TgAb) levels at 12 months in patients treated with levothyroxine (LT4). In patients not receiving LT4, supplementation was associated with decreases in both TPOAb and TgAb levels after 3 months, but not after 6 or 12 months.

"Our research question was whether or not selenium can decrease autoantibody levels. The answer to that question seems to be that it can. However, thyroid autoantibodies are first and foremost a diagnostic criterion in AIT. After the diagnosis, the levels are a surrogate marker of disease activity at the most. Therefore, we don't think the effects we report warrant routine selenium supplementation," study coauthor Kristian Hillert Winther, MD, PhD, of the department of endocrinology, Odense University Hospital, told Medscape Medical News.

In fact, in a recent separate meta-analysis, Dr Winther and colleagues found no effect of selenium supplementation on thyroid-stimulating hormone, health-related quality of life, or thyroid ultrasound in individuals not yet receiving LT4 (Endocrine. 2016; DOI:10.1007/s12020-016-1098-z). Moreover, there were insufficient data to assess clinically relevant outcomes in LT4 substitution–treated patients.

Yet, despite the lack of evidence for benefit of selenium supplementation in AIT, a recent survey found that a majority of endocrinologists in Italy were prescribing it (Eur Thyroid J. 2016;5:164-170). "Interestingly, selenium supplementation is used despite not being mentioned in the international guidelines (Eur Thyroid J. 2016;5:149-151) for the management of hypothyroidism," Dr Winther commented.

But he added, "We think moderate to severe selenium deficiency should be corrected when observed, irrespective of AIT."

Effect on Antibodies Found, but Clinical Implication Unclear

A total of 16 controlled trials involving 1494 AIT patients were included in the systematic review, and 11 trials involving 687 patients were included in the meta-analysis.

Among LT4-treated patients, those assigned to receive selenium had significantly lower TPOAb levels at 3 months in seven studies (P < .0001), after 6 months in three studies (P < 0.001), and after 12 months in one study (P < .0001). Study quality was rated moderate at months 3 and 6, but low at 12 months.

Among newly diagnosed patients who had not yet received LT4 treatment, those receiving selenium also had significantly lower TPOAb levels at 3 months in three studies (P < .0001), but not after 6 or 12 months. Evidence quality was moderate at 3 months, and very low and low at 6 and 12 months, respectively.

In the LT4-treated group, TgAb levels were significantly decreased at 12 months among those receiving selenium in one study (P < .0001), but not at 3 months in six studies (P = .85) or 6 months in three studies (P = .12). Here, the evidence quality was low or very low at all time points.

And in the group not yet treated with LT4, TgAb significantly decreased with selenium at 3 months in two studies (P = .027), but not at 6 months in 3 studies (P = .218) or at 12 months in two studies (P = .174). The quality of evidence was moderate at 3 months, and low or very low at 6 and 12 months, respectively.

Across seven studies that included LT4-treated patients receiving selenium supplementation, TPOAb decreased 24% compared with 6% among controls, a significant difference (P = .02).

Adverse effects were five times more common (relative risk, 4.96) in selenium-treated patients, especially gastric discomfort. Headache and skin rash were also more common in the selenium group, and hair loss occurred equally in both selenium and placebo patients. There were no serious adverse events, signs of acute toxicity, or hospitalizations. Here, evidence quality was high.

"We don't know yet if [selenium supplementation] offers any benefit to patients with autoimmune thyroiditis. Future well-powered randomized clinical trials evaluating outcomes such as disease progression or health-related quality of life are warranted," Dr Winther said.

The Odense team is currently conducting a randomized double-blind placebo-controlled trial of selenium supplementation as an adjuvant to LT4 in AIT patients. The primary outcome is health-related quality of life.

The authors have reported no relevant financial relationships.

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Thyroid. 2016;26:1681-1692. Article

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