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Selenium, an essential trace element, has dose-dependent health effects. Its role in immune function and disease susceptibility is debated, prompting investigation into its supplementation as a public health measure.

Objectives

This study systematically reviews and meta-analyzes experimental studies on selenium supplementation’s impact on immunity-related outcomes in healthy individuals.

Methods

A comprehensive search of PubMed/MEDLINE, Embase, and clinicaltrials.gov was conducted up to October 17, 2022. A meta-analysis compared immunity-related outcomes between selenium-supplemented and control groups, utilizing a dose–response approach when possible.

Results

Nine trials, conducted in North America and Europe with durations from 8 to 48 weeks, were included. Both inorganic and organic selenium forms were examined. Selenium supplementation did not significantly affect immunoglobulin or white blood cell concentrations. Dose–response analysis showed that plasma selenium levels above 100 μg/L did not further enhance IgA levels or T cells. An inverted U-shaped relationship was observed for NK cell count, with lower counts below and above 120 μg/L. The sole beneficial effect was increased NK lysis activity, though dose–response analysis was not feasible. Cytokine levels remained largely unaffected by selenium supplementation.

Conclusions

The data suggest some beneficial effects of selenium on immune function, but overall findings are inconsistent and heterogeneous due to variations in trial duration and interventions, with evidence of null and even detrimental effects. This systematic review concludes that selenium supplementation beyond the recommended dietary intake does not yield significant benefits for immune function.

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