Myths vs facts: Selen and fatigue

Selenium is an essential trace mineral critical for selenoproteins (e.g., glutathione peroxidases) that protect against oxidative stress and support thyroid hormone metabolism. Myth: 'Selenium deficiency is a common cause of fatigue.' Fact: Overt deficiency is rare in most Western populations; fatigue is more often due to other causes (iron, sleep, stress, thyroid). Myth: 'Selenium supplements boost energy for everyone.' Fact: Supplementation only benefits individuals with confirmed low selenium status. In replete individuals, extra selenium does not reduce fatigue and may cause toxicity (selenosis) above 300 µg/day. Evidence: human-observational studies show links between low selenium and fatigue in deficient populations, but RCTs in non-deficient adults show no consistent benefit. Genetic variants (e.g., rs3877899 in SEPP1) have small effects on selenium transport but are not clinically actionable. Bottom line: Don't self-supplement for fatigue without testing. Check thyroid, iron, vitamin D, and sleep first. Evidence level: human-moderate.