Selenium

Selenium yeast (S. cerevisiae), mainly as L-selenomethionine (C₅H₁₁NO₂Se)

Evidence: Strong

Selenium is an essential trace element and a key component of selenoproteins, which have antioxidant and anti-inflammatory properties. Its role in reducing oxidative stress can indirectly benefit the gut by mitigating inflammation and supporting the overall health and immune response of the gastrointestinal tract.

There are 47,702 peer-reviewed scientific studies on this ingredient.

Selected Study 1/2:

Wang, Y., Wu, Y., Chen, T., Wu, X., Yuan, W., Zhu, Q., Wang, X., & Zi, C. (2024). Selenium and Selenoproteins: Mechanisms, Health Functions, and Emerging Applications. Molecules, 30(3), 437. https://doi.org/10.3390/molecules30030437

Study Summary:

Study type: This paper is a 2025 narrative review that synthesizes current laboratory and clinical literature on selenium (Se) and selenoproteins; it enrolls no new participants but surveys dozens of pre-clinical studies and human trials across antioxidant, immune, endocrine, cardiometabolic and neuro-protective endpoints.

Observed benefits: The authors report that organic Se—especially when delivered as Se-enriched foods or selenoproteins—improves antioxidant defense, modulates immunity, lowers inflammation, supports glycemic and lipid control, protects the cardiovascular and nervous systems, enhances fertility and shows potential adjunct value against cancers and COVID-19.

Mechanisms of action: Key benefits derive from the 25 human selenoproteins that incorporate the Se-containing amino acid selenocysteine; these enzymes (e.g., glutathione peroxidases, thioredoxin reductases) neutralize reactive oxygen species, regulate redox-sensitive signaling, control thyroid hormone activation and fine-tune innate and adaptive immunity.

Organic forms such as selenomethionine are efficiently absorbed and converted to selenocysteine, while Se-enriched functional foods create a safe reservoir of bioavailable selenium for steady selenoprotein synthesis.

Side effects: The review notes that Se-enriched foods and organic selenomethionine have “low toxicity,” making them preferable for long-term supplementation, whereas high doses of inorganic selenite or selenate can be toxic; no serious adverse events are reported for nutritional doses, but the authors stress the need to monitor intake to avoid excess.

Strength of evidence: Biological plausibility is strong, and multiple human studies show correlations between adequate Se status and better health outcomes; however, clinical RCTs are still relatively small and heterogeneous, so the evidence supporting specific disease-preventive claims is moderate. The authors call for larger, well-controlled trials to clarify optimal dosing, long-term safety and the precise roles of less-studied selenoproteins.