Selenium
Selenomethionine · Foundation
An essential trace mineral with an unusually narrow window between too little and too much.
What the evidence says
Essential for thyroid hormone metabolism and antioxidant enzymes, and correcting deficiency matters — but frank deficiency is uncommon on Western diets. The large SELECT trial tested it for prostate cancer prevention and not only failed, it reported a higher diabetes signal in the selenium arm. Supplementing beyond need has repeatedly failed to help and occasionally hurt.
What studies used
Requirements sit near 55 mcg/day; the tolerable upper limit is about 400 mcg. Published studies had not established a preferred timing.
Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.
Watch out for
- Genuinely toxic in excess — hair and nail loss, garlic breath, neuropathy; the gap between adequate and harmful is smaller here than for almost any other mineral
- Stacking a multivitamin, a dedicated selenium product and selenium-rich foods is how people reach the upper limit without noticing; nut selenium content varies enormously by soil
Evidence base
established literature
Large human evidence base: several phase 3 or 4 trial reports, plus multiple meta-analyses or systematic reviews.
This letter measures how much human research exists, not whether it works for you — the tier above (Moderate) is the read on quality.
Research (12)
- Selenium and human healthLancet · 2012
- Selenium and thyroid diseasesFront Endocrinol (Lausanne) · 2023
- Selenium and Selenoproteins in HealthBiomolecules · 2023
- Regulation of Selenium Metabolism and TransportAnnu Rev Nutr · 2015
- Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and MetabolismInt J Mol Sci · 2023
- Selenoprotein S maintains intestinal homeostasis in ulcerative colitis by inhibiting necroptosis of colonic epithelial cells through modulation of macrophage polarizationTheranostics · 2024
- SeleniumNovartis Found Symp · 2007
- SELENOK-dependent CD36 palmitoylation regulates microglial functions and Aβ phagocytosisRedox Biol · 2024
- Dietary selenium and selenoprotein functionMed Sci Monit · 2012
- Selenium in Endocrinology-Selenoprotein-Related Diseases, Population Studies, and Epidemiological EvidenceEndocrinology · 2021
- Comparison of Sodium Selenite and Selenium-Enriched Spirulina Supplementation Effects After Selenium Deficiency on Growth, Tissue Selenium Concentrations, Antioxidant Activities, and Selenoprotein Expression in RatsBiol Trace Elem Res · 2024
- Mammalian selenium-containing proteinsAnnu Rev Nutr · 2001
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