Selenium

How strong is the research?

Trials in 389 women with PCOS tested selenium. Weight, BMI, cholesterol and insulin resistance were all unchanged. One antioxidant measure improved a little.

1 paper read, 1 against.

Tested as: Most trials gave 200 mcg a day. The review did not tell the two forms apart, which is a real weakness.

Who was studied: 389 women with PCOS across several trials, mostly Iranian. Their selenium levels were not reported.

We found 1 study on this. We have not finished reading them yet, so we are not ready to say either way.

How much to take

200 mcg

Before you take it

• NIH ODS Tolerable Upper Intake Level (UL) for selenium is 400 mcg/day for all adults (ages 14+); EFSA (2023) set a more conservative UL of 255 mcg/day for all adults based on evidence linking chronic excess intake to hair loss and nail changes.
• The primary clinical signs of chronically high selenium intake (selenosis) are hair loss and nail brittleness or loss; NIH ODS explicitly names these as the most common manifestations of selenium toxicity, not deficiency.
• Average US dietary selenium intake is approximately 100–150 mcg/day; supplemental doses of 100–200 mcg/day may approach or exceed the EFSA UL (255 mcg/day) in individuals with higher dietary selenium from food or geography, without the user being aware.
• Individuals in high-selenium geographic regions (parts of the US Great Plains — South Dakota, Nebraska, Wyoming) may have dietary intakes near or above the NIH UL before any supplementation is added.
• Drug interaction: cisplatin and platinum-based chemotherapy agents reduce selenium concentrations in hair and serum; selenium supplementation during chemotherapy may affect cisplatin efficacy; patients on these agents must consult their oncologist before supplementing.
• Selenium form substantially affects bioavailability and tissue retention: selenomethionine (organic) is retained longer and accumulates more in tissues than sodium selenite (inorganic) or selenium-enriched yeast; the same supplemental dose carries meaningfully different toxicity profiles depending on the form.
• In thyroid patients on levothyroxine, selenium is a cofactor for iodothyronine deiodinase enzymes that convert T4 to active T3; supplementation may alter thyroid hormone metabolism and should be disclosed to the prescribing clinician.
• Selenium supplementation above the RDA (55 mcg/day) is not recommended during pregnancy without confirmed deficiency; excessive selenium is teratogenic in animal models.
• A 2008 US outbreak documented 201 individuals developing alopecia, nail changes, and neurological symptoms from a commercial selenium-containing supplement; the product contained approximately 200 times its labeled selenium amount, demonstrating the real-world toxicity risk from over-the-counter selenium products.

When to take it

Best taken: with food