Selenium

Essential for thyroid hormone conversion, immune defence, and reducing oxidative stress during treatment.

What it is

Selenium is an essential trace mineral and the key component of selenoproteins, including glutathione peroxidase — the body's primary enzymatic antioxidant system. Selenium deficiency is very common in Central and Eastern Europe due to selenium-poor soils. Selenase (sodium selenite) is the pharmaceutical form used in European oncology.

Why it matters

Selenium is critical for thyroid hormone conversion (T4→T3 via selenoprotein deiodinase), immune function (NK and T-cells), DNA repair (via thioredoxin reductase), and sperm quality. In oncology, low selenium status correlates with increased cancer risk and worse treatment outcomes. Sodium selenite is used in German oncology centres to reduce radio- and chemotherapy toxicity.

The evidence

A landmark randomised trial (Clark et al., 1996, JAMA) found selenium supplementation reduced total cancer mortality by 50% and incidence of several cancers in deficient populations. Selenase IV infusions are a standard adjunct in some German cancer centres for reducing radiotherapy mucositis. Serum selenium testing is strongly recommended before starting.

This information is for educational purposes and does not constitute medical advice. Always discuss supplement use with your care team, particularly if you are undergoing active cancer treatment.

Dosing

100–200mcg/day. Selenomethionine for general use (best bioavailability and safety profile). Sodium selenite preferred in oncology for more direct antioxidant activity. Total intake from all sources should not exceed 400mcg/day.

Cautions

Selenium has a narrow therapeutic window. Toxicity (selenosis) occurs above 400mcg/day total and causes hair loss, nail brittleness, and neurological symptoms. Test serum selenium before starting — deficiency and toxicity both cause harm. Avoid combining high-dose selenium with other strong antioxidants during certain chemotherapy protocols.