Selenium

Selenium is incorporated into selenoproteins, including glutathione peroxidase (GPx) and thioredoxin reductase — enzymes that neutralise reactive oxygen species and protect cells from oxidative damage. In skin specifically, selenium supports UV damage repair, modulates inflammatory responses, and may protect against some forms of skin cancer.

The critical nuance with selenium is the U-shaped dose-response curve: both deficiency and excess are harmful. Selenium has a narrow therapeutic window, and supplementation is only beneficial when baseline status is inadequate. Unlike some minerals where more is simply excreted, selenium toxicity (selenosis) is a real concern at chronic intakes above 400mcg daily.

• Antioxidant defence through glutathione peroxidase support
• UV damage protection (when combined with other antioxidants)
• May reduce skin cancer risk in deficient populations
• Immune function support relevant to skin infection resistance
• Possible improvement in inflammatory skin conditions when deficiency is corrected

RDA: 55mcg daily for adults. This is achievable through diet for most people.

Supplementation range: 50–200mcg daily if dietary intake is low. Do not exceed 200mcg from supplements.

Upper tolerable limit: 400mcg daily (combined dietary and supplemental). Chronic intake above this causes selenosis — hair loss, nail brittleness, GI distress, fatigue, and neurological symptoms.

Best dietary source: A single Brazil nut contains approximately 70–90mcg selenium. Two Brazil nuts daily provides more than adequate selenium without any supplement.

Testing: Serum selenium can be measured to assess status before supplementing. This is recommended before starting high-dose supplementation.

Preferred: Selenomethionine — the organic form with the best absorption and most consistent research.

Acceptable: Selenium yeast (which contains a mix of organic selenium forms). Sodium selenite is the inorganic form, with lower bioavailability.

Simplest approach: 2 Brazil nuts daily provides highly bioavailable selenium at an ideal dose without supplementation.

Oral selenium and topical antioxidants (vitamin C, vitamin E): Selenium supports the glutathione system — one of the body’s internal antioxidant networks. Topical antioxidants work locally in the skin. Adequate selenium status ensures the systemic antioxidant network is functioning, which complements the local protection provided by topical antioxidants.

The SeLECT trial caution: The Selenium and Vitamin E Cancer Prevention Trial (SELECT) found that selenium supplementation at 200mcg daily did NOT reduce skin cancer risk in selenium-adequate populations. This underscores that supplementation only helps when there is a deficiency to correct.

With sunscreen: Selenium supports UV damage repair but does not replace sun protection. As with astaxanthin and omega-3, think of it as supporting the cellular repair systems that handle UV damage that gets past sunscreen.

• Supplementing without checking dietary intake — most people get enough from food
• Taking high-dose selenium (200mcg+) without testing baseline status
• Combining a selenium supplement with a multivitamin that also contains selenium (double-dosing)
• Eating large quantities of Brazil nuts daily (easy to exceed safe limits — 2 per day is sufficient)
• Assuming more antioxidant supplementation is always better — selenium has a clear toxicity threshold

Clark et al. (1996): The Nutritional Prevention of Cancer (NPC) trial found 200mcg selenium daily reduced non-melanoma skin cancer risk by 25% and overall cancer mortality by 50% — but subsequent analysis revealed benefits were limited to those with LOW baseline selenium. Selenium-adequate participants showed no benefit and possible harm. (JAMA)

Lippman et al. (SELECT, 2009): Large trial (35,000+ men) found 200mcg selenium daily did NOT reduce prostate or skin cancer risk in selenium-adequate populations. Established that selenium supplementation is only beneficial when correcting deficiency. (JAMA)

Rayman (2012): Comprehensive review of selenium and health, establishing the U-shaped dose-response relationship and emphasising that supplementation should target the narrow window of adequacy (85–120mcg daily intake), not maximise intake. (The Lancet)