Minerals

Selenium

A trace mineral with outsized impact on thyroid and immune health.

~15% of the global population is selenium-deficient; rates vary by region due to soil content

Why it matters for longevity

Selenium is critical for thyroid hormone metabolism, antioxidant defense via glutathione peroxidase, and DNA repair. Low selenium levels are linked to increased cancer risk, impaired immune function, and cognitive decline. The SU.VI.MAX trial found that selenium supplementation reduced cancer incidence in men by 31%.

How much you need

RDA

55mcg for adults

Optimal

Researchers suggest 100-200mcg daily, though exceeding 400mcg can be toxic.

Signs you might be low

  • Weakened immune function
  • Thyroid problems or fatigue
  • Hair thinning or loss
  • Mental fog or difficulty concentrating

Best food sources

FoodPer serving
Brazil nuts (1 nut)96mcg
Yellowfin tuna (3 oz)92mcg
Halibut (3 oz)47mcg
Sardines (3 oz)45mcg
Turkey breast (3 oz)31mcg

Key research

Rayman MP (2012). Selenium and human health. The Lancet, 379(9822), 1256-1268.

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