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
55mcg for adults
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
Key research
Rayman MP (2012). Selenium and human health. The Lancet, 379(9822), 1256-1268.
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