💊 What it does
Selenium is a trace mineral that functions primarily as a component of selenoproteins — a family of enzymes involved in antioxidant defence (glutathione peroxidase), thyroid hormone metabolism, immune function, DNA synthesis and repair, and reproductive health. It works synergistically with iodine in thyroid function. Low selenium is associated with increased oxidative stress, impaired thyroid function, and weakened immunity.
👤 Who needs it
People in selenium-depleted regions — UK and European soils are notably low in selenium compared to North America. Vegans and plant-based eaters whose intake depends on soil selenium content of plant foods. Anyone with thyroid conditions (selenium is critical for T4 to T3 conversion). People with malabsorption conditions.
🥦 Food sources first
Brazil nuts are by far the richest source — just 2 nuts provide approximately 90–180 µg (the variability reflects where the trees were grown). Other plant sources include sunflower seeds, mushrooms, lentils, tofu, oats, and brown rice. However, selenium content of plant foods varies enormously with soil content — UK-grown crops are generally low. Brazil nuts from Bolivia and Brazil tend to be much richer than those from other regions.
🗓 When to supplement
When dietary intake is low and food-source selenium is unreliable (particularly in the UK). When thyroid function is impaired. A blood selenium test can confirm status before supplementing.
🏷 Best form to look for
Selenomethionine (organic selenium) is the best-absorbed form. L-selenomethionine specifically is well studied. Sodium selenite (inorganic) is also effective but less well retained. Avoid selenium-enriched yeast if you have yeast sensitivities.
⏰ When to take it
Can be taken at any time with or without food. Consistent daily timing is more important than specific timing.