Selenium — Forms, Dosage & Interactions

Selenium is an essential trace mineral that functions primarily through incorporation into selenoproteins — a diverse family of at least 25 proteins critical to antioxidant defence, thyroid hormone metabolism, immune function, and fertility. Unlike most nutrients, selenium's biological activity is mediated almost entirely via these selenoproteins, with selenocysteine serving as the functional amino acid at their active sites. Despite being required only in microgram quantities, deficiency carries significant health consequences, and insufficiency is more prevalent in the UK than is often appreciated. Research suggests that UK dietary intakes frequently fall below the NHS Reference Nutrient Intake, largely due to the selenium-poor nature of UK soils. People supplement selenium primarily to support thyroid function, bolster antioxidant capacity, and maintain healthy immune responses. There is also ongoing research interest in selenium's role in male and female fertility and in cardiovascular health. The overall evidence base is rated as strong for thyroid support and antioxidant function. Studies indicate that benefits are most pronounced in individuals who are deficient or insufficient at baseline; those already replete may see limited additional gain from supplementation. Individual responses may vary considerably depending on dietary habits, baseline selenium status, and the supplement form used.