Selenium

Selenium is a vital trace element, symbol Se. Too little can trigger Keshan disease, a deadly cardiomyopathy, and possibly raise cancer risk, while excess causes balding, garlic breath, intestinal distress, and impaired mental functioning. Food sources include seafoods, meat, and some grains and seeds, though content varies with soil selenium. Both deficiency and excess are real public-health concerns. Soil maps help predict where deficiency may occur. Supplements should be used with care. Balance is everything with trace elements. Brazil nuts are famously rich in it, with a single nut sometimes exceeding the daily requirement.