Selenium deficiency is very rare in the United States and Canada, where intakes even in low-selenium regions are well above the RDA. Keshan disease, a heart muscle disease, occurred in parts of China with very low soil selenium, and deficiency is also associated with Kashin-Beck disease, a joint disease in low-selenium and low-iodine areas. In North America, groups at higher risk include people on long-term kidney dialysis and people living with HIV.
Common symptoms
On its own, selenium deficiency rarely causes illness, but it produces biochemical changes that can predispose to illness under added stress
Keshan disease, a heart muscle disease, in severe deficiency in parts of China
Kashin-Beck disease, a type of osteoarthritis that starts in childhood, in low-selenium and low-iodine regions
Can worsen iodine deficiency, raising the risk of congenital hypothyroidism in infants
At-risk groups
People in countries whose diet comes mainly from vegetables grown in selenium-poor soils, such as parts of China
People undergoing long-term kidney dialysis
People living with HIV
Vegans in some European countries where average intakes are low
Note: Brazil nuts are very high in selenium (about 68 to 91 mcg per nut), so one or two can exceed the 55 mcg RDA
When to see a doctorSelenium deficiency is very rare in North America, so testing matters mainly for people on long-term dialysis or living with HIV; a doctor can measure plasma or serum selenium. Selenium has a narrow safety margin: chronic intake above 400 mcg a day can cause hair loss, brittle nails, garlic breath and nervous system symptoms, so do not supplement above that without medical advice.