Garlic, a member of the family that includes onions, leeks, and shallots, is native to Europe and Central Asia. An old Welsh saying goes, "Eat leeks in March and wild garlic in May, and all the year after physicians may play." Olympic athletes in ancient Greece chewed a clove at the start of a competition, believing it increased their stamina. Many cultures believed garlic had magical powers, including the ability to scare away vampires. Garlic's strong odor is due mostly to a sulfide called allicin. Garlic is a source of selenium, which must be present in the body for proper immune response, and which acts as an antioxidant in combination with vitamin E.