Studies have suggested that vitamin D may also have other uses. Studies have shown that low levels of vitamin D may increase the risk of heart attacks and deaths from some cancers. Other studies have shown that people with rheumatic diseases(风湿病)often have low levels of vitamin D.

　　专题二 │ 新题预测

　　The easiest way to get vitamin D is from sunlight. The ultraviolet rays react with skin cells to produce the vitamin. But many people worry about skin cancer and skin damage from the sun.

　　Darker skinned people produce less vitamin D than lighter skinned people. Production also decreases in older people and those living in northern areas that get less sunlight.

　　Not many foods naturally contain vitamin D．Foods with high levels include oily fish such as salmon, tuna and mackerel, and fish liver oils.

　　The researchers reported in 2007 that farmed salmon had a lot less vitamin D than wild salmon. 专题二 │ 新题预测

　　Small amounts of vitamin D are found in beef liver, cheese and egg yolks. And some people take dietary supplements containing the vitamin. But most of the vitamin D in the American diet comes from foods like milk with the vitamin added.

　　These days, more doctors are testing for vitamin D levels in their patients. But as research continues, some experts worry that if people take too much vitamin D, it might act as a poison. Also, skin doctors warn people to be careful with sun exposure. 专题二 │ 新题预测

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