Also called ascorbic acid, vitamin C is necessary for the growth and repair of tissue, wound healing, and the health of cartilage, bones, and teeth. It is a powerful antioxidant, meaning that it neutralizes potentially harmful free radicals in our bodies. It is water-soluble, and the body can store only small amounts. Thus, humans must consume vitamin C on a regular basis. Many fruits and vegetables are rich in vitamin C, especially citrus fruits, peppers, broccoli, strawberries, and cantaloupe.

Claims, purported benefits: Vitamin C supplements, especially in high doses, prevent or cure colds; may help prevent cancer, heart disease, and cataracts and other vision problems, or any of the other chronic conditions thought to be a result of free radical damage.

Bottom line: There’s no evidence that megadoses of vitamin C prevent or cure cancer or colds. In spite of the thousands of studies, the only certainty is that vitamin C prevents scurvy and plays other basic roles in human health. An intake of 75 to 90 milligrams daily appears to be all you really need. More does not seem to be better, except in the case of smokers—and then only an extra 35 milligrams is needed. If, however, you eat nine servings of fruits and vegetables daily, as we recommend, you’ll get far more vitamin C—probably 200 to 500 milligrams a day. There’s no evidence you need this much, but such a diet will also supply many other nutrients that, all together, will help keep you healthy and may reduce your risk of cancer and heart disease. In other words, in striving to consume more vitamin C, you’ll improve your diet. Supplementation is not necessary or recommended.