Also known as: Ascorbic acid.
Potential uses: Vitamin C is used to prevent cardiovascular problems, such as heart attacks and strokes, the breakdown of joint cartilage (osteoarthritis), and eye problems such as cataracts and macular degeneration. Vitamin C may help ease the length or severity of colds in some people. It also may play a role in lowering the risk for certain cancers, such as lung cancer and cancers of the digestive and gastrointestinal tract.
Usual dose: The recommended daily minimum intake of vitamin C is 75 milligrams per day for women and 90 milligrams per day for men. People who smoke should take 35 milligrams per day more than that. Between 250 milligrams per day and 1,000 milligrams per day is considered a reasonable dosage. This can come from foods and/or vitamin C supplements.
Are there any risks? Very high doses of vitamin C — more than 2,000 milligrams per day — can cause side effects such as diarrhea, gas, and stomach upset. Other risks include kidney damage and having too much iron in the blood. Vitamin C can interfere with blood thinners such as Coumadin (chemical name: warfarin). There are some concerns that large doses of vitamin C might reduce the effectiveness of certain cancer treatments, such as chemotherapy and radiation.
What does the research show? Although selected studies have found that women who consume higher amounts of vitamin C have a lower risk of breast cancer, research in general has not shown a strong connection. A recent review of 38 studies on vitamin C and cancer in general concluded that vitamin C cannot treat or prevent cancer. However, some studies have shown a connection between eating foods rich in vitamin C, such as fruits and vegetables, and reduced risk of breast cancer and other forms of cancer. Researchers are investigating whether vitamin C given intravenously, rather than orally, may be helpful in treating cancer.