What the research says

Research on the use of vitamin C for the following conditions shows:

• Cancer. Eating a diet rich in fruits and vegetables might lower the risk of many types of cancer, such as breast, colon and lung cancers. But it's not clear whether this effect is related to the vitamin C content in the food. Taking vitamin C supplements doesn't seem to affect cancer risk.
• Cardiovascular disease. Much research has focused on whether vitamin C supplements protect against heart disease. Taking supplements doesn't seem to affect heart disease risk.
• Common cold. Taking oral vitamin C supplements won't prevent the common cold. Studies show that taking vitamin C supplements has little effect on how long colds last or how bad they are.
• Eye diseases. Taking oral vitamin C supplements with other vitamins and minerals seems to keep age-related macular degeneration, also called AMD, from getting worse. AMD is a leading cause of vision loss among older adults. Some studies also suggest that people who have higher levels of vitamin C in their diets have a lower risk of getting cataracts.