Evidence

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

• Cancer. Eating a diet rich in fruits and vegetables might lower your risk of many types of cancer, such as breast, colon and lung cancers. However, it's not clear whether this protective effect is related to the vitamin C content in the food. Taking oral vitamin C supplements doesn't appear to offer the same benefit.
• Common cold. Taking oral vitamin C supplements won't prevent the common cold. Evidence also shows that the benefits of regularly taking vitamin C supplements to reduce the duration or severity of a cold are minimal.
• Eye diseases. Taking oral vitamin C supplements in combination with other vitamins and minerals seems to prevent age-related macular degeneration (AMD) from worsening. Some studies also suggest that people who have higher levels of vitamin C in their diets have a lower risk of developing cataracts.