Vitamin C (ascorbic acid) is a nutrient your body needs to form blood vessels, cartilage, muscle and collagen in bones. Vitamin C is also vital to your body's healing process.

Vitamin C is an antioxidant that helps protect your cells against the effects of free radicals — molecules produced when your body breaks down food or is exposed to tobacco smoke and radiation from the sun, X-rays or other sources. Free radicals might play a role in heart disease, cancer and other diseases. Vitamin C also helps your body absorb and store iron.

Because your body doesn't produce vitamin C, you need to get it from your diet. Vitamin C is found in citrus fruits, berries, potatoes, tomatoes, peppers, cabbage, Brussels sprouts, broccoli and spinach. Vitamin C is also available as an oral supplement, typically in the form of capsules and chewable tablets.

Most people get enough vitamin C from a healthy diet. Vitamin C deficiency is more likely in people who:

• Smoke or are exposed to secondhand smoking
• Have certain gastrointestinal conditions or certain types of cancer
• Have a limited diet that doesn't regularly include fruits and vegetables

Severe vitamin C deficiency can lead to a disease called scurvy, which causes anemia, bleeding gums, bruising and poor wound healing.

If you take vitamin C for its antioxidant properties, keep in mind that the supplement might not offer the same benefits as naturally occurring antioxidants in food.

The recommended daily amount of vitamin C is 90 milligrams for adult men and 75 milligrams for adult women.

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.

When taken at appropriate doses, oral vitamin C supplements are generally considered safe. Taking too much vitamin C can cause side effects, including:

• Nausea, vomiting and diarrhea
• Heartburn
• Stomach cramps or bloating
• Fatigue and sleepiness, or sometimes insomnia
• Headache
• Skin flushing

In some people, oral vitamin C supplements can cause kidney stones, especially when taken in high doses. Long-term use of oral vitamin C supplements over 2,000 milligrams a day increases the risk of significant side effects.

Tell your doctor that you're taking vitamin C supplements before having any medical tests. High levels of vitamin C might interfere with the results of certain tests, such as stool tests for occult blood or glucose screening tests.

Possible interactions include:

• Aluminum. Taking vitamin C can increase your absorption of aluminum from medications containing aluminum, such as phosphate binders. This can be harmful for people with kidney problems.
• Chemotherapy. There is concern that use of antioxidants, such as vitamin C, during chemotherapy might reduce the effect of chemotherapy drugs.
• Estrogen. Taking vitamin C with oral contraceptives or hormone replacement therapy might increase your estrogen levels.
• Protease inhibitors. Oral use of vitamin C might reduce the effect of these antiviral drugs.
• Statins and niacin. When taken with vitamin C, the effects of niacin and statins, which might benefit people with high cholesterol, could be reduced.
• Warfarin (Jantoven). High doses of vitamin C might reduce your response to this anticoagulant.