Vitamin C

Vitamin C is a substance the body needs to form blood vessels, cartilage, muscle and collagen in bones. The body also needs vitamin C for healing.

Also called ascorbic acid, vitamin C helps protect cells from damage. Substances like vitamin C that protect against cell damage are called antioxidants. The damage comes from molecules the body makes when it breaks down food, has contact with tobacco smoke, or is exposed to the sun's rays or other sources of harm.

These molecules are called free radicals. They may play a role in heart disease, cancer and other conditions. Vitamin C also helps the body absorb and store iron.

The body doesn't make vitamin C. It comes from the diet. Sources of vitamin C include berries, cantaloupe, tomatoes, peppers, potatoes, cabbage, Brussels sprouts, broccoli, spinach and citrus fruits, such as oranges. Vitamin C also comes as a supplement, mainly in the form of capsules you swallow and tablets you chew.

Most people get enough vitamin C from a good diet. Not having enough vitamin C, called deficiency, is more likely in people who:

• Smoke or are around secondhand smoke.
• Have certain conditions of the digestive tract or certain types of cancer.
• Have a diet that doesn't include enough fruits and vegetables.

Not having enough vitamin C can lead to a condition called scurvy. Scurvy causes anemia, bleeding gums, bruising and poor wound healing.

The recommended daily amount of vitamin C is 90 milligrams for adult men and 75 milligrams for adult women. If you take vitamin C for its antioxidant effects, the supplement might not be as good for you as natural vitamin C that's in food.

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.

Most people get enough vitamin C from a good diet. Vitamin C supplements might help people who are at risk of having a lack of vitamin C, called vitamin C deficiency.

When taken at suggested doses by mouth, vitamin C supplements are mostly safe. Taking too much vitamin C can cause side effects, including:

• Upset stomach, vomiting and loose stools.
• Heartburn.
• Stomach cramps or bloating.
• Tiredness and sleepiness or not being able to sleep, called insomnia.
• Headache.

In some people, oral vitamin C supplements may cause kidney stones. This mainly happens in people who take high doses of the supplements. Long-term use of oral vitamin C supplements over 2,000 milligrams a day raises the risk of serious side effects.

High doses of vitamin C can cause hemolytic anemia in people who have a condition called G6PDH deficiency, which is passed through families.

Before having medical tests, tell your healthcare professional that you take vitamin C supplements. High levels of vitamin C might affect the results of certain tests, such as blood sugar screening tests or stool tests for hidden blood, also called occult blood.

Vitamin C might react with the following:

• Aluminum. Taking vitamin C can make you take in more aluminum from medicines that have aluminum, such as phosphate binders. This can be harmful for people with kidney conditions.
• Chemotherapy. There is worry that use of vitamin C and other antioxidants during chemotherapy might keep chemotherapy medicines from working well.
• Estrogen. Taking vitamin C with birth control pills or hormone replacement therapy might raise estrogen levels.
• Protease inhibitors. Use of vitamin C might keep these antiviral medicines from working as well as they should.
• Statins and niacin. People with high cholesterol might take these medicines. Taking vitamin C with statins and niacin could keep the medicines from working as well as expected.
• Iron. Vitamin C makes the body absorb more iron. Getting more iron can be harmful for people who have a condition that causes too much iron in the body, called hemochromatosis.
• Warfarin (Jantoven). High doses of vitamin C might lower the body's response to this blood-thinning medicine.