Vitamin C

Daily Value: 60 milligrams

Good Food Sources: Pineapple, broccoli, peppers, cantaloupe, strawberries, oranges, kiwifruit, pink grapefruit

Linus Pauling is gone--dead at the age of 93 from cancer. But at the Linus Pauling Institute of Science and Medicine in Palo Alto, California, and in research labs across the country, his scientific legacy lives on. Experts continue to investigate the healing potential of vitamin C, also called ascorbic acid.

"We're conducting research projects that explore the role of vitamin C in cardiovascular disease, cancer, HIV infection, cataracts, skin health and other physiological and pathological conditions," says Stephen Lawson, chief executive officer of the institute.

There's good reason to believe that further research will bear even more fruit. While skeptics continue to carp, already dozens of studies strongly suggest that vitamin C plays a role in preventing a variety of diseases. And there is a growing number of doctors who are using the nutrient to treat disease as well.

Vitamin C is thought to help protect the esophagus, oral cavity, stomach and pancreas--and possibly the cervix, rectum and breasts--from cancer. How does it do all of that?

Some forms of cancer are thought to be caused by what are called free radicals, naturally occurring renegade molecules that damage your body's healthy molecules (such as DNA, in the case of cancer) by stealing electrons to balance themselves. Vitamin C and other substances known as antioxidants neutralize free radicals by offering their own electrons, minimizing oxidative damage to DNA and other molecules, explains Balz Frei, Ph.D., associate professor of medicine and biochemistry at Boston University School of Medicine. Nitrites--potentially cancer-causing preservatives found in foods such as hot dogs and lunchmeats--and nitrates--found naturally in vegetables and drinking water--are also neutralized by vitamin C.

The long arm of vitamin C's antioxidant protection may also extend to heart health. In studies that looked at vitamin C and cholesterol levels, researchers found those who had high blood levels of vitamin C showed reduced risk of heart disease.

And in lab experiments, high concentrations of vitamin C have also been found to inhibit the growth of smooth muscle cells in artery walls. The abnormally high growth activity of these cells has been considered one of the initial steps in the development of cardiovascular disease, says Vadim Ivanov, Ph.D., head of the cardiovascular research program at the Linus Pauling Institute.

Vitamin C's role as an antioxidant may even help delay or prevent cataract formation. The nutrient may be beneficial because ultraviolet light and oxidative stress in the lens of your eye are thought to be leading causes of cataract formation. Vitamin C can help prevent the damage caused by oxidative stress.

Cold sufferers have raved for years about vitamin C's effect on what ails them. Research shows that high intake of this water-soluble vitamin actually supercharges some of your immune system's most important defense cells, helping them to move faster while tracking down potential pathogens such as bacteria and viruses. That means you may not be able to prevent a cold by taking vitamin C, but you can probably make it shorter and less severe. Not only that, but vitamin C has also been found to reduce the body's levels of histamine, a chemical released by the body that can dampen immune response, says Carol Johnston, Ph.D., associate professor of food and nutrition at Arizona State University in Tempe.

This antihistamine benefit may also be good news for folks suffering from asthma or allergies. Researchers at Harvard Medical School found that people who got at least 200 milligrams of vitamin C a day had a 30 percent reduced risk of bronchitis or wheezing compared with people who got about 100 milligrams of vitamin C a day.

Researchers at the Linus Pauling Institute have found that vitamin C inhibits replication of HIV, at least in infected cells in the laboratory.

One day, people with diabetes may also benefit from vitamin C. An animal study seemed to show that vitamin C helps regulate insulin release. And a human study showed that vitamin C prevents the sugar inside cells from converting to a chemical called sorbitol. This sugar alcohol, which accumulates in the cells, has been implicated in diabetes-related eye, nerve and kidney damage.

As if all of that weren't enough, vitamin C has long been known to protect gums, joints, ligaments, artery walls and skin. It also improves wound healing by aiding the production of collagen, the building block of tissues. "About one-third of your body's protein is collagen, which means you're in pretty bad shape without vitamin C," says Dr. Johnston.

Although most people have heard of vitamin C's healing benefits, many may be depleted of this important nutrient. In a study conducted at Arizona State University, Dr. Johnston found that 60 percent of the participants got about 125 milligrams of vitamin C a day, more than twice the Daily Value. Between 18 and 20 percent, however, were depleted, and roughly 3 percent had blood vitamin C levels that indicated they should be suffering from scurvy, a potentially fatal deficiency disease once common among sailors. "We saw in our population that the ones who were deficient ate less than one serving of fruits and vegetables a day, when it is recommended that you eat five to nine servings," says Dr. Johnston.

Early signs of vitamin C depletion include weakness and lethargy, followed by delayed wound healing. If stores are completely exhausted--a rare occurrence today--scurvy appears. Its symptoms include dementia, bleeding gums, tooth loss, hemorrhages and pain in muscles, bones and joints.

Using Vitamin C Safely

Scan the shelves in your local health food store, and you may see more forms and brands of vitamin C than new cars at a dealership.

But don't worry about which one to buy. At least one study shows that it doesn't seem to matter. Whether the vitamin C is top of the line or bargain basement, the amount that your body uses is the same. "I compared ones that are expensive with those that are dirt cheap--two bucks a bottle--and there was no difference," says Dr. Johnston. "In other words, additives like rose hips, manipulation like buffering and cost didn't have any impact on bioavailability." There may be one small difference, however: Buffered vitamin C could cause slightly less diarrhea in high doses than other forms.

And high doses do seem to be safe. Megadoses of vitamin C--between 500 and 2,000 milligrams every four hours--have been used to acidify urine, which affects the way some medications are absorbed. In no fewer than five clinical studies, folks who took 5,000 milligrams a day for more than three years reported no side effects. Dr. Pauling took megadoses of vitamin C every day for decades with no reported ill effects.

Doses of 500 milligrams a day have been linked to kidney stones in people who are prone to them, however. And as mentioned, large doses of vitamin C can cause diarrhea. (If you experience this reaction, experts recommend taking the vitamin in divided doses with meals throughout the day.)

Stress increases the body's need for vitamin C. So does nicotine. Because of this, the Food and Nutrition Board of the National Research Council has recommended that smokers get 100 milligrams of vitamin C per day.

The vitamin may also interfere with the absorption of tricyclic antidepressants, and it interferes with the results of certain diagnostic blood and urine tests, so you might want to mention your vitamin C intake to your doctor if you take these drugs or are going in for tests. People who have deficiencies in a red blood cell enzyme called glucose-6-phosphate dehydrogenase should not take large doses of vitamin C because it can damage their red blood cells and cause anemia. This deficiency is most common among people of African, Mediterranean or Asian descent. Some experts recommend limiting the use of chewable vitamin C tablets because they can cause enamel loss from the surface of the teeth and other dental problems.