How Much Vitamin C?

A one-page study published earlier this year in Nature suggested that vitamin C pills might cause genetic damage to cells. Genetic damage can promote aging, cancer and birth defects. Such news attracted the attention of both scientists and the media. Vitamin C was blamed because vitamin C is not only an antioxidant but could be an oxidant under certain circumstances producing the free radicals that are responsible for damage to DNA, our cells' genetic codes.

Since then, many leading scientists in the field have criticized the design and methods of this small study of only 30 subjects who took 500 milligrams of vitamin C daily for six weeks. The most serious criticism is that the methods used for grinding up the cells to assay for DNA damage may have been responsible for 90 percent or more of the damage observed.

In a review of vitamin C (ascorbic acid) and disease, human as well as other kinds of studies support the important role of vitamin C in protecting health. Strong evidence points to the following benefits:

• Stomach and Other Cancers. Worldwide studies point to Vitamin C preventing stomach cancer and other gastrointestinal tract cancers of the mouth, pharynx, esophagus, and pancreas. It may also help prevent lung and cervix cancer.

• Heart Disease. Some human studies suggest that people with low levels of vitamin C are more prone to have a heart attack. Vitamin C may help prevent the oxidation of LDL-cholesterol, the "bad" cholesterol that damages and clogs arteries. It may also reduce artery constriction that limits the blood supply to the heart muscle.

• Gallbladder Disease. A recent study reported that postmenopausal women taking vitamin C supplements had less gallbladder disease than those who hadn't. Not enough vitamin C can slow down the conversion of cholesterol to bile acids, the way the liver disposes of excess cholesterol through the gallbladder. A build-up of cholesterol can lead to gall stones and gallbladder disease.

• Colds. People often treat the common cold by taking extra amounts of vitamin C. It takes some 2000 milligrams (2 grams) a day to reduce the severity and duration of a cold, but that much may cause diarrhea and kidney stones in susceptible people. Unfortunately, taking large daily doses of vitamin C does not seem to prevent colds.

• Cataracts. One usually thinks of vitamin A in connection with healthy eyes, but vitamin C may help prevent cataracts. Vitamin C supplements for over ten years can halt or prevent cataracts from developing.

How much is enough? Adult tissues can become saturated with about 200 milligrams daily. The present RDA is only 60 mg which is enough to prevent deficiency symptoms but not enough to prevent other diseases. Smokers need more because of all the free radicals that are produced when tobacco is burned. Also, researchers don't yet know how much vitamin C older people need, especially those who are chronically ill. Best guesses are that 200 milligrams is a better minimum than 60 mg but certainly a total of 250 to 500 mg daily from both foods and supplements are okay. The new RDA recommendations for vitamin C are expected in fall 1999. By the way, it doesn't matter whether or not the vitamin C is manufactured or extracted from natural sources like rose hips. Synthetic and natural vitamin have the same formula and structure.

Sources: Vitamin C under attack. University of California, Berkeley Wellness Letter. 14(10):1. July 1998. Vitamin C earns an "A" for health benefits; do you get enough? Environmental Nutrition. 21(6):1,4. June 1998.

Mary P. Clarke, Ph.D.
Extension Specialist, Nutrition Education

8/98 FILE: NUTRITION EDUCATION/General

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