C is for Controversy

How much vitamin C do we need?

Vitamin C is a celebrity among vitamins. It is necessary for human life, and many people endow it with almost magical powers. The most casual search of the Internet or your local library will tell you that claims and controversy about vitamin C are never ending.

Some facts are not in dispute: Vitamin C prevents and cures scurvy, a disease that, because of improvements in diet worldwide, is hardly seen anymore. It is a powerful antioxidant, meaning that it neutralizes potentially harmful free radicals in our bodies. (However, it may also, under some conditions, become a pro-oxidant, meaning it can promote the production of free radicals.)

It is essential for healthy skin and connective tissue, and for the absorption of iron, as well as other functions. It is water-soluble, and the body can store only small amounts; excess C is eliminated by the kidneys. Thus, humans must consume vitamin C on a regular basis. Many fruits and vegetables are rich in it, especially citrus fruits, peppers, broccoli, strawberries and cantaloupe. Meats and fish have none. Cooking and processing reduce vitamin C.

A Big Dispute: How Much Do We Need?

Current government guidelines call for 75 milligrams daily for women and 90 milligrams for men--the amount in about six ounces of orange juice. Smokers need an extra 35 milligrams a day, as do those exposed to tobacco smoke. The safe upper limit is 2,000 milligrams. Higher doses are not toxic, but may cause diarrhea.

But no matter how modest government guidelines remain, many people believe that vitamin C will prevent or cure almost every disease. Linus Pauling was a brilliant American chemist whose research helped reveal the structure of DNA and who won two Nobel prizes (one in chemistry in 1954, plus one for peace in 1962 for his campaign against nuclear weapons). He became the great champion of vitamin C, believing, in effect, that humans must suffer from a general kind of vitamin C deficiency disease, and that big doses would work magic for them. He and his colleagues insisted that megadoses of C (3,000 milligrams or more a day) would prevent or cure the common cold and cancer, among other ills. But scientific experiments repeatedly failed to back up these theories, and Pauling gradually lost the support of the scientific community.

From 1932 until now, no vitamin has been the subject of more research. Indeed, vitamin C has spawned an industry. Thousands of studies of C have been done, at a cost of millions or billions of dollars. And yet, in a way, we have learned very little, at least if we expected miracle cures. The wisdom of consuming foods that contain C is incontestable. But small amounts of the vitamin seem to work as well as larger amounts, and no one has shown that supplements are beneficial.

Findings About Vitamin C

  • According to an extensive review of studies by the Cochrane Collaboration (an independent organization that evaluates medical research) in 2004, vitamin C supplements do not prevent colds. There was some evidence they might reduce the incidence of colds under extreme conditions, such as in the Arctic, but this is no help to people under ordinary conditions.

  • According to the Natural Standard (a group of scientists that reviews findings in alternative medicine), there is no clear evidence that vitamin C prevents or cures cancer, cataracts or heart disease.

  • A recent analysis of studies on antioxidant supplements in the Journal of the American Medical Association concluded that vitamin C pills do not help people live longer.

  • In 2005 Italian researchers found that high blood levels of vitamin C were linked with cataracts--contrary to expectations. Another study failed to find that antioxidants, including C, slowed the progression of cataracts.

  • Many studies have shown that smokers and people exposed to secondhand smoke have lower blood levels of vitamin C and that they need to consume more C--hence the government recommendation that smokers need extra C. Of course, quitting smoking and avoiding smoke would benefit them more.

  • Studies of vitamin C as a possible cancer treatment are underway, but so far the news has not been encouraging. There is also some concern that high doses of C may actually harm cancer patients--for example, by interfering with chemotherapy.

Bottom Line

In spite of the thousands of studies conducted since the 1930s, the only certainty is that vitamin C prevents scurvy and plays other basic roles in human health. An intake of 75 to 90 milligrams daily appears to be all you really need. More does not seem to be better, except in the case of smokers--and then only an extra 35 milligrams is needed.

If, however, you eat nine servings of fruits and vegetables daily, as we recommend, you'll get far more C--probably 200 to 500 milligrams a day. There's no evidence you need this much, but such a diet will also supply many other nutrients that, all together, will help keep you healthy and may reduce your risk of cancer and heart disease. In other words, in striving to consume more C, you'll improve your diet. Supplementation is not necessary or recommended.  


Reprinted, courtesy of University of California Berkeley. For more articles and information, visit www.wellnessletter.com .

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