Vitamin C: How Much Do You Really Need?
|vitamin C can prevent cancer, stop heart attacks|
Feel free to call Rusty Hoge a vitamin C zealot. He swallows a whopping 14,000 milligrams a day -- 150 times the government-set Recommended Dietary Allowance (RDA) -- and has quadrupled the dose when he felt illness coming on.
Since adopting this regimen 10 years ago, the 46-year-old telecommunications technician from suburban Atlanta claims to have been sick only once -- and then because he slacked off his normal routine. "I like to say that taking high doses of vitamin C has one side effect -- good health," he says.
Like many other devotees, Hoge believes that enormous doses of vitamin C can fend off cancer and heart disease, slow the aging process, prevent colds, and extend our lives by up to 35 years. Such claims were popularized by the late Nobel-prize winning chemist Linus Pauling, who died in 1994 at the age of 93, and his disciples continue to spread his gospel.
But hold onto your pill bottles. In recent weeks, some studies have suggested that far from being a panacea, vitamin C might actually contribute to heart disease and cancer. What's more, while Americans are now spending some $724 million per year on vitamin C pills, a government report released last April suggests that these supplements are simply unnecessary, whether in large doses or small.
So where does that leave people like Hoge . . . and the rest of us?
Good Cop or Bad Cop?
There's no question that vitamin C is vital for life, especially for
the manufacture of collagen, the rugged protein that holds your body
together. Along with vitamin E and selenium, vitamin C is also a
Antioxidants act like cops in the body, apprehending the rowdy
molecules called free radicals that form naturally during metabolism
and that can damage cells. One theory holds that free radicals
promote chronic diseases like cancer, heart disease, and
Alzheimer's, and that by increasing our consumption of antioxidants,
we can stave off these feared killers.
The studies sound alarming, but experts warn against making too much of them. While Golde says that cancer patients shouldn't take large doses of the vitamin, other researchers say it's far too early to make that recommendation. There's no evidence yet that C actually shields cancer cells from treatment, says Mark Levine, MD, an endocrinologist and Vitamin C expert at the National Institutes of Health. The cancers tested in Golde's research, he says, may simply have grown from tissues that normally take in large amounts of the vitamin.
As for the heart disease finding, Dwyer himself cautioned that it is preliminary. The study lasted only 18 months and included just 573 men. And Robert Jacob, PhD, a research chemist with the U.S. Department of Agriculture, points out that previous studies suggested just the opposite -- that vitamin C reduces the narrowing of carotid arteries.
No Magic Bullet
While the jury is still out on vitamin C's safety, a comprehensive review of the evidence suggests that taking supplements doesn't provide nearly the protection against disease that many people think it does. In a report released in April 2000, the Institute of Medicine, an independent scientific organization that advises the federal government, examined whether vitamin C and other antioxidants prevent chronic diseases. After weighing the results from more than a thousand studies, the scientists decided they didn't.
"I think what the data show is that vitamin C is an important antioxidant," says Jacob, a member of the panel. "But it's not a magic bullet. Taking more of it is not going to solve those diseases."
The Institute of Medicine panel did, however, change the recommended dietary allowance (RDA) for vitamin C. The government now advises that men get 90 milligrams per day and women 75 milligrams. Smokers should get an additional 35 milligrams a day, the panel said. That's an increase from the 60 milligrams of the previous RDA, but it's far lower than the dose in many multivitamins -- and well below the amounts that people like Hoge take.
Taking any more than about 200 milligrams per day is likely a waste of money anyway, according to a landmark study by Mark Levine of the NIH. Levine's group found that the body's cells can't absorb more than about 100 milligrams per day, and the concentration of vitamin C in the blood begins to level off at a dose of 200 milligrams per day. The study appeared in the April 1996 issue of Proceedings of the National Academy of Sciences.
The message is that large doses simply go to waste, says Balz Frei, PhD, director of the Linus Pauling Institute. "Above a certain threshold, you urinate out most of what you take in," says Frei.
The panel found no evidence of serious side effects from large doses of vitamin C, but recommended a maximum dose of 2,000 milligrams per day because of the possibility of diarrhea, an inconvenience that usually passes quickly. As a precaution, anyone with hemochromatosis, thalassemia, or a history of kidney disease should shun high doses, Jacob says. So should anyone taking blood thinners or estrogen or who has a history of renal stones. In such cases, make sure you get your doctor's advice before considering higher doses of vitamin C.
Contrary to Pauling's claims, the panel concluded that high doses of vitamin C probably won't protect you from getting a cold, either, though they may shorten the length of your suffering slightly.
Also named ascorbic acid.
As for the rest of us, scientists agree that one clear message emerges from the research: People whose diets are rich in fruits and vegetables have lower rates of cancer, heart disease, and other chronic illnesses. That means the ideal way to meet your requirements for vitamin C is by eating at least five servings of fruits and vegetables a day.