Recent headlines announcing that moderately high doses of vitamin C — 500 milligrams?might be dangerous stunned the many Americans who routinely take high-dose C supplements. The British study behind the headlines has since come under attack by researchers who believe it was seriously flawed. Whether it is necessary to take that much vitamin C is another question altogether. What isn’t disputed is the plethora of scientific evidence upholding C’s claim to nutritional stardom.
Vitamin C and Cancer. Studies from around the world have consistently reported links between diets high in vitamin C and reduced risk of several kinds of cancer, mostly of the gastrointestinal tract, including the mouth, pharynx, esophagus, stomach and pancreas, but also the lung and cervix.
The most evidence, however, is for the prevention of stomach cancer. An international panel of experts concluded late last year that getting more than the currently recommended intake of vitamin C may help prevent this disease. (See EN, March 1998.) A recent animal study suggests one reason why: High doses of vitamin C inhibit H. pylori, the bacterium that causes most ulcers and may be responsible for an increased risk of stomach cancer.
Vitamin C may help prevent cancer in other ways as well, perhaps by neutralizing free radicals or blocking the formation of nitrosamines. These are carcinogenic compounds that form when nitrates (found naturally in foods and as food additives) or nitrites (found naturally in saliva) combine with substances called amines in the stomach’s digestive juices.
Vitamin C and Heart Disease. There is also evidence that vitamin C may help keep arteries healthy. A study of Finnish men, for example, found that those who were deficient in vitamin C had a much greater risk of heart attack than those who weren’t. Yet this shows only that a vitamin C deficiency is harmful, not that extra C is protective.
Still, studies comparing people from different countries show less risk of cardiovascular diseases for those who eat more of foods rich in antioxidant nutrients like vitamin C. And, this link fits nicely with one current theory of atherosclerosis (hardening of the arteries). Researchers now believe cholesterol starts clogging heart vessels only after low-density lipoproteins (LDL’s, the “bad” cholesterol) become oxidized. It follows that antioxidants, including vitamin C, could prevent the oxidation of LDL’s and thus prevent atherosclerosis. Yet some researchers believe vitamin C helps the heart in other ways as well.
“Vitamin C probably does more than just inhibit LDL oxidation,” surmises Balz Frei, Ph.D., director of the Linus Pauling Institute at Oregon State University. “These effects may be just as important?or perhaps even more important’than its role in inhibiting LDL oxidation.” Frei explains that when blood vessels constrict, they cut off the blood supply to the heart, and a number of studies show vitamin C can prevent this from happening, even in people who already have cardiovascular disease or high levels of LDL-cholesterol.
Some researchers believe one of vitamin C’s most important roles may be to make vitamin E a more effective antioxidant, in essence regenerating E so it can snare more free radicals. “However,” cautions Frei, “so far this has only been shown in the test tube.”
Vitamin C and Gallbladder Disease. What do gallstones and heart attacks have in common? Cholesterol. Bile, the digestive substance stored in the gallbladder, is made from cholesterol. One of the ways the body gets rid of cholesterol is to convert it to bile acids.
“But when blood levels of vitamin C are low, the body’s conversion of cholesterol to bile acids slows down. As cholesterol builds up in bile, gallstones may form,” says Joel Simon, M.D., of the University of California at San Francisco. In a recent study, Simon found a marked reduction in gallbladder disease among postmenopausal women taking vitamin C supplements.
Vitamin C and Cataracts. Although vitamin A is the nutrient usually associated with healthy eyes, it’s vitamin C that may counteract cataracts. A number of studies have found that regular, long-term use of vitamin C supplements can greatly reduce the risk of cataracts. Researchers at Tufts University and Harvard University studied nearly 250 women with no history of cataracts and found that those who took vitamin C supplements for at least 10 years had 77% fewer early-stage opacities (the first sign of cataracts) and 83% fewer moderate opacities than those who didn’t take supplements. How much C is needed? Researchers can’t seem to agree, but 150 to 250 milligrams is the amount that saturates eye tissues.
Vitamin C and Colds. Though certainly nor a serious malady, the common cold affects us all, and is the condition that comes to mind when talking vitamin C and disease prevention. But if you took lots of extra vitamin C last winter in hopes of preventing a cold, your money might have been better spent on extra tissues. Research shows high doses of vitamin C can’t prevent you from catching a cold, though several studies have found that extremely large doses (about 2,000 milligrams a day) can reduce the severity and duration of a cold’s symptoms slightly. That much, however, might also cause diarrhea and kidney stones in susceptible people.
To Supplement or Not? The current Recommended Dietary Allowance (RDA) for vitamin C for adults is 60 milligrams a day (100 milligrams for smokers). This amount is calculated to be sufficient to prevent scurvy’the vitamin C deficiency disease?plus a generous safety factor. But some experts argue the RDA should reflect the additional health benefits of higher intakes. A revised RDA for vitamin C is expected in the fall of 1999.
“For healthy people, my best recommendation at this time is to get at least 200 milligrams of vitamin C a day,” says Pauling Institute’s Frei. “Research has shown this is the amount that [results in] maximum levels in the body’s tissues.” A 1996 National Institutes of Health study came to this same conclusion. Moreover, it found that daily intakes above 400 milligrams had no apparent value.
Frei admits researchers really don’t know yet how much vitamin C is needed for older people, smokers or those with health problems to reach the same level of saturation in the body. For now, however, 200 milligrams seems a reasonable level for everyone to shoot for.
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