The recommended dietary allowance (RDA) of vitamin C is less than half what it should be, scientists stated in a recent report. They argue that is because medical experts insist on evaluating this nutrient in the same way they do pharmaceutical drugs and, as a result, reach faulty conclusions.
The researchers, in Critical Reviews in Food Science and Nutrition, say there's compelling evidence that the RDA of vitamin C should be raised to 200 milligrams per day for adults, up from its current levels in North America of 75 milligrams for women and 90 for men.
Rather than just prevent the vitamin C deficiency disease of scurvy, they say, it's appropriate to seek optimum levels that will saturate cells and tissues, pose no risk, and may have significant effects on public health at almost no expense -- about a penny a day if taken as a dietary supplement.
"Significant numbers of people in the U.S. and around the world are deficient in vitamin C, and there's growing evidence that more of this vitamin could help prevent chronic disease," the scientists said. "The way clinical researchers study micronutrients right now, with the same type of so-called 'phase three randomized placebo-controlled trials' used to test pharmaceutical drugs, almost ensures they will find no beneficial effect. We need to get past that."
Unlike testing the safety or function of a prescription drug, the researchers said, such trials are ill suited to demonstrate the disease prevention capabilities of substances that are already present in the human body and required for normal metabolism. Some benefits of micronutrients in lowering chronic disease risk also show up only after many years or even decades of optimal consumption of vitamin C -- a factor often not captured in shorter-term clinical studies.
A wider body of metabolic, pharmacokinetic, laboratory and demographic studies suggests just the opposite, that higher levels of vitamin C could help reduce the chronic diseases including heart disease, stroke, cancer, and the risk factors that lead to them, such as high blood pressure, chronic inflammation, poor immune response and atherosclerosis.
"We believe solid research shows the RDA should be increased," they said. "And the benefit-to-risk ratio is very high. A 200 milligram intake of vitamin C on a daily basis poses absolutely no risk, but there is strong evidence it would provide multiple, substantial health benefits."
An excellent diet with the recommended five to nine daily servings of fruits and raw or steam-cooked vegetables, together with a six-ounce glass of orange juice, could provide 200 milligrams of vitamin C a day. But most North Americans do not have an excellent diet.
Even at the current low RDAs, various studies in the U.S. and Canada have found that about a quarter to a third of people are marginally deficient in vitamin C, and up to 20 percent in some populations are severely deficient -- including college students, who often have less-than-perfect diets. Smokers and older adults are also at significant risk.
Even marginal deficiency can lead to malaise, fatigue, and lethargy, researchers note. Healthier levels of vitamin C can enhance immune function, reduce inflammatory conditions such as atherosclerosis, and significantly lower blood pressure.
The scientists noted in this report that some health benefits correlate even more strongly to vitamin C plasma levels than to fruit and vegetable consumption, suggesting that vitamin C is responsible rather than another component in fruit and vegetables.
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