CORVALLIS, Ore. - The recommended dietary allowance, or RDA, for vitamin C should be officially doubled to a new level of 120 milligrams per day, researchers conclude in a new report, with potential benefits for everything from heart disease to cataracts and cancer.
The study, published in the American Journal of Clinical Nutrition by scientists from the Linus Pauling Institute at Oregon State University, says the time is past when the amount of vitamin C that can prevent the 16th century sailor's disease of scurvy is considered all that's needed for optimal health.
The current recommendation of 60 milligrams of vitamin C daily has been in place for decades and is reflected in medical textbooks, many vitamin supplements and nutritional folklore. But it doesn't reflect the wealth of new research done in recent years, which shows that slightly higher levels of this antioxidant vitamin could play a more important role in prevention of degenerative disease.
"If the antioxidant function of vitamin C is accepted as relevant to and important for human health, then morbidity and mortality from cancer, cardiovascular disease and cataract - in addition to scurvy - must be used as criteria for determining vitamin C requirements," said Balz Frei, professor and director of OSU's Linus Pauling Institute.
The totality of evidence from human studies strongly suggests a dietary intake of at least 90-100 milligrams of vitamin C is associated with reduced risk of cardiovascular disease and cancer, and even higher intakes to reduce cataract risk, said Frei and research associate Anitra Carr in the new report.
Although many people take supplements of up to 2,000 milligrams per day or even more with no apparent ill effects, studies show that in healthy people tissue saturation of vitamin C usually occurs with intakes of about 100 milligrams per day. And some studies have found little to be gained on at least some medical conditions with intake levels a great deal higher than that.
The OSU researchers said they therefore recommend - with solid scientific data to support - an official doubling of the RDA to 120 milligrams per day.
"We most strongly support an intake of five to nine servings of fruits and vegetables a day, which provides more than 200 milligrams of vitamin C," Frei said. "Unfortunately, only a small minority follows these guidelines, and doctors often do not make a strong point about them either because they are trained to treat disease, not prevent it. Lacking a proper diet, the next best thing is a multivitamin."
To take care of all antioxidant needs, Frei said he personally recommends the "200 rule."
This includes 200 milligrams a day of vitamin C, preferably from fruits and vegetables; 200 international units of natural source vitamin E as a supplement; and 200 micrograms of selenium, about half of which is provided by a healthy diet with fruits and vegetables, and the other half should come from a supplement. Frei does not recommend beta carotene supplements.
Vitamin C has long been known as an essential micronutrient required for normal metabolic functioning of the body. A chronic deficiency of it can cause the debilitating disease of scurvy, a condition that plagued early sailors on long voyages until they learned to carry along citrus fruits to suck on - and British sailors became known as "limeys." But modern medicine embraced the amounts of vitamin C that were ample to prevent scurvy and death as essentially adequate for all other purposes.
That assessment, Frei said, has fallen by the wayside as study after study sheds new light on the role that antioxidants can play in degenerative disease, aging, cognitive and immune function and overall health. And for various biochemical reasons, vitamin C is still the king of antioxidants.
Antioxidants readily scavenge many reactive oxygen and nitrogen species such as superoxide and hydroperoxyl radicals, hydroxyl radicals, peroxynitrite, nitrogen dioxide, and hypochlorous acid.
Antioxidants protect from oxidative damage such "substrates" as proteins, lipids, carbohydrates and DNA. And oxidative damage has been implicated in cancer, cataracts and cardiovascular disease - the leading cause of death in the United States, which last year alone caused almost a million deaths and an estimated $286 billion in health care expenditures and lost productivity. Nutritional deficiencies are also a special concern for smokers, pregnant or lactating women, and the elderly.
A diet rich in fruits and vegetables will probably provide ample vitamin C and other antioxidants, the OSU researchers said, along with other fiber, phytochemicals and micronutrients. For that reason, a good diet is still the preferred way to obtain all micronutrients. But in the real world of fast food where people think of french fries and ketchup as vegetables, they said, that type of diet is rare.
In the United States, about 25 percent of men and women consume less than the current RDA of 60 milligrams per day of vitamin C, and 10 percent of adults consume less than 30 milligrams. Vitamin C levels are usually lower in smokers, most likely as a result of oxidative stress. And although oxidative processes have been implicated in aging and cognitive processes, the elderly are often prone to vitamin C deficiency as a result of poor dietary habits or increased needs.
"The potential of adequate vitamin C and other micronutrients to benefit public health and reduce the economic and medical costs associated with chronic diseases is enormous," the OSU researchers concluded in their report.
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