Is the Recommended Dietary Allowance for Vitamin C Too Low?
by Bill Sardi by Bill Sardi
Got a bottle of vitamin C somewhere in the kitchen cupboard? Most Americans do. A quick examination of the label on the back of the bottle reveals 60 milligrams provides 100 percent of the Recommended Dietary Allowance. That’s far from what Dr. Linus Pauling suggested to achieve optimal human health. Dr. Pauling consumed 18,000 milligrams per day, claiming this water-soluble vitamin needed frequent replenishment through the day to achieve optimal health. Now freshly published research confirms many of Dr. Pauling’s suggestions, but not without plenty of controversy.
Vitamin C advocates on the defensive
Considerable disagreement has ensued in the past decade over how much vitamin C should be consumed by adults. Vitamin C advocates have continually been on the defensive.
The most recent negative news story about vitamin C emanated from Duke University where researchers mistakenly concluded from an animal study that more than the Recommended Dietary Allowance for vitamin C may worsen joint problems. But an earlier large-scale human study showed that adults who consume high-dose vitamin C experience a 3-fold reduction in the risk for progression of their knee osteoarthritis and that supplemental vitamin C reduces knee pain. [Arthritis Rheumatism 39:648—56, 1996] How did an animal study receive so much publicity when a contrary human study had already been published?
Then back in 2001 a paper in Science Magazine errantly claimed that high-dose vitamin C might damage DNA. Again, the recommendation was issued to limit supplemental vitamin C to no more than the RDA. However, this recommendation was again based a test-tube study. Five human studies had already been conducted proving high-dose vitamin C does not damage DNA, but were overlooked by the reviewers at Science Magazine. When I called this to their attention they printed my rebuttal letter which cast doubt on the test-tube study which errantly warned the public away from high-dose vitamin C supplements.
Vitamin C advocates go on the offensive
Now, however, vitamin C advocates are about to go on the offensive. In their new book, Ascorbate: The Science of Vitamin C (www.lulu.com), Professors Steve Hickey and Hilary Roberts at the University of Manchester in Great Britain allege the RDA for vitamin C has mistakenly been set too low. For the past year the British professors have been taking researchers at the Institutes of Medicine (IM) and the National Institutes of Health (NIH) to task for faulty science. Drs. Hickey and Roberts claim researchers established the current RDA for vitamin C without recognition of its half-life. In about 30 minutes, half of any dose of vitamin C disappears from the human body. The RDA was established by measuring blood plasma levels of vitamin C 12 hours, or 24 half-lives, after consumption. “To be blunt,” says Hickey, “the NIH gave a dose of vitamin C, waited until it had been excreted, and then measured blood levels.”
Furthermore, the IM and NIH developed the current RDA using studies of just 15 subjects, not nearly enough to statistically establish an RDA for a population of 280 million people.
Hickey and Roberts claim the amount of vitamin C needed for optimal health is likely to be more like 2500 milligrams per day, nearly 42 times greater than the current 60 milligram RDA.
Recent studies authored by NIH researchers confirm that the saturation point for vitamin C in blood plasma is not fully achieved even when taking doses as large as 2000 milligrams per day. Some of these studies now even confirm Dr. Pauling’s claims that high-dose vitamin C may be effective against cancer.
In recent months published scientific reports call for a reevaluation of the use of high-dose intravenous vitamin C for cancer treatment now that a study shows that intravenous vitamin C can produce blood plasma concentrations that are more than six times greater than oral vitamin C. [Annals Internal Medicine 140: 533-37, 2004] Three years ago even NIH researchers themselves proposed that vitamin C treatment of cancer should be reexamined by rigorous scientific scrutiny in the light of new evidence. [J Am College Nutrition 19:423—5, 2000]
The inability to improve survival times in cancer patients with conventional cancer treatment has been disheartening. In 1991, it was reported that supplemental vitamin C, received by incurable cancer patients at some time during their illness, more than doubled their survival time. [Medical Hypotheses 36: 185—89, 1991] Indeed, Pauling and associates demonstrated that high-dose vitamin C more than quadrupled the survival times of terminal cancer patients. [Proceedings Nat’l Academy Sciences 73: 3685—89, 1976] But Pauling’s research was discredited later when scientists claimed as little as 150 milligrams of vitamin C saturates the blood plasma and any more vitamin C than that is excreted. Now researchers recognize they made a grave error. Pauling even demonstrated that mice given high doses of vitamin C in their food were five times less likely to develop skin tumors when exposed to ultraviolet radiation than mice on low vitamin C diets. [Am J Clinical Nutrition 54:1252S—1255S, 1991] The significance here is that even high-dose oral supplementation may have preventive effects against certain forms of cancer.