Researchers Question Government Recommended Daily Allowance (RDA) for Vitamin C

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The authors of a new book claim the Institute of Medicine (IM) and the National Institutes of Health (NIH) used flawed science to develop the Recommended Daily Allowance (RDA) for vitamin C, a blunder that has likely caused millions of people to prematurely suffer avoidable health problems such as cataracts, strokes, heart attacks and many other maladies.


Steve Hickey PhD and Hillary Roberts PhD, pharmacology professors and graduates of the University of Manchester in Britain, claim they have been in communication with the NIH and the IM for over a year, challenging their rationale which establishes the RDA for vitamin C at 75 and 90 milligrams for males and females respectively. Hickey and Roberts say some basic errors in biology make justification for the current RDA for vitamin C indefensible. Even a recently proposed 200-milligram daily intake would still be inadequate to achieve optimal health says Hickey and Roberts.


The main flaw -- the half life for vitamin C is quite short, about 30 minutes in blood plasma, a fact which NIH and IM researchers have failed to recognize. (Half life is the time it takes for half of a substance to be removed from the body.) NIH researchers established the current RDA based upon tests conducted 12 hours (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."

Because vitamin C is used up rapidly, a very high single dose of vitamin C would not achieve the same concentration in the blood serum over time as two divided lower doses. Hickey and Roberts claim many negative studies using high-dose vitamin C have failed to recognize this fact and have therefore mistakenly concluded that high-dose supplemental vitamin C is ineffective.


In the past year Hickey and Roberts have shaken the confidence of the IM and NIH, revealing that the medical establishment has failed to

investigate the use of high-dose vitamin C properly, for more than 50 years. Hickey and Roberts have taken the IM and NIH to task for developing the RDA for vitamin C on studies using only 15 healthy test subjects. Normal variations would call for a greater pool of test subjects before establishment of an RDA for hundreds of millions of people.

Furthermore, the RDA is intended to set a level of nutrient consumption that would prevent disease (scurvy) among the vast majority (95%+) of the population. Yet smokers (50 million), estrogen or birth control pill users (13 million and 18 million), diabetics (16 million), pregnant females (4 million) and people taking aspirin (inestimable millions) or other drugs, have increased need for vitamin C and comprise more than 35 percent of the population. The current RDA wouldn't meet the needs of these large subpopulations.


Hickey and Roberts confronted the IM and NIH with their own contradictory data. The IM and NIH claim the saturation point is reached at a certain concentration of ascorbic acid in blood plasma but later published a paper showing repeated oral doses could achieve much higher concentrations, more than three times greater! [Annals Internal Medicine 140: 533-37, 2004].

Because of the short half-life of ascorbic acid, five 100 milligram doses of oral vitamin C taken at intervals through the day will raise average blood levels more than a single 1000 milligram dose. Hickey says the blood plasma is not saturated when 1000 milligrams of vitamin C is consumed orally since NIH researchers themselves demonstrated 2500 mg dose produces even higher concentrations. Hickey and Roberts claim the minimum supplemental dose of oral vitamin C needed to sustain blood plasma levels is around 2500 milligrams a day in divided doses in healthy individuals. Millions of others (smokers, diabetics, etc.) have needs greater than this.

NIH researchers doggedly cling to their claim that no more than 200 milligrams of oral vitamin C is required for human health and that a diet which includes five servings of fruits and vegetables would provide 210-280 milligrams of vitamin C. [Biofactors 15: 71-74, 2001]

But only 9 percent of the US population consumes 5 servings of plant foods daily. The National Cancer Institute has abandoned their 5-a-day recommendation and replaced it with 9-a-day servings of fruits and vegetables once they recognized five servings a day had not reduced the risk for cancer or heart disease.


The recommended Tolerable Upper Limit for vitamin C, 2000 mg per day, gives the false impression that amounts beyond this would be toxic or produce side effects. In fact, 2000 mg of oral vitamin C would not meet the needs of millions of American adults. The only side effect at this dose is transient diarrhea which usually dissipates over time.


The mistaken idea that high-dose vitamin C supplementation saturates the blood plasma after a moderate dose of about 150 milligrams of oral vitamin C, and additional amounts are worthless since they are excreted in the urine, now must be abandoned, says Hickey and Roberts. More than a decade ago other researchers found that consumption of high-dose vitamin C (2000 mg per day) increased ascorbic acid levels in the human eye by 22-32 percent compared to when a so-called saturation dose (148 mg) is consumed. [Current Eye Research 8: 751, 1991]

Ascorbic acid levels in other tissues in the body, such as the brain where vitamin C concentration is 10 times greater than in blood plasma [J Clinical Investigation 100: 2842, 1997] make it evident that blood plasma levels may not be the gold standard for measuring vitamin C adequacy in all tissues in the human body.


Hickey and Roberts' revealing book confirms the work of Dr. Linus Pauling, a long-time advocate of high-dose vitamin C supplementation. Pauling advocated consumption of supplemental vitamin C throughout the day and he consumed 18,000 milligrams of vitamin C in divided doses on a daily basis, a practice which overcomes the half-life decay problem.

Pauling also conducted studies using intravenous vitamin C as a treatment for cancer. In recent months published scientific reports even 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 of vitamin C that are more than six times greater than oral vitamin C. [Annals Internal Medicine 140: 533-37, 2004] Three years ago even NIH researchers proposed that ascorbate 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.


Hickey has called for the IM and NIH to retract the current RDA or provide scientific justification for their recommendation. The NIH has ceased communication with Hickey via email.

Hickey and Roberts' new book, Ascorbate: the Science of Vitamin C, is available for immediate download ($6.00) at


ISBN 1-4116-0724-4

$6.00 online download

$22.32 soft cover at
6 X 9 inch perfect bound, fully referenced, 264 pages

Hilary Roberts

Hilary has a BSc in physiology and psychology, an MSc in computer science and a PhD in child health from the University of Manchester, England. Her PhD work was on the effects of early life undernutrition on brain development and later behaviour. For a time she was a lecturer in organisational behaviour at Manchester Business School, working with Professor Enid Mumford. She was also a member of the British Computer Society's working group on Sociotechnical Systems. Hilary has scientific and other publications ranging from brain research to computer systems implementation.

Steve Hickey

Steve has a BA (maths and science) from the Open University, Membership of the Institute of Biology by examination in pharmacology, is a Chartered Biologist and a former member of the British Computer Society. In the first year of his PhD research in medical biophysics at the University of Manchester, he won the international Volvo Award for Biomechanics. In his final year, he was runner up for the Volvo Basic Science award for work on the development and aging of the spine. Other awards include the annual award and medal of the Back Pain Society (1986). Following his PhD, he worked with Professor John Brocklehust on the function of the urethra.

This was followed by research into ultra high resolution CT body scanning, leading the physics team in Europe's first clinical MR imaging unit at Manchester Medical School. He was also a member of the Medical Research Council's task force on MR imaging. Steve has over 100 scientific publications covering a variety of disciplines. Currently he is Technical Director of a computer company in Manchester Science Park. He is also working with Professor Enid Mumford on aspects of computer systems implementation.

In addition, he is a member of the Biology Department of Manchester Metropolita n University. He is currently affiliated with the Metropolitan University of Manchester.


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