Absorption of Vitamin C Megadoses

Absorption of C


Errors in statements such as "Your body cannot absorb all that vitamin C."
by Scott Roberts

Back in April 21, 1999, the Journal of the American Medical Association published an article on vitamin C that attempted to show by blood and urinary data that vitamin C in doses greater than 100 to 200 mg/day have no useful benefit in humans. The article is important because it strives to guide the new RDA for vitamin C towards a mere 100 to 200 mg/day.

The severity of the inadequacy of the article can be seen by the following observations:   The article cites a 1997 article to claim vitamin C in gram doses has no place in the treatment of colds while ignoring a Feb 1999 article by the SAME RESEARCHER that claimed 2 g/day reduces the duration of colds by 26%. The abstract of that reference is included below. Pauling claimed vitamin C would have its greatest effect on the common cold when a gram was taken every hour instead of just once a day. 

The article recommends an RDA of 100 to 200 mg/day based on arguments that are almost entirely theoretical instead of citing the many real-world studies showing substantial health benefits from levels greater than 1 g/day (including numerous studies on specific diseases done in the 1940's and 1950's - see the 1971 book by Irwin Stone "The Healing Factor: Vitamin C Against Disease," posted in its entirety at http://vitamincfoundation.org/stone/ )

By the article's own admission, it recommends an RDA of 100 to 200 mg/day based on faulty data manipulation. The authors chose to measure steady state blood plasma concentration after ingestion instead of actual concentrations because the calculation for actual concentrations was "too complex." From reading the text, one would think 60 micromol/L in the blood is as high as can be possibly achieved (which results from ingesting 100 to 200 mg/d). However, by making an estimation of their lower graph in figure 3, the data indicates that if 1,000 mg were taken 4 times a day (the minimum recommendation of several popular nutrition experts such as Dr. Whitaker, Dr. Cathcart, Dr. Hoffer, Dr. Pauling, Dr. Klenner, and Irwin Stone), it would average out to about 180 micromol/L. Surely a little more calculation (or even some estimating) would have been worth the effort to show a 3-fold increase! 

The authors' blood and urinary data used to support their suggested maximum recommended daily amount of 100 to 200 mg/d is claimed to be better than data previously available. The JAMA article's data and arguments are 20 years old. Linus Pauling in his 1986 book "How to Live Longer and Feel Better" used nearly the exact same blood, urine, and absorption data (p 108-112) to address the exact same misunderstandings to show that 140 mg/d should be considered an absolute minimum value instead of a maximum. Pauling believed the optimum range of vitamin C for most people would be between 3 and 20 g/d. 

The authors do not seemed bothered or amazed that their claims indicate humans need 10 to 100 times less vitamin C than almost every other animal on the planet (adjusted for body-weight). Gorillas get 20 to 40 times as much in their diet and the RDA-equivalent for monkeys is also about 20 to 40 times higher than the authors are recommending for humans. Why is the RDA set so low for humans and so high for monkeys? 

The authors do not give any physiological explanation for why they believe humans are so unique among the animal kingdom as to find relatively small doses (1 g/d) of vitamin C "toxic." This size dose has never resulted in a human suffering an adverse health effect (other than those who are sensitive to it have temporary diarrhea). The article discusses increased iron absorption and oxalate production, but no case of a human being harmed is reported. The article's suggested "toxic" level for humans is approximately the bare minimum needed by all other animals. Other large mammals sacrifice 2% to 4% of their daily food energy to make vitamin C in concentrations 10 to 20 times higher than what the article considers "toxic," showing that not only is it not toxic, but it's more important than having a little extra food! 

Here is a study to consider: "Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit." Hemila H. Department of Public Health, University of Helsinki, Finland.  Med Hypotheses 1999 Feb;52(2):171-8:

ABSTRACT: Placebo-controlled trials have shown that vitamin C supplementation decreases the duration and severity of common cold infections. However, the magnitude of the benefit has substantially varied, hampering conclusions about the clinical significance of the vitamin. In this paper, 23 studies with regular vitamin C supplementation (> or = 1 g/day) were analyzed to find out factors that may explain some part of the variation in the results. It was found that on average, vitamin C produces greater benefit for children than for adults. The dose may also affect the magnitude of the benefit, there being on average greater benefit from > or = 2 g/day compared to 1 g/day of the vitamin. In five studies with adults administered 1g/day of vitamin C, the median decrease in cold duration was only 6%, whereas in two studies with children administered 2 g/day the median decrease was four times higher, 26%. The trials analyzed in this work used regular vitamin C supplementation, but it is conceivable that therapeutic supplementation starting early at the onset of the cold episode could produce comparable benefits. Since few trials have examined the effects of therapeutic supplementation and their results have been variable, further therapeutic trials are required to examine the role of vitamin C in the treatment of colds.

Some writers have claimed that excess vitamin C is excreted immediately.  Taking 5 hours for blood concentration of vitamin C to drop to levels that are still 2 times higher than normal steady state levels is not what I'd call "immediate" excretion.   At two hours after the dose, vitamin C concentration is almost 4 times steady state levels. This data is for 1250 mg.  For the proof of my statements, see figure 3 in the reference and paragraph 2 of page 1418 in the PDF file.

If someone is taking large doses of vitamin C they should not just stop. The body has altered its absorption rate and it takes a while for it to readjust. One should taper off of large doses gradually. Linus Pauling believed in the "rebound scurvy" effect. He said you'd be more susceptible to colds if you skipped even a day (if you took the large doses). Interestingly, the JAMA article says it is a myth. 

Personal viewpoint: 
Some vitamin C critics' personalities remind me a little of me before i starting taking normal Earth animal size doses of ascorbic acid powder (16 grams/day in 4 glasses of grape or orange juice spaced apart). My yearly physicals don't show any change in metals. Cholesterol from 210 to 160. Stress level plummeted. I still get a cold once a year, but my nose never gets stuffy.  I used to always have to have facial tissue boxes in places like my car, desk drawer, den, and bedroom, but now I never need them.

There is also a surprising "high" I get. I can't compare it to anything - it just makes me feel better. It lasts at least an hour and often up to 2 hours, right in-line with figure 3 in the JAMA article. It's probably above 400 micromol/L in plasma that causes the high feeling (in me, not necessarily others). It's sort of like pressure in my head is reduced. I feel like the relief in stress relaxes me. The high feeling is stronger when it's been awhile since the last dose. I take the large doses because it makes me feel better, not because it's good for my health. I'll notice I'm not feeling good and say "Hmmmm, 4 grams sure would hit the spot right now." Even if I don't have juice available, I'll put the powder ascorbic acid in water and bear the bitterness. By the way, it is less acidic than cola soft drinks, even at 10 grams C per glass of water.

Edited and reprinted with the permission of Scott Roberts, December 2, 1999.
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Revised and updated 2023 by Andrew W. Saul.

Additional Comment by Andrew W. Saul: 

 The internet, discount stores and even health food stores have deals on vitamin C. My son and my daughter (vitamin C megadosers since infancy; all the way into college and not one dose of any antibiotic... I'll put the wallet full of pictures away now; pardon me) found vitamin C at a chain store for just over two cents a gram, in tablets.  Is that ever cheaper than the new, costly and side-effect-ridden antibiotics so quickly prescribed by so many physicians! During illness, even more frequent doses are indicated (sources are below for those interested.)  "C" every ten minutes is not at all too often during the 'flu.

Mr. Roberts' experience with vitamin C so closely parallels my own that I'll just conclude with a "right on."

Dr. Frederick R. Klenner's Clinical Guide to the Use of Vitamin C is now posted in its entirety at


The complete text of Irwin Stone's book The Healing Factor: Vitamin C Against Disease  is now posted for free reading at



Andrew W. Saul


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