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In the 1960s and 1970s, an American theory advocating the benefits of mega doses of vitamin C developed and became firmly established in people's minds and practices.
This is all the more so since its main promoter, Professor Pauling, had won two Nobel Prizes for his previous work.
Mega-doses of vitamin C were not only supposed to eliminate colds and other common illnesses, but also to reduce the incidence of cancer and significantly extend lifespan.
None of these intuitions have been scientifically confirmed, but commercial interests, particularly in the USA where this theory has caused sales of vitamin C to explode, have for many years been able to minimize the contradictions that are harmful to business.
We summarize the essentials in the following lines.
A peculiarity of vitamin C: humans cannot synthesize it
After the discovery and isolation of ascorbic acid, vitamin C was the subject of numerous studies.
Those of Professor Lehninger in 1957 showed that humans and some other mammals* cannot produce vitamin C, unlike most animals.
As a result of an ancestral genetic mutation, their cells lack a key enzyme for the biosynthesis of ascorbic acid.
Therefore, ascorbic acid is a vitamin for humans. It is a micronutrient that must be provided through food.
At that time, the question of the appropriate dose remained unanswered. It was known that very small amounts (10 mg per day) were sufficient to prevent and even cure scurvy , but optimal intakes had not yet been defined.
*(mainly primates: gorillas etc., but also guinea pigs and bats)
Mega-doses of vitamin C: a theory under commercial influence?
At the end of the 1960s in the USA, the converging visions of two men gave rise to a theory in favor of Mega-doses of vitamin C.
The first was Professor Linus Pauling, a two-time Nobel Prize winner in medicine, and the second was Irwin Stone, a biochemist working in a laboratory producing ascorbic acid who was well aware of its antioxidant properties for use as a food additive.
In 1970, Pauling published the book "Vitamin C and the Common Cold," recommending doses of at least 3 grams per day. He himself did not hesitate to consume up to 18 grams per day in the hope of longevity.
The result of this publication was spectacular in terms of vitamin C sales in the USA, which increased tenfold in just a few months!
Pauling and Stone didn't stop at the common cold. They gradually expanded the scope of the benefits of Mega-doses of vitamin C to include cancer, longevity, retinal detachment, and even AIDS, which was beginning to take its toll.
And even if scientific demonstrations were lacking, the credibility of Professor Pauling and the hopes raised by thesemiraculous benefits were creating new followers every day...And sales of Vitamin C were still increasing!
Professor Linus Pauling died of prostate cancer in 1994, without the mega-doses of vitamin C he had been taking for years being able to stop it.
The measured but limited effectiveness of vitamin C against the common cold
Vitamin C consumption is often associated with winter illnesses.
It was long thought that heavy consumption could reduce symptoms more quickly.
However, in 2013, two researchers published a synthesis [1] which concluded:
"Regular vitamin C intake had no effect on the incidence of the common cold in the general population, based on 29 comparisons of trials involving 11,306 participants. However, regular supplementation had a modest but consistent effect on reducing the duration of cold symptoms, based on 31 comparisons of studies involving 9,745 cold episodes."
This reduction in average duration is around 10%. This corresponds in practice to a cold lasting 10 days instead of 11.
Mega-doses of vitamin C and cancer?
Other research has obviously focused on the impact of vitamin C supplements on reducing cancer risks.
But clinical trial results show that vitamin C supplements (usually taken with other nutrients such as vitamin E and zinc) have no observed effect.
Similar conclusions were reached when studying possible links between vitamin C and pneumonia.
Dr. John Erdman, a member of the US Vitamin A Requirement Committee, concluded: " Many people have tried to give high levels of a single nutrient like vitamin C and study everything from cardiovascular disease to cancer to cataracts, and most of these trials have been very disappointing ."
Today, the theory of the usefulness of mega-doses of vitamin C for cancer prevention is no longer a reference.
On the other hand, among the positive effects noted, at reasonable dosages we can mention:
- Ongoing evaluations for post-chemotherapy recovery (including Dr. Moynihan's studies).
- Improved blood microcirculation in smokers.
- The antioxidant and anti-free radical properties of vitamin C to limit degenerative mechanisms.
Mega doses of vitamin C are not absorbed!
We now know that high single doses of vitamin C are useless.
The intestinal absorption process* of vitamin C is an active mechanism, requiring energy and dependent on the availability of sodium. It is a saturable mechanism that limits the absorption capacity of vitamin C into the blood.
The higher the dose, the less it is absorbed! The excess not absorbed in the intestine is directly eliminated in the stool.
At doses of 100 mg and below, intestinal absorption is good and greater than 80%. It drops to less than 20% for doses of 1000 mg. This natural absorption limit demonstrates the uselessness of high unit doses (more than 200 mg).
This is also confirmed by measurements of vitamin C concentration in the blood.
Maximum plasma concentrations of around 70 µmol of vitamin C/litre are achieved with regular intakes of 60 mg/day. Higher intakes do not significantly increase this level.
Higher doses may be useful occasionally to correct a very low level, but the excess blood will be quickly eliminated through the urine.
The ideal remains moderate but daily intake of vitamin C!
* part of the vitamin C can be absorbed at the buccal/sublingual level: case of lozenges or sprays.
Side effects of high doses of vitamin C
There are risks of side effects with massive doses of vitamin C.
Ascorbic acid is highly soluble in water. This explains why excess amounts are easily eliminated in the urine and the virtual absence of negative effects from overdoses.
This is also the reason why the European authorities (EFSA) have not clearly decided on a DJM (Maximum Daily Intake) for vitamin C.
However, certain negative effects associated with regularly taking high doses require further investigation:
- The reversal of oxidative properties: at moderate doses, vitamin C is an antioxidant and very useful for the blood fixation of iron. At high doses, it generates highly oxidizing peroxide and ascorbate radicals. This may explain observations of reduced resistance to effort in athletes who have taken doses of 1000 mg of vitamin C [9] .
- Higher incidence of cataracts?
- Kidney damage in susceptible individuals: Excess ascorbic acid is broken down into oxalate before being eliminated in the urine via the kidneys. High doses of vitamin C induce large amounts of oxalate, which can accumulate in the kidneys and cause nephropathy (kidney stones).
Therefore, it is not recommended to exceed a dose of 2 grams per day.
What is the ideal dosage for vitamin C?
The benefits of vitamin C are numerous:
- Anti-aging : by stimulating collagen synthesis and the anti-oxidant effect,
- On blood microcirculation,
- On the production of bodily energy,
- On tone and the immune system ,
These benefits are achieved with moderate daily doses of 60 to 120 mg.
Mega-doses of vitamin C are not used by the body and the hopes raised by scientific intuitions from the 1970s have never been confirmed since.
Bibliography:
- https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD000980.pub4/full “ Vitamin C for preventing and treating the common cold"
- Aghdassi E, Royall D, Allard JP (1999). Oxidative stress in smokers supplemented with vitamin C. Int J Vit Nutr Res 69: 45-51.
- Cook JD, Watson SS, Simpson KM, Lipschitz DA, Skikne BS (1984). The effect of high ascorbic acid supplementation on body iron stores.
- Curhan GC, Willett WC, Speizer FE, Stampfer MJ (1999). Intakes of vitamins B6 and C and the risk of kidney stones in women. Am Soc Nephrol 10:840-845.
- Valéry Rasplus (ed.), Sciences and Pseudo-Sciences. Views of the Human Sciences, Paris, Éditions Matériologiques, coll. “Sciences and Philosophy”, 2014, 178 p.
- https://pubmed.ncbi.nlm.nih.gov/18210337/ Comparative Study “Concentrations of vitamin C, vitamin B12 and folic acid in patients treated with hemodialysis and on-line hemodiafiltration or hemofiltration ”
- https://pubmed.ncbi.nlm.nih.gov/10527771/ “A single high dose of vitamin C counteracts the acute negative effect on microcirculation induced by smoking a cigarette” J Zhang , X Ying
- Vitamin C blood test - High Authority of Health 2018
- https://pubmed.ncbi.nlm.nih.gov/37417662/ “Vitamin C Supplementation and Athletic Performance: A Review (2023)” Dylan R Rogers , Denis J Lawlor, James L Moeller
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10017928/ “Megadose Vitamin C Prescription Through Alternative Medicine Leading to End-Stage Renal Disease: Case Study and Literature Review (2023)
