Talk:Vitamin C

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 Definition Required by a few mammalian species, including humans and higher primates. It is water-soluble and is usually obtained by eating fruits and vegetables; associated with scurvy (hence its chemical name, ascorbic acid). [d] [e]

Contents

Removed during Big Cleanup

Image:Ascorbic_acid.png|right|frame|Chemical structure of vitamin C

Image:Ascorbic-acid-3D-vdW.png|thumb|right|200px|Model of the vitamin C (L-ascorbic acid) molecule. Black is carbon, red is Oxygen and white is Hydrogen

Image:GyorgyiNIH.jpg|thumb|200px|right|Albert Szent-Györgyi, pictured here in 1948, was awarded the 1937 Nobel Prize in Medicine for the discovery of vitamin C

Image:Rosa canina hips.jpg|right|thumb|Rose hips are a particularly rich source of vitamin C

Image:Goat.jpg|thumb|250px|Goats, like almost all animals, make their own vitamin C. An adult goat will manufacture more than 13,000 mg of vitamin C per day in normal health and as much as 100,000 mg daily when faced with life-threatening disease, trauma or stress.

Image:RedoxonVitaminC.jpg|thumb||right|Vitamin C is widely available in the form of tablets and powders. The Redoxon brand, produced by Hoffmann-La Roche was the first mass-produce synthetic vitamin C and was launched in 1934.

Pierre-Alain Gouanvic 00:05, 20 November 2007 (CST)Image:Ambersweet oranges.jpg|right|thumb|Citrus fruits were one of the first sources of vitamin C available to ship's surgeons. Pierre-Alain Gouanvic 04:38, 21 November 2007 (CST) Image:James lind.jpg|180px|right|thumb|James Lind (1716 – 1794), a British Royal Navy surgeon who, in 1774, identified that a quality in fruit prevented the disease of scurvy in what was the first recorded controlled experiment.


Image:Pauling Vit C Book Cover.jpg|right|thumb|250px|Linus Pauling's popular and influential book How to Live Longer and Feel Better, first published in 1986, advocated very high doses of vitamin C.

Serum and plasma vitamin C measurements do not correlate well with tissue levels while lymphocyte vitamin C levels provide the most accurate assessment of the true status of vitamin C stores and are not affected acutely by circadian rhythm or dietary changes.”


Template:Pauling

Template:Vitamin


I don't see any real reason for having a seperate article on ascorbic acid, because vitamin C and ascborbic acid are one and the same, as pointed out in this article. Also, a bunch of chemical properties are already included, so I suggest removing sentences aluding to a non-existent ascorbic acid article. I'll leave that to the original authors though. I don't know how to wrap text around images, so the image I added is centered with nothing around it: a waste of space. Feel free to fix this. David E. Volk 16:37, 31 July 2007 (CDT)

Proposition: creation of the "Discovery of vitamin C"/"Discovery and history of vitamin C" page

The lengthy explanations on the history of vitamin c are interesting but could be displayed in a separate article. CZ has the article : "Discovery of pennicilin". I consider that "Discovery of vitamin C" would be an interesting page in its own right and could be the place to explore those problems surrounding vit. C's discovery and patenting and related issues (e.g. how scurvy was gradually accepted, how nascent globalisation of trade enabled the provision of never before seen amounts of vit. C in the northern latitudes, etc.). The page could also be more accurately called : "Discovery and history of vitamin C". A redirect from "Discovery of vitamin C" to "Discovery and history of vitamin C" or "History of vitamin C" could be used. Pierre-Alain Gouanvic 16:57, 13 November 2007 (CST)

Go for it. Chris Day (talk) 03:17, 19 November 2007 (CST)

The basic structure

The whole debate about recommended intakes is one thing, and of course Linus Pauling (and his 1971 paper) is at the center of the debate. Keeping an historical perspective is logical and useful. The fact that bowel tolerance varies in function of disease pertains to another logic, and to another section. Finally, the therapeutic uses are another section. No info will be suppressed in the process of structuring this article. Pierre-Alain Gouanvic 03:29, 19 November 2007 (CST)

...the 1974 paper. The reference has been included. Pierre-Alain Gouanvic 18:04, 19 November 2007 (CST)

The "Politics of Vitamin C" section

Was this a part of the original WP article? Because saying there is a conspiracy against Vitamin C seems awfully absurd (unless it actually is the case). Is it actually something that goes on? Also some things about the "Hypothesis" section seem equally dubious. --Robert W King 16:45, 19 November 2007 (CST)

It comes from WP. I agree. I'll work on that and will try to be constructive. Thanks for the input; I'll send you a notice when I it is done. Pierre-Alain Gouanvic 17:32, 19 November 2007 (CST)
A description of a nutrient includes its distribution in tissues and organs. This section will necessarily cover (part of) the debate on vitamin C requirements. Putting this in a separate "controversial" section would be biased.Pierre-Alain Gouanvic 21:08, 19 November 2007 (CST)

The "Vitamin C hypothesis" section

Many things in this section reflect a lack of understanding of who said what, etc. They will be moved in their respective sections on biosynthesis. Pierre-Alain Gouanvic 00:05, 20 November 2007 (CST)

In the following, all parts that are in italics are false, as we can judge by reading the biosynthesis section:
The fact that man possesses three of the four enzymes that animals employ to manufacture ascorbates in relatively large amounts, has led researchers such as Irwin Stone and Linus Pauling to hypothesize that man's ancestors once manufactured this substance in the body millions of years ago in quantities roughly estimated at 3,000–4,000 mg daily, but later lost the ability to do this through a chance of evolution. If true, this would mean that vitamin C was misnamed as a vitamin and is in fact a vital macronutrient like fat or carbohydrate. {Irwin Stone: "The Healing Factor"}
Dr. Hickey, of Manchester Metropolitan University, believes that man carries a mutated and ineffective form of the genetic machinery for manufacturing the fourth of the four enzymes used by all mammals to make ascorbic acid. Cosmic rays or a retrovirus could have caused this mutation, millions of years ago. {Hickey: "Ascorbate"} In humans the three surviving enzymes continue to produce the precursors to ascorbic acid but the process is incomplete and the body then disassembles them.
To be kept for future inclusion: the retrovirus hypothesis deserves its place; Irwin Stone's work, quoted in OMIM, too. Pierre-Alain Gouanvic 01:30, 20 November 2007 (CST)

Not useful in the intro, as it is in the chem box on its side

But the references will be useful:

also known by the chemical name of its principal form, L-ascorbic acid or simply ascorbic acid.[1][2] Pierre-Alain Gouanvic 00:57, 21 November 2007 (CST)

Idem: The guidance provided by the United States of America and Canada for Dietary Reference Intake (DRI) recommends 90mg per day and no more than 2g per day (2000mg/day).[3] Pierre-Alain Gouanvic 04:20, 21 November 2007 (CST)

Misplaced in the pharmacokinetics debate

Of course the following has to do with the debate:

Testing for ascorbate levels in the body Simple tests exist which measure levels of ascorbate ion in urine, serum or blood plasma. However, these tests do not accurately reflect actual tissue ascorbate levels. Reverse-phase high-performance liquid chromatography (HPLC) is used for determining vitamin C levels within lymphocytes and other tissue. It has been observed that while serum or blood plasma levels follow the circadian rhythm or short term dietary changes, levels within tissues are more stable and give a better determination of ascorbate availability within the organism. However, very few hospital laboratories are adequately equipped and trained to carry out such detailed analyses, and require samples to be analyzed in specialized laboratories. [4] [5]

... but this clearly deserves to be in the Distribution section. It will be important to provide a properly phrased link to the Distribution section. In +, the style doesn't have to be so colloquial. The example taken from diabetes is not especially useful: the article as it is now explains very clearly where, in the body, vitamin C is concentrated. Pierre-Alain Gouanvic 04:15, 21 November 2007 (CST)

General discussion on the acceptance of supplements

This burdens the page (see below, after the quote in italics). It's valid info, but it belongs to the "dietary supplement" page, some of it should really go in "consumer protection laws", "labelling", etc.

It will be possible to formulate concise and well referenced statements to replace this (there's only one ref, and its the conspiracy documentary. Worse than nothing, if it's not well supported (cf the comment by Robert W King, above)).

There exists research on the bias against Vitamin C in research, quoted by the famous Cochrane reviewer and researcher Harri Hemila: (http://www.cmaj.ca/cgi/eletters/174/7/937#4039)

Goodwin and Tangum (10) provided several examples to support the conclusion that there has been systematic bias against the concept that vitamins might be beneficial in levels higher than the minimum required to avoid classic deficiency diseases. Also, bias against vitamin C was documented by Richards (11,12) who compared the attitudes and arguments of physicians to three putative cancer medicines: 5-fluorouracil, interferon, and vitamin C. It seems that Pauling’s conclusions were dismissed because of the fundamental divergence with the traditional notion that the only purpose of vitamin C is to prevent scurvy (3) and not because of experimental findings. Evidently, carefully planned trials should be carried out to evaluate the potential role of high-dose therapeutic vitamin C on the common cold and cancer.


Removed section:

Advocacy arguments

Vitamin C advocates argue that there is a large body of scientific evidence that the vitamin has a wide range of health and therapeutic benefits but which they claim have been ignored. They claim the following factors affect the marketing and distribution of vitamin C, and the dissemination of information concerning the nutrient:

  • There is increasing evidence of the applications and efficacy of vitamin C, but governmental agency dose and frequency of intake recommendations have remained relatively fixed. This has lead some researchers to challenge the recommendations.
  • Research and the treatment approval process are so expensive, pharmaceutical companies rarely apply for approval of an unpatentable product. To do so without the protection of a patent would allow competitors to manufacture the product too, which would drive the price (and profit margin) down to a point much less desirable than the price point (and profit margin) of patentable products. The lower price would also reduce the likelihood of recuperating the company's exorbitant research funding and treatment approval costs. Vitamin C is not eligible for patenting because it is a natural substance, and because it has already been marketed to the public for some time. As of yet, no company has applied to the FDA (nor paid) for approval of vitamin C as a treatment for any disease.
  • Companies selling a treatment product are not required to inform consumers or patients of other treatments, even if those treatments are more effective, less expensive, and have fewer side-effects. Medical practitioners are not required to inform their patients of treatments for which treatment approval has not been granted. This situation, coupled with the label censorship explained above makes it more difficult to keep the public informed about the benefits of and new discoveries concerning the applications and effective dosage levels of vitamin C.
  • Matthias Rath and others point to low doses of vitamin C as the cause of the current epidemics of heart disease and cancer, and have termed the situation "a genocide", implying that health care providers (and particularly cardiologists and pharmaceutical companies) are aware of vitamin C's benefits and are deliberately seeking to block its acceptance as a therapeutic agent for financial gain.[111] He claims that governments have also colluded in this technology blockade by their expensive and bureaucratic systems of treatment approval which place barriers to new, inexpensive but not patentable approaches.

Reference 111:

  1. http://www.vitamincproject.com/ A conspiracy against vitamin C supplements has been underway for over three decades

(the end)

Pierre-Alain Gouanvic 04:38, 21 November 2007 (CST)

Scurvy

In parallel with the redefinition of vitamin C ("it is not simply the antiscorbutic vitamin"; Cf section 2 on allowances, in particular), the redifinition of scurvy was also suggested, by more researchers than one would imagine (I guess). In other words, some have adopted the point of view that there's more than scurvy, while others have developped the point of view that scurvy is more than what James Lind described (and that we don't really have a non-arbitrary definition for scurvy). "Subclinical scurvy" and other paraphrases are not so uncommon amongst clinicians.

It would probably be wise to develop an article on scurvy that would account for this evolution of the term and of the notion. A practical benefit: it would make the vitamin C article more concise and more about vitamin C. A methodological advantage: it would allow for more detailed pathophysiological considerations : low vitamin C associated with

- high histamine (cf the article on Barlow's disease)

- capillary fragility (in many tissues)

- bone fragility

- weakness and fatigue (carnitine deficiency; cf article)

- etc.

... an article with direct clinical implications.

Then, the vitamin C article would more easily welcome even more useful informations on its physiological roles, and better explanations for the layperson.

Of course, both articles would link to each other.

Pierre-Alain Gouanvic 10:47, 21 November 2007 (CST)

  • Axel Holst and Theodor Frolich--pioneers in the combat of scurvy

Tidsskr Nor Laegeforen. 2002 Jun 30;122(17):1686-7. [Axel Holst and Theodor Frolich--pioneers in the combat of scurvy] [Article in Norwegian] Norum KR, Grav HJ. ... Their findings were published in 1907 in the Journal of Hygiene, but caused scientific uproar since the concept of nutritional deficiencies was a novelty at the time. The crucial factor, Vitamin C, was discovered in 1930 by Albert Szent-Györgyi, for which he was rewarded the Nobel Prize. No prizes or proper recognition were awarded Holst and Frølich at the time. It took some 60 years before they due acclaim was given to them; the 1907 paper by Holst and Frølich is now considered the most important single contribution to elucidating the aetiology of scurvy. Pierre-Alain Gouanvic 17:48, 23 November 2007 (CST)

Fact check

In the description: "The D-enantiomer shows no biological activity." ambiguous. It can't be used as an enzyme cofactor, but it can be an electron donor (an antioxidant). It is not present in living things, if that's what it was supposed to mean. Pierre-Alain Gouanvic 11:44, 21 November 2007 (CST) "The active part of the substance is the ascorbate ion." Not a part. Pierre-Alain Gouanvic 11:46, 21 November 2007 (CST)

To do list

Sections that have not been changed since they were imported from WP:

  • Viral diseases (except hepatitis C)
in progress
  • Toxics: lead
  • Heart disease (except the first paragraph)
  • Autism
in progress
  • Obstetrics and gynaecology
  • Other effects (somethings come be put in a more appropriate place in the article, but only the hemodyalisis reamrk has been added)
  • Sources of vitamin C (Chris Day removed the tables, thanks! This was very heavy; the section on biosynthesis was mostly redundant; removed for now)

--Pierre-Alain Gouanvic 22:51, 30 November 2007 (CST)

Sections in progress

Section on evolution (biosynthesis)

At present, there are three considerations on the role and the impact of the inability to produce vit. C (in the article, Biosynthesis section). There exists other, possibly complementary, hypotheses (or "very suggestive observations") :

  • 1. Retroviruses, Ascorbate, and Mutations, in the Evolution of Homo sapiens Jack J. ChallemA, * and E. Will Taylor.
high oxidative stress =) high DNA mutation rate =)high evolution rate
and :
retroviruses=)DNA mutations=)including GLO deficiency (hypoascorbemia)

Pierre-Alain Gouanvic 17:15, 22 November 2007 (CST)

  • 2. Evolutionary significance of vitamin C biosynthesis in terrestrial vertebrates.
A Nandi, CK Mukhopadhyay, MK Ghosh, DJ … - Free Radic Biol Med, 1997
Evolution of vertebrates from aquatic medium to the terrestrial atmosphere containing high concentration of environmental oxygen was accompanied by tissue-specific expression of the gene for L-gulonolactone oxidase (LGO). ...
SOD vs GLO. When SOD increases, GLO decreases; ontogeny recapitulates phylogeny: high GLO during postnatal period (amphibians, early 4 tetrapods); "significantly higher plasma SOD and CAT activity in older individuals than in younger individuals. The induction in activity of SOD and CAT during human aging may be a compensatory response of the individual to an increased oxidative stress.
To evaluate further the nature of these enzymes in antioxidant defense, gene knockout mice deficient in copper-zinc superoxide dismutase (CuZnSOD) and GSHPx-1 have also been generated in our laboratory. These mice developed normally and showed no marked pathologic changes under normal physiologic conditions. The nature of antioxidant defense mechanisms: a lesson from transgenic studies. Environ Health Perspect. 1998 Oct;106 (they do have GLO.)
   The nature of antioxidant defense mechanisms: a lesson from transgenic studies.
Similarly, increased expression of extracellular SOD or glutathione peroxidase, as well as supplementation with SOD mimetics has been found to protect the CNS from a variety of neurotoxins (28, 29). In more simple models, overexpression of SOD and catalase significantly extended the lifespan of flies and worms ... Remarkably, up to 60% of the lifespan of SOD knockout and catalase knockout Drosophila can be restored by expression of SOD in only the motor neurons (32). Oxidative stress and nitration in neurodegeneration: Cause, effect, or association? http://www.jci.org/cgi/content/full/111/2/163
also see Ascorbic Acid: Biochemistry and Biomedical Cell Biology, James R. Harris, p. 157 (Dabrowski, 1994)
  • 3. Vitamin C: the primate fertility factor? J MILLAR - Medical hypotheses, 1992
  • 4. l-gulonolactone oxidase, a microsomal enzyme that catalyzes the terminal step in the biosynthesis of l-ascorbic acid is missing in most primates. Consequently, these organisms are prone to scurvy if the concentration of vitamin C in the diet falls. Paleopathological markers for the diagnosis of scurvy in ancient human skeletons have been described (22), but there is no paleopathological evidence of scurvy (or any other vitamin-specific dietary deficiency) among the Neanderthals or other fossil hominids. A molecule of l-ascorbic acid is consumed for each hydroxylation event (23). With an omnivorous dietary adaptation, especially a shift toward greater carnivory, there are periods when dietary vitamin C would either not be available or present only in reduced amounts. Recent humans, chimpanzees, and orangutans are omnivores; therefore, this difference in the posttranslational hydroxylation of osteocalcin compared to the herbivorous gorilla may relate to increased selective pressure to limit hydroxylation to counteract periods of low dietary vitamin C.

Osteocalcin protein sequences of Neanderthals and modern primates http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15753298

  • 5 (uric acid): Humans have higher serum levels of uric acid as compared with mice due to the loss of uricase activity.18 Uric acid may therefore aid in preserving ecSOD activity in humans at physiological levels. cf 2. Toward Understanding of Extracellular Superoxide Dismutase Regulation in Atherosclerosis http://atvb.ahajournals.org/cgi/content/full/22/9/1367
  • These pseudogenes (gulo human & guinea pigs) are unique in that they are not accompanied by their functional gene in the genome, as are most pseudogenes Ascorbic Acid: Biochemistry and Biomedical Cell Biology, p35 (??)
Pseudogenes: Genes bearing close resemblance to known genes at different loci, but rendered non-functional by additions or deletions in structure that prevent normal transcription or translation. When lacking introns and containing a poly-A segment near the downstream end (as a result of reverse copying from processed nuclear RNA into double-stranded DNA), they are called processed genes. (MeSH)


  • Z. "the primate L-gulono-gamma-lactone oxidase genes are a typical example of pseudogene" Random nucleotide substitutions in primate nonfunctional gene for L-gulono-gamma-lactone oxidase, the missing enzyme in L-ascorbic acid biosynthesis.Biochim Biophys Acta. 1999 Oct 18;1472(1-2):408-11. Ohta Y, Nishikimi M.

Section on "as an enzyme cofactor"

"Unlike other water-soluble vitamins, ascorbate is not specifically required for the functioning of ANY enzyme, and its exact physiological role is unkown" (then follows a rather long list of enzymes which use ascorbate). p158 (ibid) Pierre-Alain Gouanvic 17:56, 22 November 2007 (CST)

Section on the sociology of vitamin C

Criticism of animal models of disease

It has been argued that only primates, the Shionogi (ODS) rat, and guinea pigs are vitamin C-deficient species, that can be used in animal experiments to model human disease. This is a very radical issue. This absolutely has to be in the article. Pierre-Alain Gouanvic 17:42, 23 November 2007 (CST)

Mice unable to synthesize vitamin C should become valuable research tool, scientists say (May 16, 2000 -- No. 282):
""The value of the mice Dr. Maeda has made is that they are now in a sense ‘humanized.’ That means experiments with them can combine the dietary things that have long been possible with guinea pigs with the marvelous genetic experiments that are possible only with mice." (...) " The two scientists have been developing a deeper understanding of the genetic basis of atherosclerosis, commonly known as "hardening of the arteries." The condition involves fatty deposits building up on artery walls and restricting blood flow to the brain, heart and other parts of the body. A complex disease that affects people differently, atherosclerosis is the leading cause of death in the United States, and more than half the population suffers from it eventually."
Pierre-Alain Gouanvic 18:08, 23 November 2007 (CST)

Bias in vitamin C research (section)

Most medical interventions are submitted to a careful assessment of the evidence, where theoretical work, and clinical studies are weighted by competent experts in the field. The diffusion of the information on the theoretical work, and clinical studies in the media only plays a minor role, since patients will only receive what has been approved by specialists. With vitamin C supplements, the most sold supplements in the world, things are turned upside down. Research is published, mediatized, causes changes in public opinion (and doctor's opinions), it is later assessed by experts, often retracted or put in context (vit. C and cancer, oxalate, cataracts, so forth), but this doesn't get to the public, who remains with misconceptions (junk science).


  • Research made by researchers who have specialized on (and sometimes patented) competing molecules
Definition of a conflict of interest in the context of non-patentable products versus patentable products (different from COI in the appraisal of patented products)
cf cataract, anticancer medications
The smart food market of innovation
Linus Pauling Institute vs Linus Pauling
Vitamin C has dose-dependent effects; the UL is criticized by experts; the RDA as well; neglecting this fact allows specialists in different fields of free radical research to continue to work on their own speciality, without setting priorities. The priorities of the market of innovation are different from citizen's priorities.
  • Logical fallacies:
Research based on hypotheses but not on pathophysiology:
1. Oxalate (does oxalate excretion mean oxalate deposition? Also see hemodyalisis)
2. Oxidants are good, so antioxidants are bad
3. Vitamin C is part of a complex antioxidant machinery, so only cocktails should be studied
violation of scientific protocol
4. Whole foods are better than supplements, so vitamin deficiencies are not treated, but smart foods (patented products) are developped
5. The Fenton reaction (not adressing metal overload, or posing vitamin C (even when deficient) as a problem when metal overload is)
6. Antioxidants behaving as oxidants
In viruses and bacteria: part of their specific microbicidic activity, not proof of their dangers
Incomplete treatment of a deficiency; letting a deficiency state cause aberrations in redox metabolism
  • Bandwagon fallacy: "Surfing" on misconceptions and media hype
Cf most of the above
  • Appeal to fear: Playing with the fear of self-medication
Implies that it is better to let people in a deficient (subnormal) state than to let them self-medicate
Mistaking complementary measures with alternative measures
Treating the patient as more irresponsible than s/he is to push the argument of authority.
  • Strawman arguments (answering the wrong question): Not taking in consideration markers of oxidative stress or tissue vitamin C status (no valid endpoints)
Reference : Proof versus plausibility (...), Hoffer, John. CMAJ; Hemila on Vit. C in colds and cancer: is the dosage issue publicly stated? Or is it only disclosed in medical journals ?
  • Ad Hominem arguments:
Attacks to the reputation of Linus Pauling (senility, obsessive interests) remain in the public discourse, despite of proof of the contrary
The history of Vitamin C's appraisal is closely tied with the history of Linus Pauling's mental health appraisal
The virucididal, virus replication-inhibiting activity of vit. C remains largely unadressed, while Matthias Rath becomes an infamous celebrity.
  • Denial
The evolutionary basis. "Nothing makes sense in biology except in the light of evolution." (Dobzhansky) The decline in vitamin C consumption in the evolution of man is by far the greatest dietary decline in his evolution (at least as far as vitamins are concerned; Cf Pauling, 1974, Milton (both already quoted)). Research doesn't reflect this fact.

Pierre-Alain Gouanvic 09:22, 24 November 2007 (CST) Pierre-Alain Gouanvic 11:23, 24 November 2007 (CST)

The Sociology of vitamin C section appears coherent and open for discussion. Much has been said in not so many words (good supporting references). Many of the themes above will find their way elsewhere. --Pierre-Alain Gouanvic 22:57, 30 November 2007 (CST)

Clustering of diseases in categories

Presentation of the pathophysiological rationale for each section

  • Viral diseases
Colds, others (cf Harakeh et al.)
  • Cancer
  • Toxics
Insecticides, heavy metals
  • Liver diseases
Hepatitis, non-alcoholic fatty liver disease and carnitine-deficiency-associated diseases
  • Brain diseases and psychiatry
Autism, stress-associated diseases (including libido), stroke, addictions
  • Ocular diseases
cataract, others
  • Heart disease
the Shionogi (ODS) rat and related items.
Halfway through; some formatting has to be done!
--Pierre-Alain Gouanvic 01:45, 26 November 2007 (CST)

Transfer to biosynthesis

... if it is not redundant:

Animal sources

The overwhelming majority of species of animals and plants synthesise their own vitamin C. Synthesis is achieved through a sequence of four enzyme driven steps, which convert glucose to ascorbic acid. It is carried out either in the kidneys, in reptiles and birds, or the liver, in mammals and perching birds. The last enzyme in the process, l-gulonolactone oxidase, cannot be made by humans because the gene for this enzyme is defective (Pseudogene ΨGULO). The loss of an enzyme concerned with ascorbic acid synthesis has occurred quite frequently in evolution and has affected most fish; many birds; some bats; guinea pigs; and most primates, including humans. The mutations have not been lethal because ascorbic acid is so prevalent in the surrounding food sources (it may be noted that many of these species' diet consists largely of fruit). Pierre-Alain Gouanvic 12:17, 24 November 2007 (CST)

In the RDA section

No RDAs for the non-healhty and not-so-healthy, role of stress in vit C depletion (see distribution -- Adrenals); implications:

(removed from Food sources -- unless cannibalism is an option, there's no reason to have this there)

Trauma or injury has been demonstrated to use up large quantities of vitamin C in animals, including humans. [6]

Opening sentence unclear

Is Vitamin C the only required vitamin, and this only by a minority of animals, of which humans are one? Or Do the majority of animals require all the vitamins, and only a minority, including humans, only require vitamin C? Actually, neither of the above would seem to me to be true, but that's what the opening appears to say. Can someone clarify? Aleta Curry 15:22, 25 November 2007 (CST)

I would suggest something like:
Unlike other vitamins, which are required by the majority of animal species, vitamin C is only required by a minority of animal species, including humans and higher primates.
Would you say it's better?
Pierre-Alain Gouanvic 15:33, 25 November 2007 (CST)
Yes, much better, clear and to the point.Aleta Curry 15:38, 25 November 2007 (CST)

MUST be added to the article

The molecule was first called by Albert Szent-Gyorgyi "ignose, meaning ì don't know, or godnose, but the editor of the journal (...) did not appreciate such humor" Adult Scurvy J AM ACAD DERMATOL, DECEMBER 1999

Nomen est omen! Pierre-Alain Gouanvic 16:03, 25 November 2007 (CST)

Done! (In the intro). Except that i couldn't use the latin quotation (Nomen est omen)
--Pierre-Alain Gouanvic 23:01, 30 November 2007 (CST)

From the early "politics of vitamin C" section

Since its discovery vitamin C has been considered a universal panacea by some, although this led to suspicions of it being overhyped by others. [7]

In the 1960s Nobel-Prize winning chemist Linus Pauling, after contact with Irwin Stone, began actively promoting vitamin C as a means to greatly improve human health and resistance to disease. His book How to Live Longer and Feel Better was a bestseller and advocated taking more than 10,000 milligrams per day. It sold widely and many advocates today see its influence as the reason there was a marked downward trend in US heart disease from the early 1980s onwards.

Stone's work also informed the practise of Dr. Robert F. Cathcart III, in the 1970s and 1980s. He applied extremely large doses of ascorbate (300 grams = 0.66 pounds per day) to a wide range of viral diseases with successful results. Cathcart developed the concept of Bowel tolerance, the use of the onset of diarrhea as an indication of when the body's true requirement of ascorbic acid had been reached. He found that seriously ill people could often tolerate levels of tens of grams per day before their tolerance limit is reached.

Matthias Rath is a controversial German physician who once worked with Pauling. He is an active proponent and publicist for high dose vitamin C. He has published a theory that deaths from scurvy in humans during the ice age, when vitamin C was scarce, selected for individuals who could repair arteries with a layer of cholesterol. He theorises that, although eventually harmful, cholesterol lining of artery walls would be beneficial in that it would keep the individual alive until access to vitamin C allowed arterial damage to be repaired. Atherosclerosis is thus a vitamin C deficiency disease. Rath has also argued publicly that high doses of vitamin C can be effectively used against viral epidemics such as HIV[8], SARS and bird flu[9][10].

It has been suggested by some advocates that ascorbic acid is really a food group in its own right like carbohydrates or protein and should not be seen as a pharmaceutical or vitamin at all. {Irwin Stone: "The Healing Factor"}

transporters

For the SVCT transporters, I think you should mention the affinity and what that means in the context of biological concentrations. Also how does it compare to glut1 and the other gluts. For the GLUT transporters you only mention glut1. This is important when discussing the brain paradox because other gluts are in present in other tissues as well as all the SVCT's. The real key here, I presume, is that the affinity for GLUT1 is much higher than for all other transporters, even higher than SVCT?, and hence the brain gets much more of the available vitC. I'm guessing here but I know the GLUT1 affinity for glucose is much higher than for the other GLUTs, so I see no reason why the same is not true for vitC.

I'll analyze Wilson JX (2005). "Regulation of vitamin C transport". Annu. Rev. Nutr. 25: 105–25. PMID 16011461., reference #17, to try to address the issues that you raise. Thanks for emphacizing those problems! I was aware that GLUT types had to be dealt with. I'll provide the data on affinity, and show what it means.
The differences in insulin dependence of various tissues could play an important role in explaining many things, especially the brain paradox.

The paper you cite appears to conclude that "by transporting oxidized vitamin C, allows important organs to quickly store vitamin C in times of increased oxidative stress." This seems quite speculative, trying to correlate a fact with a putative reason (vitC is good for antioxidative properties). Is there a back up from later sources for such a comment? I can see the physiological reason for the high affinity for glucose, it's the only food source for neurons, but surely the high affinity for oxidised ascorbate is a secondary effect of the need for glucose? Or is the Km for oxidised ascorbate independent of the Km for glucose? Chris Day (talk) 03:02, 26 November 2007 (CST)

I don't known of any research that followed which reinforced those statements, but i think the reason for this is that researchers rarely utter finalistic arguments ("trying to correlate a fact with a putative reason", as you described).
The authors state that, at 60 mg of vit. C intake, there are vanishingly low levels of DHA; these levels only raise when oxidative stress tilts the AA/DHA balance. We could formulate things differently based on this.
The problem is that humans are the only species who consume, in comparison, vanishingly low amounts of vitamin C. Current pharmacokinetic data do not support the belief that gorillas excrete "expensive urine". Deriving broad conclusions about physiology based on dietary intakes set by (some) humans is a logical fallacy. I think that there's good evidence that, in other hypoascorbemic species, both AA and DHA are higher in the blood. Those are important data that i (or others) will have to provide.
Another issue is that the oxidation of ascorbic acid continually takes place, and research should identify what portion of it is recycled, what portion is transported in the brain, in urine, etc. As far as I know, nothing has been done to provide such a broad picture.
In terms of evolution, what would be the physiologic reason for taking either glucose, or an antioxidant precursor? I know of another instance where there is a trade-off between energy provision and antioxidant provision. Pyruvate can either be a substrate for oxidation or... a substrate for oxidation -- an antioxidant:
Secretion of pyruvate. An antioxidant defense of mammalian cells. J O'Donnell-Tormey et al. Journal of Experimental Medicine, Vol 165, 500-514
The rate of pyruvate accumulation was almost doubled in the presence of exogenous catalase, suggesting that released pyruvate functions as an antioxidant... Extracellular pyruvate was in equilibrium with intracellular stores. Thus, cells conditioned the extracellular medium with pyruvate at the expense of intracellular pyruvate, until homeostatic levels were attained in both compartments.
In other words: there is a coupling between oxidation and "antioxidation". The pyruvate used to eliminate oxidants is not used to produce oxidants through energy metabolism; the antioxidant glucose derivative (ascorbate) that is transported competes with glucose, a source of oxidants.
There's a similar interplay with glutamate: glutamate, the major excitatory transmitter, either causes the production of potentially toxic levels of oxidants (eventually leading to excitotoxicity) or is allocated to glutathione synthesis (GLU-CYS-GLY). Glutamate transport is the crucial issue here. There's also a coupling between ascorbate transport and glutamate transport in the brain (heteroexchange). Fascinating and enlightening phenomenon. Some references explore the pheomenon; this definitely deserves to be clearly put in the article.
First, I'll analyse closely the most relevant literature to get a clear picture, and perhaps these considerations will look more like reasonable inferences and less like personal insights?
Oh, the authors of the study also raise the possiblity that catecholamies could be involved (vit C is involved in catecholamine synthesis). They give much more importance to the antioxidant role of vit. C, however : (concluding sentence of the abstract:) "These results have implications for increasing antioxidant potential in the central nervous system." No mention of catecholamines.
Also, why the transport of oxidized vitamin C rather than vitamin C?
In order to get rid of the finalistic argument, it could be useful to show that this entrapment is an evolutionarily conserved method to keep vitamin C in compartments, without the risks associated with the maintenance of transporters, such as SVCTs, which could allow vit. C to leave compartments although it let it in in the first place. The given compartment keeps as much vitamin C as it can recycle (from DHA). The PNAS study revealed that high AA levels could be reached with DHA administration, without evidence of an oxidant overload.
--Pierre-Alain Gouanvic 15:35, 26 November 2007 (CST)
i don't have time to digest all your info here but with respect to "Also, why the transport of oxidized vitamin C rather than vitamin C?"; this is an interesting question. Without reading around the topic my assumption is that SVCT's are the primary transporter and GLUT's are a secondary transporter. I assume that the oxidised form is quite similar to the glucose topology whereas the vit C is not. If true, then the oxidised vitC affinity for GLUT's might be proportional to the glucose affinity and GLUT1 might be serendipidously more efficient at transporting the oxidised vitC than the equivalent SVCT. Possibly the brain SVCT is even not present due to its function being lost in that tissue in preference to GLUT1 function? (excuse all the wild speculation but this is not my area.) So far, this section raises far more questions for me than being informative. Now, after all my wild speculation, I'll try and find the real kinetics and expression patterns for these transporters. I'll read the review you link to above too. Hopefully we can find some more concrete reviews with regard to the brain paradox and the significance of GLUT1 in that role. Chris Day (talk) 16:18, 26 November 2007 (CST)
I'm getting my GLUT transporters mixed up, GLUT1 is not brain specific and not the one with the very low Km. After a bit of reading is is clear that not all GLUT's can transport oxidised vitC; only GLUT1,3 and 4. One thing i had not got straight was that SVCT is specific for reduced form. I found an interesting paper by Montecinos V, et al. Vitamin C is an essential antioxidant that enhances survival of oxidatively stressed human vascular endothelial cells in the presence of a vast molar excess of glutathione. J Biol Chem. 2007 May 25;282(21):15506-15. Epub 2007 Apr 2. PMID 17403685. More thoughts later. Chris Day (talk) 17:47, 26 November 2007 (CST)
The paper by Wilson is very dense.
So, yes, SVCTs and GLUTs transport AA and DHAA, respectively. I think that the following, another paper by Vera & al (the one you suggest is one of the latest of great researches by Vera and colleagues), is very useful: Nualart FJ et al Recycling of vitamin C by a bystander effect. J Biol Chem. 2003 Mar 21;278(12):10128-33. Epub 2002 Nov 14.
PMID: 12435736.
I hope you don't mind if I quote extensively; I also used bold characters which might look a little "agressive". Sorry!
(to read the quote, click "edit" for this section ("transport") and scroll down to this location; the quote has been put in the background to facilitate an overview of the discussions)--Pierre-Alain Gouanvic 11:51, 27 November 2007 (CST)
This certainly must be taken into account when analyzing affinities and concentrations.
--Pierre-Alain Gouanvic 20:40, 26 November 2007 (CST)
I'll read that one too. Just for onlookers, I'm not proposing to go into detail like this in the article, but to get an accurate redux of the current knowledge it is important to know exactly what the data is in these papers as well as the conclusions they are drawing from their data. Hopefully the final paragraph will be accessible to all. Chris Day (talk) 23:30, 26 November 2007 (CST)

Still much WP content to edit

Sections that have not been changed since they were imported from WP:

see TO DO list, above. --Pierre-Alain Gouanvic 22:51, 30 November 2007 (CST)

What about to divide an article Vitamin C and Ascorbic acid?

What do you think, if we create the new article - Ascorbic acid (today it is only redirection), where we write all data about chemical substance?

Both articles can have great volume - this we write all about biochemistry and effects of Vitamin C,

- and the new, the chemistry of Ascorbic acid (from CAS and density to industrial synthes and reactions) is also not a small and deserve the own article? Alexander N. Alexandrov 04:11, 4 December 2007 (CST)

Yes, indeed!! I would think of providing the following info:
* how it is used regularly used in vitro in a free radical-generating system (Fe-ascorbate) (perhaps in the "reactions" sections that you are suggesting
* its reducing power
* its reactivity with various oxidants ("perferryl radical"(?)(cf Chatterjee), superoxide, not only hydroxy...))
* as you said, industrial synthesis (bacteria, new methods under development)
If you want to begin right away, I encourage you. I don't know how to a edit a redirect page!!
--Pierre-Alain Gouanvic 14:34, 4 December 2007 (CST)
Your wish is my command. You guys better get cracking on this, (mark yourselves down at the write-a-thon page), or else I'll look like a right idiot! Aleta Curry 15:49, 4 December 2007 (CST)
 :-)
I look to english WP and see new there are all 2 ariicle in it!
So it can be stub for us to the first time... Alexander N. Alexandrov 01:47, 5 December 2007 (CST)
I'm moving some info right now to the asc ac page. I hop it wont conflict too much! --Pierre-Alain Gouanvic 01:51, 5 December 2007 (CST)
Yes, edit conflict. But I'll let you do the move! It's a much better idea. --Pierre-Alain Gouanvic 01:54, 5 December 2007 (CST)
 :-)
My first questions:
- is categories tree in Citiz really empty today?
Categories are not used here. There have been a few discussion on the forums on this topic.
- is Citiz proect only in english today? Alexander N. Alexandrov 01:57, 5 December 2007 (CST)
Yes, again there has been discussion about other languages on the forums.
- and the Template:Inuse also absent? Alexander N. Alexandrov 02:11, 5 December 2007 (CST)
I'm not sure what this template is for in wikipedia but you can copy it from wikipedia and bring it here if you need it. Is it used in this article? Chris Day (talk) 02:59, 5 December 2007 (CST)
May be... Thanks! Alexander N. Alexandrov 03:06, 5 December 2007 (CST)

References

  1. Food Standards Agency (UK) on vitamin C
  2. University of Maryland, Medical Center Vitamin C (ascorbic acid). Accessed January 2007 C
  3. US Recommended Dietary Allowance (RDA) (pdf), Page 6 on vitamin C. Accessed January 2007
  4. Emadi-Konjin P, Verjee Z, Levin A, Adeli K (2005). "Measurement of intracellular vitamin C levels in human lymphocytes by reverse phase high performance liquid chromatography (HPLC).". Clin Biochem 38 (5): 450-6. PMID 15820776.
  5. Yamada H, Yamada K, Waki M, Umegaki K. (2004). "Lymphocyte and Plasma Vitamin C Levels in Type 2 Diabetic Patients With and Without Diabetes Complications" (PDF). Diabetes Care” 27: 2491–2.
    the plasma concentration of vitamin C is considered to be strongly correlated with transient consumption of foods. The measurement of lymphocyte vitamin C might be expected to be a more reliable antioxidant biomarker than plasma vitamin C level. In this report, we demonstrated that the lymphocyte vitamin C level is significantly lower in type 2 diabetic patients, but we could not observe such an association in plasma vitamin C levels. In diabetes, therefore, the measurement of lymphocyte vitamin C might be expected to be a more reliable antioxidant biomarker than plasma vitamin C level.
  6. Ascorbic acid dynamics in the seriously ill and injured. Journal of Surgical Research, Volume 109, Issue 2, Pages 144–148 C. Long. - "Our results show that plasma ascorbic acid levels following trauma and during infection are extremely low and are not normalized with 300 or even 1000 mg/day supplemented TPN. " Accessed January 2007
  7. Hemilä H., "Do vitamins C and E affect respiratory infections?" Univ. of Helsinki, Dissertation, Faculty of Medicine, Dept. of Public Health. 2006.
  8. Nigeria: Vitamin C Can Suppress HIV/Aids Virus all Africa.com 22 May 2006, accessed 16 June 2006
  9. Discredited doctor's 'cure' for Aids ignites life-and-death struggle in South Africa Saturday May 14, 2005 The Guardian
  10. Open letter from Dr. Matthias Rath MD to German Chancellor Merkel Rath's own website 2005, downloaded June 2006

sources

  • Dolske, M.C., et al. (1993), A preliminary trial of ascorbic acid as a supplemental therapy for autism. Prog. Neuropsychopharmacol. Biol. Psychiatry, 17(5):765–774.
  • Green, V.A., K.A. Pituch, J. Itchon, A. Choi, M. O'Reilly, J. Sigafoos, (2006), Internet survey of treatments used by parents of children with autism, Res Dev Disabil, 27(1):70–84.

I moved the references above from the main article (sources section) with the intention of merging to the bibliography. However, the two above seem to be references that are cited in the article. These should probably be inserted in the appropriate places in the text between ref tags (<ref></ref>). Chris Day (talk) 11:53, 6 December 2007 (CST)

Done! --Pierre-Alain Gouanvic 13:02, 6 December 2007 (CST)

In hand?

I received a complaint from an author about this article. Can I assume that the editors here have matters well in hand? If not, please e-mail me. --Larry Sanger 09:33, 3 January 2008 (CST)

One other point, as yet another author has lodged a complaint: if, in the opinion of an editor in one of the relevant workgroups, the article is of very poor quality, whether due to factual errors, amateurish descriptions, or bias, the editor can remove the article (or offending sections of the article), placing it on a subpage (e.g., Vitamin C/Sections to rework) or simply the talk page. (Probably not the latter in this case as the talk page is already very active...) We have done so in the past and it is a solution I favor, rather than risking further embarrassment of our editors.

The following strikes me as obviously (by the very nature of the claim) biased: "The history of vitamin C research provides remarkable examples of amateursim [sic]." The whole point of the picture that is captioned, "Galileo, a 'dangerous enemy' of the elites, committed the crime of writing for the masses," is obviously to make a certain argumentative point. The claim, "Citizens, philosophers of sciences and ethicists have been called to duty in the struggle for accountability in biomedical sciences," implies that the article expresses what the duty of citizens et al. actually is--and that is the sort of thing that Citizendium articles may not do. Whatever its merits, this editorializing is inconsistent with CZ:Neutrality Policy. Any points, or axes that are being ground, must be attributed to specific people, with contrary views being stated fairly, in proportion to their popularity among experts on the subject.

if it isn't removed/edited by tomorrow, I'll remove it myself

--Larry Sanger 22:02, 3 January 2008 (CST)

These are sections that gave me much trouble. I remove everything (Sociology and Future research) for now, instead of editing, and I will try to find colleagues in CZ who could help me with these issues. I agree that those sentences were too argumentative, but the more informative parts and the references are, I think, important and useful. They will be found on my talk page.

I have received some comments in the past regarding the analysis of the reception of vitamin C, the marginalization of Pauling, this "dangerous enemy" thing (this is a quote from an article in the Archives of Internal Medicine) etc., I understood from these comments that the content was valid, but that I had to be careful not to exaggerate. I'll be much more cautious in the future.

In the future, I would really appreciate to receive comments, criticisms and complaints.

Last thing. I was impressed by the good reception I received on the article Evidence-based medicine. I can see now that I had been more cautious when dealing with editorial comments. I made it clear that they weren't mine, not those of CZ. They were accepted almost unmodified.

I'll try to behave as much as possible in the same way.

I'll check the rest of the article.

Pierre-Alain Gouanvic 00:07, 4 January 2008 (CST)

Thanks very much indeed for that! --Larry Sanger 09:16, 4 January 2008 (CST)

suggestions

IMHO, the article should focus on five things: scurvy, RDA values, side effects/contraindications, natural sources and biosynthetic pathways.

Then, somewhere have a sentence or two describing the fact the Vitamin C has been suggested to be useful for the treatment/prevention of viral diseases, cancer, heart disease, etc., and have a link to a subpage(s) with all of this information. If possible, link these sentences somehow with physiological (organ?) distributions of vitamin C, as they are probably related somewhat. Finally, a "Discovery and History" supbage could be used to explain the discover and continuing controversies of vitamin C.

Plan of action: Move the whole page to "things to work on", and then work on and bring back one section at a time. I will the actual page removal to an editor in the Heath Sciences field.

Finally, the whole controversy aspect is overblown. Every drug/suppliment ever suggested for human use has had proponents and detractors. Pauling's name seems to give it more credence, perhaps too much so. David E. Volk 09:14, 4 January 2008 (CST)

Breakdown in editorial process

I can't help but wonder that if there had been more editorial guidance in the development of this article, it wouldn't have come down to this little soiree of disagreement. I think this might be a pretty good example of a failure of the process. --Robert W King 09:22, 4 January 2008 (CST)

good example of editorial process

Oddly, I disagree, and think that this is a good example of why the CZ process will prevail. Namely, that eventually every article must pass through editorial hands, as is typically done with all excellent published material. Personally, when I write or edit, I find it best to write alot and trim down, and that is what will happen with this article. David E. Volk 09:32, 4 January 2008 (CST)

I don't disagree David, it's definately good that it should be handled, but I'm hypothesizing that perhaps if there had been more editor interaction earlier on, there would not have been as much work to do now as there is. --Robert W King 09:37, 4 January 2008 (CST)
I just want to point out that I saw there were some problems early on but I also recognised the article was very embryonic. Sometimes it is best to let the first draft develop and then start the collaboration process. The only problem I can see if approval goes ahead without editorial oversight. Chris Day (talk) 16:14, 4 January 2008 (CST)

My recent edits

I have made some substantial deletions. I'm sorry to be destructive in these rather than constructive, the article has a lot of interesting and lively content, but I feel that it goes beyond an encyclopedic article and into the realm of promotion. The cuts that I have made, which are illustrative rather than comprehensive, were the following

On tissue distribution I cut the sections on hypothalamus and hippocampus; they add little to what is said of brain generally, but the section on hippocampus by drawing attention to its role in memory appears to be there to suggest by association a beneficial effect on memory. One of the hypotheses about Alzheimers is that it reflects oxidative damage by free radicals, and so it might be conceivable that antioxidants could prevent or delay such damage. This is only one of several hypotheses and there is no clear evidence that Alzheimer's can in fact be prevented.

I cut this because I think that Citizendium must always be ultra cautious before ever stating anything that could be taken as "medical advice"; it must not be our job to promote remedies, even when there is good evidence of their efficacy, much less when the evidence is only suggestive. Especially we must not raise hopes among vulnerable readers by appearing to promote hypothesised cures for which there is not solid evidence. We must I think err on the cautious side in avoiding to seem to be offering advice to readers.

Accordingly I cut the section on lung cancer, although there may be a case for including this within an article on lung cancer. In general I think that the sections on health benefits should be drastically reduced, with only those that have been given serious study discussed.

I cut the text reporting the views of Hickey essentially because this is not a peer-reviewed source and I was not confident that the critique that was reported reflects generally accepted views.

I cut the text regarding Cathcart's paper; this was published in "Medical Hypotheses". This journal was (and may still be?) specifically a vehicle for airing controversial, non-established views. It should not be taken as a mark of authority, indeed perhaps the opposite. Gareth Leng 13:00, 4 January 2008 (CST)

Hi,
I can tell you that, in fact, I appreciated that you do much of the job of removing unsatisfactory parts of the article. I removed another large part myself, with explanations in the page history. I'll continue to look. I also appreciate that you had kind words about my work.
I feel that it is time for me to get back to the most difficult, but most fascinating part of the work I want to do in the vit C page (and others as well): find high quality research and develop (with others) the most brilliant analysis of the literature on its various physiological roles/effects.
I regret I did not stay on this course. For example, Chris Day visited the page to provide help about vitamin C transport; I have to work more on this with his advice in mind.
Concerning the whole therapeutic uses section, and the risk of stating medical advice, I'll let others provide their perspective if they feel that it is debatable, and take yours as the consensus for now. I think that I agree with you (as in the example of lung cancer) that much of the research on vitamin C in diseases can be transferred in the relevant entry -- on the given disease (section: Aetiology, and/or Pathophysiology perhaps Treatment). But, taking the example of lung cancer, I am sure that those results could be used by readers in a manner that could lend some to believe that the CZ provides medical advice. This might happen in several other cases. Most people are aware that non patented medications and molecules are not researched as aggressively as patented ones, and they will compensate for this by using their judgment and their doctor's advice. My experience with doctors tells me that things work this way increasingly. What should CZ do about this? Protectecting vulnerable readers is important, but isn't a responsibility shared with other actors, such as the physician?
But, again, this is only an opinion, that I could explain and defend if a discussion takes place. I'll focus on physiology and (eventually) address diseases one at a time, article after article (if there a good reason to do so, if it doesn't appear too promotional).
Finally, one deletion that occurred a little bit earlier could eventually be reversed, with some editing perhaps. In the intro, I stated something perhaps a little mysterious -- I had not elaborated yet in the body of the article:
It is also the only water-soluble vitamin whose exact function remains unknown, although it has numerous physiological effects and eight different well characterized roles.[1]
The reference is a book (Ascorbic acid: biochemistry and biomedical cell biology

James R. Harris, ed.; accessible through Google books), and I had not indicated the page. Here is the excerpt (p 158):

Unlike other water-soluble vitamins, ascorbate is not specifically required for the functioning of any enzyme, and its exact physiological role is unknown. (Then follows, in this excellent article, a long list of functions/effects/roles that it has, at physiological concentrations).
I think it is very important for the coherence of the intro, and for a proper understanding of the inherent difficulty in covering human knowledge about this molecule. This is, in my opinion, a good starting point for a topic as huge and challenging as vitamin C.
Pierre-Alain Gouanvic 03:23, 5 January 2008 (CST)
Your explanation made sense, and with a little expansion to restore this would be fine by me. I merely cut it because I felt it questionable whether it could be said that the exact physiological function (rather than biochemical function) is known for all other vitamins.Gareth Leng 12:53, 5 January 2008 (CST)
Great! Pierre-Alain Gouanvic 13:12, 5 January 2008 (CST)

The constraint to produce the vitamin

Hello Pr Leng,

I see that you have been working very intensely on the page, and I don't want to interrupt. Actually, I am, also, working on different things (the various enzymes acted upon by ascorbate -- "cofactor" might be too strong, at least according to some authors, I'll get to this later). I'd like to discuss one edit when appropriate. It can be accessed here. I wrote:

Since vitamin C, in plants like in animals, is used to resist many environmental challenges, it is logical that cultivation, with its associated pest control and controlled environment, lessened the need for endogenous vitamin C production in plants.

This sentence refers to an ealier assertion, in the Biosynthesis section:

Plants, humans' main source of vitamin C, produce it in large amounts. Plants use vitamin C in such great amounts as a defense to survive to viruses, bacteria and other environmental challenges and to cope with the internal challenges associated with photosynthesis.8 (form this source: "Plants produce large amounts of L-ascorbic acid to facilitate resistance to the oxidative stresses associated with myriad biotic and abiotic challenges and inherent to photosynthesis").

I found that it was pedagogic and lively to illustrate how, if a constraint is removed on an organism, future generations will be able to get rid of the machinery, partially or totally (from the OMIM article on Hypoascorbemia:)

The mechanism whereby an organism loses a particular metabolic function which is of no use in a particular environment was discussed by King and Jukes (1969). The accumulation of random mutations in the gene for the relevant enzyme might be expected to destroy the functional capacity of the enzyme, most mutations being disruptive.

It is, IMO, relevant here; the same logic applies to the loss of Vit C synthesis in higher primates, according to the OMIM, except that it is a matter of offer (more provided exogenously), for the latter, and of demand, for the former (more demanded because of the environment challenges)-- I thus created cross-references in the text in the hope of making it more lively, in accordance with CZ recommendations.

Pierre-Alain Gouanvic 20:04, 6 January 2008 (CST)

Hi Pierre. Mechanisms of natural selection require very many generations before even beneficial mutations will become fixed in a population (about 300 for a single mutation); here you're talking about at best a neutral mutation. Cultivated plants though have been subject to artificial selection, and it is by comparison easy to see how this can result in the los of even beneficial alleles. So the loss of vitamin C is very unlikely to be the consequence of natural processes, but is plausibly accounted for (if true) as a by product of artificial selection.Gareth Leng 03:25, 7 January 2008 (CST)

Thank you for this detailed explanation, I applaud your patience...

I will try to find in the literature the link (if any) between

1. "Domestication of plants (...) is an artificial selection process (...) to produce plants that have fewer undesirable traits of wild plants, and which renders them dependent on artificial (usually enhanced) environments for their continued existence." (From the CZ article http://en.citizendium.org/wiki/Plant_breeding#Domestication)
2. "Plants produce large amounts of L-ascorbic acid to facilitate resistance to the oxidative stresses associated with myriad biotic and abiotic challenges and inherent to photosynthesis" (cf supra)

If I come up with something, I'll submit it. I think I have a hint :

"One important difference between wild and cultivated fruits is that sugar in the pulp of wild fruits tends to be hexose-dominated (some fructose and considerable glucose) while that of cultivated fruits tends to be highest in sucrose, a disaccharide." Milton K (1999). "Nutritional characteristics of wild primate foods: do the diets of our closest living relatives have lessons for us?". Nutrition 15: 488–98. PMID

(VC, formerly known as hexuronic acid, is a sugar derivative. Do differences in carbohydrate composition condition vitamin C composition?)

In any case, the most important for this article is that tropical forests are where exceptional intakes of VC are possible, and where, as a result, the VC synthecizing enzyme GULO could be lost (as suggested by OMIM (McKusick), Pauling, Stone), and the migration out of this habitat is explanatory of most of this drastic decline in VC intake. This is the basis of the 60 years-old debate on VC requirements -- that we must cover, IMO.

But do you think it is appropriate for this article to explore the relationship between the "weakness" of cultivated fruits and their vitamin C content?

Pierre-Alain Gouanvic 08:54, 7 January 2008 (CST)

Issues with some VC content estimates

Cf Comparison of ascorbic acid content of Emblica officinalis fruits determined by different analytical methods Pierre-Alain Gouanvic 01:15, 26 February 2008 (CST)

Side effects and contraindications / Side effects and contraindications / Rebound scurvy citation needed

Side effects and contraindications

moving stuff around

looks good to me Hayford Peirce 03:11, 29 January 2009 (UTC)

Subpage for therapeutic uses?

Article is getting long yet I would like to add to therapeutic uses section. Can we make a subpage Vitamin C/Medical uses or some similar name? - Robert Badgett 03:14, 29 January 2009 (UTC)
  1. Barja, Gustavo. (1996) Ascorbic Acid and Aging. in Harris, James W. (1996). Ascorbic acid: biochemistry and biomedical cell biology. New York: Plenum Press. ISBN 0-306-45148-4.