Vitamin C

:This article is about the nutrient.

Reported potential harmful effects

Reports of harmful effects of vitamin C tend to receive great prominence in the world's media. Many such reports have never been published in peer reviewed journals, which casts some suspicion on their credibility.

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• In April 1998 the journal 'Nature' reported alleged carcinogenic and teratogenic effects of excessive doses of vitamin C. The effects were noted in test tube experiments and on only two of the 20 markers of free radical damage to DNA. They have not been supported by further evidence from living organisms.
• University of Southern California researchers in April 2000, reported a thickening of the arteries of the neck in persons taking high vitamin C doses. It was later pointed out by vitamin C advocates that this can be explained by vitamin C's collagen synthesising role leading to thicker and stronger artery walls.
• In June 2004, Duke University researchers reported an increased susceptibility to osteo-arthritis in guinea pigs fed a diet high in vitamin C. However, a 2003 study at Umeå University in Sweden, found that "the plasma levels of vitamin C, retinol and uric acid were inversely correlated to variables related to rheumatoid arthritis disease activity."
• "Rebound scurvy" is an often quoted theoretical, and never observed, condition that occurs when the amount of daily intake of Vitamin C is rapidly reduced from a very large amount to a relatively lower amount. This is an exaggeration of the rebound effect that occurs because ascorbate-dependent enzyme reactions continue for 24-48 hours, and use up vitamin C in the blood that is not being replenished. The effect is to lower one's serum vitamin C blood concentration to less than normal for a short amount of time. During this period of time there is a slight risk of cold or flu infection through reduced resistance. Within a couple of days the enzyme reactions shut down and blood serum returns to the normal level of someone not taking high supplements. This is not scurvy, which takes weeks of zero vitamin c consumption to produce symptoms. It is something people who take large vitamin C supplements need to be aware of in order to manage phased rather than sudden changes to the amount taken.
• Kidney stones are a much cited harmful side effect of taking vitamin C in larger than normal amounts. However research has shown this not to be the case ³