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• What causes Vitamin C deficiencies? • Is it possible to overdose on Vitamin C? • The effect of a Vitamin C overdose on Copper • The effect of a Vitamin C overdose on Zinc • The effect of a Vitamin C overdose on Manganese • The effect of a Vitamin C overdose on Calcium • The effect of a high dose of Vitamin C on Nickel & Vitamin E • Optimal supplementation of Vitamin C by population average • How much Vitamin C should one supplement? • Vitamin C supplementation during Pregnancy and Nursing • The discovery and history of ascorbic acid • 2014 RDA or DRI (Dietary Reference Intake) without naturally occurring cofactors - such as rutin and hesperidin - were used), and that epidemiological data showed no evidence at all that higher dosages of ascorbic acid caused cancer. (listed below) that cause a Vitamin C deficiency or reduce its benefits. amount, or specific Vitamin C side effects that apply to everyone.
Criteria for inclusion were placebo-controlled trials to prevent or treat the common cold using oral doses of vitamin C of 200 mg/day or more. Literature from 1940 to 2004 was methodically screened. Vitamin C was identified in the 1930s by Albert Szent-Györgyi, who received his Nobel Prize partly for this work. He found that paprika is a particularly rich source of the vitamin, which made it possible to produce kilograms of it for research purposes ([1963] Annu Rev Biochem 32: 1–14). Nowadays, the most convenient way to increase vitamin C intake is by way of 500-mg tablets, but further research is needed to explore the conditions in which supplementation may be beneficial. /10.1371/journal.pmed.0020168.g001An overview of the results of the three meta-analyses is shown in Table 1. Incidence was not altered in the subgroup of 23 community studies where prophylactic doses as high as 2 g daily were used. But a subgroup of six studies of marathon runners, skiers, and soldiers exposed to significant cold and/or physical stress experienced, on average, 50% reduction in common cold incidence.
/10.1371/journal.pmed.0020168.t001Duration of cold episodes that occurred during prophylaxis was significantly reduced in both children and adults. For children this represented an average reduction of 14% in symptom days, while in adults the reduction was 8%. For the seven trials that evaluated the therapeutic impact of vitamin C used at the onset of symptoms (all in adults), benefits were not observed for duration of episodes, although one of the large trials recorded a statistically significant reduction in the duration of colds among participants administered a single vitamin C dose of 8 g on the day of symptom onset [3]. Implications of the ReviewThe lack of effect of prophylactic vitamin C supplementation on the incidence of common cold in normal populations throws doubt on the utility of this wide practice. The clinical significance of the minor reduction in duration of common cold episodes experienced during prophylaxis is questionable, although the consistency of these findings points to a genuine biological effect.
In special circumstances, where people used prophylaxis prior to extreme physical exertion and/or exposure to significant cold stress, the collective evidence indicates that vitamin C supplementation may have a considerable beneficial effect; it was the results of one of these six trials, with schoolchildren in a skiing school [4], that particularly impressed Pauling [1]. However, great caution should be exercised in generalizing from this finding, which is based mainly on marathon runners. No benefits have been observed from therapeutic use of doses totalling 10 g that was divided for the first three days of illness. The equivocal findings of the large study, which used 8 g only on the day of onset of respiratory symptoms [3], are tantalising and deserve further assessment. None of the therapeutic trials carried out so far has examined the effect of vitamin C on children, even though the prophylaxis trials have shown substantially greater effect on episode duration in children.