Are Recommended Daily Allowances for Vitamin C Adequate?

Pauling, Linus

doi:10.1073/pnas.71.11.4442

Cited by 49 publications

(25 citation statements)

References 33 publications

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“…The nutritional recommendation for vitamin C, 60 mg/day [27], is not based on clinical or epidemiological studies suggesting that such a dose would be the best for health in the long term; rather, the only criterion is that such a dose prevents overt scurvy with an ample safety margin [11,[27][28][29][30][31][32][33]. Vitamin C participates in a number of enzymatic and nonenzymatic reactions [20,[32][33][34][35], and consequently it is quite possible that the physiological effects of the vitamin are not limited to the prevention of overt scurvy.…”

Section: Discussionmentioning

confidence: 99%

Vitamin C, the placebo effect, and the common cold: A case study of how preconceptions influence the analysis of results

Hemilä

1996

Journal of Clinical Epidemiology

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A large number of placebo-controlled studies have shown that vitamin C supplementation alleviates the symptoms of the common cold, but widespread skepticism that vitamin C could have any significant effect remains. One of the most influential common cold studies, published in 1975, was carried out by Thomas Karlowski et al. at the National Institutes of Health. Their placebo consisted of lactose, which can easily be distinguished from ascorbic acid by taste. Karlowski et al. found a 17% decrease in the duration of cold episodes in the group administered vitamin C (6 g/day); however, they suggested that the decrease was entirely due to the placebo effect. In this article it will be shown that the placebo effect is not a valid explanation for the results of the Karlowski study, as it is inconsistent with their results. This is an important conclusion for two reasons. First, the placebo explanation becomes even more unreasonable as regards the reported benefits found in several other studies with valid placebo tablets. Second, as the results from the Karlowski study are not due to the placebo effect, their results can be used to assess the quantitative effects of vitamin C supplementation. The most important conclusions from Karlowski's study are that therapeutic vitamin C supplementation during a common cold episode appears to be as effective as regular supplementation, and that there appears to be linear dose dependency at least up to 6 g/day. These findings suggest that large therapeutic vitamin C doses might alleviate the symptoms of the common cold substantially.

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Section: Discussionmentioning

confidence: 99%

Vitamin C, the placebo effect, and the common cold: A case study of how preconceptions influence the analysis of results

Hemilä

1996

Journal of Clinical Epidemiology

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“…The goal of nutritional recommendations is to prevent overt scurvy and for that purpose the recommendation of 30-60 mg/day provides a good margin of safety. However, these recommendations are not based either on clinical or epidemiological studies suggesting that 30 or 60 mg/day is an optimal dose for human beings in the long term, or on biochemical studies suggesting that such doses would saturate the numerous vitamin C dependent reactions (7,11,14,15,20,24,29,33). The studies analyzed in this paper suggest that there may be groups of people who benefit from doses larger than those officially recommended.…”

Section: Discussionmentioning

confidence: 91%

Vitamin C and Common Cold Incidence: A Review of Studies with Subjects Under Heavy Physical Stress

Hemilä¹

1996

Int J Sports Med

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Several studies have observed an increased risk of respiratory infections in subjects doing heavy physical exercise. Vitamin C has been shown to affect some parts of the immune system, and accordingly it seems biologically conceivable that it could have effects on the increased incidence of respiratory infections caused by heavy physical stress. In this report the results of three placebo-controlled studies that have examined the effect of vitamin C supplementation on common cold incidence in subjects under acute physical stress are analyzed. In one study the subjects were school-children at a skiing camp in the Swiss Alps, in another they were military troops training in Northern Canada, and in the third they were participants in a 90 km running race. In each of the three studies a considerable reduction in common cold incidence in the group supplemented with vitamin C (0.6-1.0 g/day) was found. The pooled rate ratio (RR) of common cold infections in the studies was 0.50 (95 % CI: 0.35-0.69) in favour of vitamin C groups. Accordingly, the results of the three studies suggest that vitamin C supplementation may be beneficial for some of the subjects doing heavy exercise who have problems with frequent upper respiratory infections. IntroductionSeveral studies have suggested that there is an increased risk of respiratory infections in subjects doing heavy exercise (9,12,17,21,25,30). It is not well known what the physiological basis of this increased susceptibility is (9,17), but decrease in the proliferative responses of T-lymphocytes (8,9,13,17), depression of the immune system by corticosteroids produced under physical stress (9,17), or harm done to the immune system cells by oxygen radicals generated during heavy exercise (41) are among the possible explanations.Vitamin C has been reported to increase the proliferative responses in T-lymphocytes (2,18,23,26,38), to prevent the defects in neutrophils caused by corticosteroids (5,27,36), and it is also a major biological antioxidant (15). Thus vitamin C possibly could aid the immune system in subjects under heavy physical stress. It is also noteworthy that the highest concentrations of vitamin C in the body are found in the adrenal glands and adrenal vitamin C is rapidly depleted by various forms of stress (20); however, the role of vitamin C in the adrenal glands is not well understood. Moreover, in several laboratory animals vitamin C has increased resistance to low temperature (6,39), further suggesting some role for the vitamin in stress responses.Placebo-controlled studies have shown that vitamin C ( 1 g/day) decreases the severity of common cold episodes (15,16). In contrast, vitamin C has not consistently affected the common cold incidence, although a few studies have reported a significant decrease (15,16,28). The largest studies have not found any marked effect on the incidence of colds (3,15,16,22,32). Nevertheless, it is possible that vitamin C affects common cold incidence in certain limited groups of people. The purpose of the present work wa...

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“…For example, they have been disregarded in the recommended dietary allowances monograph on nutritional recommendations (20), which is concerned only with the prevention of overt scurvy (41,44,45,(62)(63)(64)(65)(66)(67)(68)(69). It is noteworthy and quite surprising that in this influential monograph, Chalmers' review (23) and Dykes and Meier's review (24) are used as the basis for claiming that vitamin C has no proven effects on the common cold (20), although some of the notable shortcomings of both reviews should have been apparent to anyone familiar with the original publications.…”

Section: Open Questionsmentioning

confidence: 99%

Vitamin C supplementation and common cold symptoms: Problems with inaccurate reviews

Hemilä

1996

Nutrition

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In 1971, Linus Pauling carried out a meta-analysis of four placebo-controlled trials and concluded that it was highly unlikely that the decrease in the "integrated morbidity of the common cold" in vitamin C groups was caused by chance alone (P < 0.00003). Studies carried out since then have consistently found that vitamin C ( 1 g/d) alleviates common cold symptoms, indicating that the vitamin does indeed have physiologic effects on colds. However, widespread conviction that the vitamin has no proven effects on the common cold still remains. Three of the most influential reviews drawing this conclusion are considered in the present article. Two of them are cited in the current edition of the RDA nutritional recommendations as evidence that vitamin C is ineffective against colds. In this article, these three reviews are shown to contain serious inaccuracies and shortcomings, making them unreliable sources on the topic. The second purpose is to suggest possible conceptual reasons for the persistent resistance to the notion that vitamin C might have effects on colds. Although placebo-controlled trials have shown that vitamin C does alleviate common cold symptoms, important questions still remain.

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Are Recommended Daily Allowances for Vitamin C Adequate?

Cited by 49 publications

References 33 publications

Vitamin C, the placebo effect, and the common cold: A case study of how preconceptions influence the analysis of results

Vitamin C, the placebo effect, and the common cold: A case study of how preconceptions influence the analysis of results

Vitamin C and Common Cold Incidence: A Review of Studies with Subjects Under Heavy Physical Stress

Vitamin C supplementation and common cold symptoms: Problems with inaccurate reviews

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