Epidemiology of Vitamin C

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A review is presented of the epidemiology of vitamin C. This review summarizes the epidemiologic relationship of vitamin C intake to mortality from all causes, cancer, and cardiovascular diseases and the results of randomized controlled trials involving vitamin C supplements and mortality. Many studies show an inverse relationship between mortality and vitamin C intake, particularly for levels close to the current U.S. recommended dietary allowance (RDA) of 75-90. mg per day for adults. The inverse relationship is particularly strong for serum vitamin C. However, several studies show no relationship at all or no significant relationship after controlling for confounding variables. There is little evidence of a relationship at high or low levels of vitamin C supplement intake. The results of randomized intervention trials assessing the impact of supplemental vitamin C on mortality and cancer survival are largely negative, but there are selective instances of benefits. There have been very few intervention trials focusing on vitamin C. Most of the available prospective cohort data on vitamin C and mortality have not been analyzed. Additional cohort analyses and new intervention trials would substantially refine the evidence. Vitamin C is an essential human nutrient and there is substantial epidemiologic evidence that regular intake of at least the RDA of vitamin C is beneficial for optimum health.

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... [11][12] Vitamin C (ascorbic acid) is an important antioxidant in the body and has been used to prevent and treat various diseases. [13][14][15] It has been suggested that vitamin C deficiency causes immunosuppression, and may boost the immune system and act as an anti-inflammatory agent by inhibiting cytokine secretion. 16 However, the effects of vitamin C supplementation on rhinitis symptoms in allergic rhinitis patients are still controversial. ...
Introduction: Exercise training and vitamin C supplementation have both been recommended as an effective adjuvant treatment in the management of symptoms in patients with many diseases. However, its effects on rhinitis symptoms remain unclear. The aim of the present study was to determine the effects of exercise training alone, and in combination with vitamin C supplementation, on rhinitis symptoms in allergic rhinitis patients. Methods: Twenty-seven rhinitis patients were randomized into 3 groups: control (CON; n = 8), exercise (EX; n = 9), and exercise combined with vitamin C (EX + Vit.C; n = 10). The exercise training protocol consisted of walking and/or running on a treadmill at 65-70% heart rate reserve for 30 min per session, 3 times per week for 8 weeks. The EX + Vit.C group ingested 2,000 mg vitamin C per day. Results: After 8 weeks, both EX and EX + Vit.C groups increased peak aerobic capacity and peak nasal inspiratory flow (PNIF) and exhibited significantly decreased rhinitis symptoms, nasal blood flow (NBF) and malondialdehylde levels compared to pre-test. Rhinitis symptoms and NBF after nasal challenge with house dust mite decreased significantly in the EX and EX + Vit.C groups. The EX and EX + Vit.C groups had significantly lower nasal secretion interleukin (IL)-4, but higher nasal secretion IL-2 levels, than the CON group. Conclusions: This study clearly confirms that aerobic exercise training significantly improved clinical of allergic rhinitis and cytokine profiles. Nonetheless, with the limited power of small sample size, whether adding vitamin C is any beneficial is not shown. A larger randomized controlled trial is thus warranted.
This report reviews published epidemiologic research on the associations of vitamin and mineral supplementation with cancer risk. Although the literature on nutrition and cancer is vast, few reports to date have addressed supplemental nutrients directly (seven clinical trials, 16 cohort, and 36 case-control studies). These studies offer insight into effects of nutrients that are distinguishable from effects of other biologically active compounds in foods. Randomized clinical trials have not shown significant protective effects of beta-carotene, but have found protective effects of: alpha-tocopherol against prostate cancer; mixtures of retinol/zinc and beta-carotene/alpha-tocopherol/selenium against stomach cancer; and selenium against total, lung, and prostate cancers. Cohort studies provide little evidence that vitamin supplements are associated with cancer. Case-control studies have reported an inverse association between bladder cancer and vitamin C; oral/pharyngeal cancer and several supplemental vitamins; and several cancers and vitamin E. A randomized clinical trial, a cohort study, and a case-control study have all found inverse associations between colon cancer and vitamin E. Overall, there is modest evidence for protective effects of nutrients from supplements against several cancers. Future studies of supplement use and cancer appear warranted; however, methodologic problems that impair ability to assess supplement use and statistical modeling of the relation between cancer risk and supplement use need attention.