May 30, 2019

Vitamin C in human disease

As an electron donor, vitamin C could be involved in several disease processes. Vitamin C is present in almost all foods of plant origin. The minimal vitamin C requirement for humans is defined as 40–60 mg/day to combat dietary deficiency [28]. However, vitamin C status decreases with both age and smoking, and is associated with chronic diseases such as rheumatoid arthritis and cancer [28]. Vitamin C might be consumed by preventing free radical-induced damage of DNA, which is thought to be an initiating step in cancer formation. The possible use of vitamin C in cancer therapy and prevention has been an area of great interest. Vitamin C supplements, which are able to prevent the formation and/or promote the repair of pre-mutagenic oxidative DNA lesions, are suggested to be of use in cancer prevention. Recently, a report showed that daily supplementation with vitamin C at high doses increased the survival time of terminal cancer patients, suggesting that vitamin C can have important anticancer properties. Indeed, vitamin C is proved to kill or inhibit the growth of many tumor cell lines [28]. Regarding cancer prevention, several epidemiological studies have linked the consumption of a diet rich in fruit and vegetables with lower incidence of many types of cancer [3, 2934]. The hypothesis supports oxidative processes regulate ascorbate catabolism in humans, although direct proof is currently lacking. Ascorbate plays an important role as a first defense against oxidative stress. Smokers present one example of the relationship between oxidants and ascorbate since they expose themselves to oxidants via inhaled smoke. These oxidants have been demonstrated to induce lipid peroxidation in vitro, which is prevented by the presence of ascorbate. It is demonstrated that the turnover of 14C-labeled ascorbate has been 40% greater in smokers compared with nonsmokers. Ascorbate requirements of smokers based on intake and serum concentrations show that smokers may require as much as three times the dose of ascorbate than nonsmokers to avoid risk of efficiency[3032, 34].

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