Renal Transplantation

Despite major advances in the management of patients with end-stage renal disease, these individuals still have a threefold higher risk of dying from ischemic heart disease (IHD) compared with age-matched healthy subjects.79 Established risk factors for IHD, such as hyperlipidemia and hypertension, remain after transplantation, and there is evidence of increased oxidative stress and enhanced low density lipoprotein oxidation in renal allograft recipients.80,81 Recent studies have also shown impaired endothelium-dependent vasodilation in patients with renal allografts independent of hypercholesterolemia, hypertension, uremia, or treatment with cyclosporine.82,83 All the above factors appear to impair endothelial function in part by increasing vascular production of superoxide anions, which may inhibit the release of nitric oxide or inactivate it directly.84,85 Vitamin C in renal transplant recipients has been shown to improve flow mediated, endothelium-dependent vasodilation and increase the resistance of lipoproteins in dilute serum to oxidation.86

Age-Related Eye Diseases

Degenerative eye disorders are common among the elderly. There is evidence vitamin C can reduce oxidative stress and lower the risk of such age-related degenerative changes.87,88

A prospective study in health professionals showed lower rates of selfreported cataracts among those who took multivitamin supplements or who were long-term users of vitamin C.89 Another study found the 5-year risk for cataracts was 60% lower among persons who, at follow-up, reported the use of multivitamins containing vitamin C or E for more than 10 years compared to nonusers.90

Alzheimer’s Disease

There is evidence in patients with Alzheimer’s disease (AD) that there is increased sensitivity of the cerebral cortex to free radicals, perhaps related to lower activity of antioxidant enzymes such as superoxide dismutase.91,92 The major targets for oxidation in the brain are lipids and lipoproteins.

Supplementation with vitamin E and C significantly increases the concentrations of both vitamins in plasma and CSF and significantly decreases the in vitro oxidation of plasma lipoproteins.93 In contrast, supplementation with vitamin E alone did not decrease lipoprotein oxidation. Two recent studies found patients with AD have low plasma vitamin C concentrations despite an adequate diet and supplementation with vitamin C may lower the risk of AD.94,95

Vitamin C and Viral Infections

The Common Cold

The role of vitamin C in the prevention and treatment of the common cold remains controversial. A review of controlled studies suggests a reduction of at least 80% in the incidence of pneumonia in vitamin C groups and substantial treatment benefit from vitamin C in elderly patients hospitalized with pneumonia or bronchitis.96,97 It seems the preventive effects of supplementation are mainly limited to subjects with low dietary vitamin C intake, but therapeutic effects may occur in wider population groups.96 Research has shown long-term daily supplementation with large doses (1 g daily during winter months) of vitamin C does not appear to prevent colds, but there may be a modest benefit in reducing the duration of cold symptoms.98,99