PROTECTIVE ROLE OF DIETARY VITAMIN-E ON OXIDATIVE STRESS IN AGING

Free radical reactions and the peroxidation of membrane lipids have been implicated in the mechanism of aging and age-associated degenerative conditions. Vitamin E appears to play a critical role in protecting the cell membrane from free radical reactions and peroxidation of polyunsaturated fatty acids (PUFA). In a series of human studies, the protective role of vitamin E supplementation against oxidative stress was investigated in young and older volunteers. Muscle biopsies taken from young (<30 y) men, following an eccentric exercise bout, exhibited a decreased level of vitamin E and increased conjugated diene status, an indication of lipid peroxidation. Older men (>55 y) supplemented with vitamin E for 48 d excreted a lower level of lipid peroxidation products in urine compared to placebo control following eccentric exercise. In conditions where the composition of membrane fatty acids changes to more PUFA, older subjects may be at a greater risk of oxidative damage. In a study of 15 young (<35 y) and 10 older (>51 y) women receiving fish oil capsules for 3 months, older women showed a greater increase in plasma levels of eicosapentaenoic (EPA) (p<0.001) and docosahexaenoic (DHA) (p<0.5) acids compared to young subjects. By substituting membrane fatty acids with potentially unstable (n-3) fatty acids of fish oil, older subjects were found to be at a greater risk of oxidative stress than young subjects. This was indicated by decreased E/EPA+DHA (4.9 fold in older and 3.6 fold in young women) and a higher increase (p<0.05) in lipid peroxides (63.1% in older vs. 29.4% in young women) in their plasma. These findings indicate that vitamin E plays an important protective antioxidant role in older subjects, particularly in conditions where oxidative stress and free radicals are potentiated.