Vitamin E ingestion does not improve arterial endothelial dysfunction in older adults

Abstract

Endothelial dysfunction is thought to be an important early event in atherogenesis, related in part to reduced bioavailability of nitric oxide in the arterial wall. Endothelial function may be impaired in the presence of oxidised low density lipoprotein. The use of vitamin E as an anti-oxidant might enhance the bioavailability of nitric oxide in this situation. The effect of vitamin E 1000 IU/day on arterial endothelial physiology was studied in 20 asymptomatic older subjects, aged 45-70 years, who showed evidence of age-related endothelial dysfunction. Endothelial function was assessed non-invasively using brachial ultrasound and the primary outcome measure was flow-mediated endothelium-dependent dilatation (FMD) in response to reactive hyperaemia. A double-blind, placebo-controlled, randomised crossover design was employed. After 3 weeks of stabilisation on a standard fat-reduced diet, subjects received vitamin E or placebo for 10 weeks in random order, separated by a washout period of 8 weeks. There were no significant changes in blood pressure, plasma lipid or lipoprotein concentrations. Plasma alpha-tocopherol increased from 50+/-3 (mean+/-S.E.M.) to 91+/-6 micromol/l (P < 0.001) with vitamin E ingestion. Total plasma F2alpha-isoprostanes, a measure of free radical-induced lipid peroxidation, were not altered by vitamin E ingestion (0.86+/-0.26 versus 0.82+/-0.25 nmol/l, P > 0.6). FMD was not significantly different between the placebo and vitamin E periods (2.7+/-0.6% versus 2.4+/-0.4%). Variation in FMD was not correlated with change in plasma alpha-tocopherol (r = - 0.03, P > 0.8). The study was powered to detect a minimum change in FMD of 2%. Glyceryl trinitrate endothelium-independent dilatation was not significantly changed with vitamin E (13.7+/-1.3% versus 13.6+/-1.4%,). These results exclude a major impact of medium-term supplementation with vitamin E on arterial endothelial function when age-related dysfunction is already present.