Increased doses of vitamin E may produce positive results for heart
health, says a new study from the US that questions the ‘under-dosing’
used in earlier clinical trials. The study, published early online in
Free Radical Biology and Medicine, reports that a higher dose – 3200
International Units – of vitamin E is needed to reduce oxidative stress
in individuals at risk for cardiovascular disease, and this may be why
previous trials using lower doses failed to show any benefits for the
vitamin. By focussing on the ability of vitamin E (RRR-alpha-tocopherol)
to reduce levels of F2-isoprostanes, a biomarker of free
radical-mediated lipid peroxidation, the researchers found that higher
doses of the vitamin were needed to counteract oxidative stress in
people with high cholesterol levels and enhanced oxidative stress. There
are eight forms of vitamin E: four tocopherols (alpha, beta, gamma,
delta) and four tocotrienols (alpha, beta, gamma, delta).
Alpha-tocopherol (alpha-Toc) is the main source found in supplements and
in the European diet, while gamma-tocopherol (gamma-Toc) is the most
common form in the American diet. Roberts and co-workers recruited eight
participants (average age 34, seven women) for a time-course study and
assigned them to receive 3200 IU of RRR-alpha-tocopherol for 20 weeks.
They report that 16 weeks of supplementation was needed to achieve
maximum suppression of plasma F2-isoprostane concentrations. A
double-blind randomized placebo-controlled study was performed with 35
volunteers (average age 42, 23 women) to investigate the effects of
different doses on plasma F2-isoprostanes concentrations. The volunteers
were placebo or 100, 200, 400, 800, 1600, or 3200 IU of vitamin E daily
for 16 weeks The researchers report a dose-dependent effect of vitamin E
on the percentage reduction in plasma F2-isoprostane concentrations.
Statistical significance of the reduction was achieved with the higher
doses, with 1600 IU reducing F2-isoprostane levels by 35 per cent, and
3200 IU of the vitamin producing a 49 per cent reduction. «The results
of this study should provide a framework for future studies assessing
the ability of therapeutic agents to suppress oxidant stress in humans,»
wrote the authors.