vitamin e

Far from protecting athletes from oxidative stress and impaired immunity, supplementation with vitamin E may actually make matters worse, according to an important new study of people taking part in the 2002 Triathlon World Championships held in Kona, Hawaii.

Intensive and sustained exercise is known to create an imbalance between damaging reactive oxygen species (free radicals) and the body’s antioxidants which protect against them, leading to the condition of oxidative stress that can be measured in various ways, including levels of lipid peroxidation.

Vitamin E functions primarily as an antioxidant preventing the propagation of lipid peroxidation. It also plays an important role in the maintenance of immune function. So it is natural to assume that vitamin E supplements would reduce oxidative stress and immunosuppression during heavy exertion.

This was the hypothesis the US research team put to the test with the Kona triathletes, who were due to complete a 3.9k ocean swim, 180k bike race and 42k run. Thirty-eight triathletes received either vitamin E (800IU daily) or placebo capsules in a randomised double-blind fashion for two months before the event, with blood, urine and saliva samples collected the day before the race, 5-10 minutes post-race and 1.5 hours post-race.

Key findings were as follows:

• Race times did not differ between the groups, with both groups maintaining an intensity of about 80% maximum heart rate during the bike and run portions;
• Blood levels of α-tocopherol (the form in which vitamin E is maintained in human plasma) were approximately 75% higher in the vitamin E group pre- and post-race;
• While most measures of oxidative stress were similar in both groups, some were markedly higher in the vitamin E group.

How can this be explained? The researchers point to increasing evidence that, depending on the dose and experimental conditions, vitamin E can exert antioxidant, neutral or pro-antioxidant effects.

‘High doses of α-tocopherol combined with high oxidative stress may create α-tocopherol radicals that may initiate processes of lipid peroxidation by themselves.’

When antioxidant networks are balanced, this pro-oxidant action of vitamin E radicals is inhibited by co-antioxidants such as vitamin C. The athletes in the current study avoided vitamin C supplementation, and their normal dietary vitamin C intake may have been insufficient to inhibit vitamin E pro-oxidant effects, given the high doses consumed.

Concluding that there is no case for vitamin E supplementation alone before an ultraendurance event, the researchers call for further research on the potential effects of frequent large-dose vitamin E supplementation on the long-term health status of ultra-athletes.

Med Sci Sports Exerc, vol 36, no 8, 1328-1335, 2004-12-22