High intensity exercise can bring on oxidative stress, where free radicals attack tissue and increase ageing. Oxidative stress has been linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease.
The researchers, from San Antonio Catholic University in Spain, showed that a drink containing black grape, raspberry and red currant concentrates reduced protein oxidation by 23 per cent. Similar tests for a placebo crossover showed protein oxidation increased by 12 per cent.
The controlled experiment measured blood markers or oxidative stress: followed the effects of oxidative stress for thirty sportsmen before and after high intensity exercise.
The concentration of some markers was not affected by the antioxidant supplements, while levels of creatine kinase (CK) and lipid oxidation (TBARS) was less in the supplemented test than placebo.
"The results observed in the decrease of the levels of carbonyl groups (as markers of protein oxidation in the cyclists when they consume the polyphenol drink, indicate a decrease in the oxidative damage induced by physical activity in spite of the total antioxidant state in the plasma remaining the same," wrote the researchers in Clinical Nutrition (published on-line 19 January 2006, doi: 10.1016/j.clnu.2005.11.007).
The antioxidant drink was supplied by Hero-Spain and contained black grape, raspberry and red currant concentrates. Vitamin C (20 mg per litre) was contained in both the drink and the placebo.
"The antioxidant effect of the beverage could be due to polyphenolic content and not to the vitamin C due to the fact that the placebo contains the same quantity of vitamin C," said the researchers.
Exercise induced oxidative stress is only seen after high intensity or long duration exercise. A 1987 study from the University of Alberta showed that moderate exercise did not affect oxidative stress, and that low intensity exercise actually protected against it.
While oxidative stress does not seem to affect short-term performance, it is not known whether there are any long-term health consequences of EIOS.
The results will be welcomed by a sports drink industry that continues to grow. Mintel reports that the US sports drink market produced $2.9 billion (€2,400 million) in sales in 2004, with Gatorade dominating with 82 per cent of the market. Sales are predicted to grow to $3.1 billion (€ 2600 million) by 2009.
In the UK, the sports drink market is growing even faster with a 180 per cent increase since 2000. The market was estimated to be worth £207 million (€302 million) in 2005. GlaxoSmithKline's Lucozade sport holds 42 per cent of the market, while Gatorade and Powerade are steadily increasing their presence and share.