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Do "Antioxidants Prevent Health-Promoting Effects of Physical Exercise in Humans"?


A recently published manuscript by Ristow et al., "Antioxidants prevent health-promoting effects of physical exercise in humans" (Proc Natl Acad Sci USA 2009 May 26;106(21):8665-70), has cast some doubt on the combined health benefits of antioxidant consumption and exercise. While the data do not appear to be flawed and are of importance, we believe the authors have overstated their findings. First of all, the health-promoting benefits of exercise or antioxidants are still ambiguous.

There is no debate that achieving a healthy weight is a benefit of exercise, but the molecular mechanisms underlying this effect are unclear. In the study by Ristow et al., reactive oxygen species (ROS) are proposed to have an essential role in promoting insulin sensitivity during exercise, one of the known benefits of exercise, and a decrease in ROS from antioxidant use is discussed as detrimental to the health-promoting effects of exercise. There are many good studies showing benefits of antioxidant use during exercise on decreasing markers of oxidative stress and aging. Antioxidant use has been shown to decrease DNA damage, lipid peroxidation, and protein oxidation following exercise. The combination of antioxidants and exercise has also been shown to delay brain aging, a phenomenon also proposed to be related to oxidative stress. Ristow et al. reported that antioxidant supplementation blocked the induction of antioxidant enzymes in the body. However, the supplemental antioxidants may have negated the need for up-regulation of endogenous antioxidants.

The authors focus on changes in insulin sensitivity, but it is known that contracting skeletal muscle can take up glucose independently of insulin during exercise, and glucose uptake is normal in diabetics during exercise, who were excluded from the study. The authors try to make the link between their findings and the molecular changes that occur in type 2 diabetics, but their choice of healthy men instead of diabetics makes this problematic. It is well accepted that there are health benefits from exercise and antioxidant consumption, whether from diet or supplementation, alone or in combination. Indeed, a diet rich in fruits and vegetables has been recognized for some time to decrease the risk of chronic diseases.

The recent publication that states antioxidants prevent the health-promoting effects of physical exercise is clearly overstating the findings. Their statement that "fruits and vegetables may exert health-promoting effects despite their antioxidant content" seems particularly inappropriate. In a recent commentary on the change in the oxidative stress paradigm discussed at the third international symposium on "Nutrition, oxygen biology and medicine-micronutrients, exercise, energy and aging disorders" in Paris, Dr. Regina Brigelius-Flohé commented that "it remained obvious that a lot of work is needed to fully understand the conditions and individual situations under which ROS are beneficial or detrimental" (Genes Nutr 2009 Sep;4(3):161-3, Commentary: oxidative stress reconsidered. Brigelius-Flohé R.).