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Research Newsletter-Spring/Summer 2010

DO "ANTIOXIDANTS PREVENT HEALTH-PROMOTING EFFECTS OF PHYSICAL EXERCISE IN HUMANS"?



Scott W. Leonard, LPI Senior Research Assistant


A paper published in 2009 by Ristow et al. in the Proceedings of the National Academy of Sciences, "Antioxidants Prevent Health-Promoting Effects of Physical Exercise in Humans", cast doubt on the combined health benefits of antioxidant consumption and exercise. While the data do not appear to be flawed and are important, we believe the authors have overstated their findings.

There is no doubt that achieving and maintaining a healthful weight is a benefit of exercise, but the molecular mechanisms underlying this effect are unclear. Ristow proposed that reactive oxygen species (ROS) have an essential role in promoting insulin sensitivity during exercise, one of the known benefits of exercise. They then claimed that antioxidant use, leading to a decrease in ROS, is detrimental to the health-promoting effects of exercise. There are many good studies, including several from our labs, showing benefits of antioxidant use during exercise in decreasing markers of oxidative stress. Antioxidants have 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 proposed to be related to oxidative stress. Ristow 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 antioxidant proteins like superoxide dismutase and glutathione-synthesizing enzymes.

The study's authors focused 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 during exercise in diabetics, who were excluded from the study. The authors tried to link their findings to the molecular changes that occur in type 2 diabetics, but their choice of healthy men instead of diabetics made that problematic. It is well accepted that there are health benefits from exercise and antioxidant consumption, whether from the diet or supplementation, alone or in combination. Indeed, a diet rich in fruits and vegetables and regular exercise have long been recognized to decrease the risk for many chronic diseases.

The statement by Ristow that "fruits and vegetables may exert health-promoting effects despite their antioxidant content" seems particularly inappropriate. Humans depend on fruits and vegetables and other dietary sources for the important physiological antioxidants, vitamins C and E. In a recent commentary on 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".

Last updated June 2010