Exercise is accepted to have many benefits to health, promoting fitness and weight loss whilst also improving diseases such as diabetes and related insulin resistance. Reduced mitochondrial metabolism has been associated with type 2 diabetes and exercise is linked to mitochondrial metabolism.  However, exercise also increases the formation of presumably harmful reactive oxygen species (ROS), which are mainly produced in the mitochondria.

Mitochondria are organelles in a cell where oxygen and glucose are converted into energy and free radicals, causing oxidative stress, are an inevitable by-product of mitochondrial metabolism. ROS have been reported to exert repetitive damage to individual cells of the body, promoting an increase in the prevalence of disease and aging. However, repeated exposure to mild stress such as through exercise is thought to enhance stress resistance and ultimately increased survival rates.

Researchers from Germany wanted to know if ROS is needed for the insulin sensitising effect of physical exercise in healthy humans and whether commonly used antioxidants such as Vitamins C and E may put an end to the health promoting effects of both physical exercise and oxidative stress.

The research published recently in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), evaluated the effects of a combination of Vitamin C (1000mg/day) and Vitamin E (400IU/day). The study involved 20 trained and 20 untrained subjects, with half in each group assigned antioxidant supplements. All subjects underwent a 4 week exercise training program, comprising of 85 min training sessions, 5 times a week. The study found:

• After 3 days of exercise without antioxidants, there was a 2 fold increase in the concentration of an oxidative stress marker. Taking supplements showed no significant increase in the oxidative stress marker. 
•  After 4 weeks exercise, subjects who did not use the supplements increased insulin sensitivity.  There were no changes in the subjects taking antioxidants.  
• Molecular mediators, produced by the body to defend against ROS, were also induced by exercise. This effect was blocked by antioxidant supplementation.

Dr Michael Ristow, the paper’s author proposes there is an essential role for exercise-induced ROS formation in preventing insulin resistance and type 2 diabetes, with exercise induced ROS formation appearing to result in changes in gene expression. The increase in insulin sensitivity following physical exercise is almost completely removed by daily ingestion of Vitamins C and E. Therefore, taking antioxidant supplements blocks many of the beneficial effects of exercise on metabolism.

It is possible that preventing the formation of ROS by antioxidants might actually increase, rather than decrease, the risk of type 2 diabetes.  Although there is no need to give up eating fruits and vegetables, as they may still exert health-promoting effects despite their antioxidant content due to other bio-active compounds.

Vitamin C is naturally found in many fruits and vegetables and is also found in cereals, beef, poultry and fish. Vitamin E is found in almonds, in many oils including wheat germ, corn and soybean oils and is found in mangos nuts and broccoli. With so many sources to naturally obtain nutrients it’s easy to follow the recommendation to avoid getting your antioxidants from supplements and retain the benefits from your exercise.