Quest Vitamins LTD,
Antioxidants and exercise
Among the many benefits of regular exercise is an improvement in insulin sensitivity and a consequent reduced risk of developing Type 2 diabetes.
Insulin is a hormone designed to lower blood sugar, stimulating the uptake of glucose by cells for energy production and storage. Type 2 diabetes develops when cells effectively fail to respond to insulin, resulting in dangerously high insulin levels. Exercise is known to stimulate the oxidation of glucose in the mitochondria of cells to meet increased energy requirements and enhance the expression of glucose transporters. The increase in the oxidation of glucose however also leads to a significant increase in free radical production as a by-product; for this reason it has been advocated that those engaged in regular exercise take anti-oxidant supplements to limit free radical damage. In a new study it has been found that, in fact, a blanket recommendation to increase antioxidant consumption when active may not be advisable.
In the study 40 individuals, half of whom trained prior to the study and half of whom did not, were randomly assigned to receive either antioxidant supplements consisting of 1g of vitamin C and 400IU of vitamin E, or a dummy pill (placebo) during four weeks of intensive exercise training. A highly significant increase in oxidative stress was observed among the non-supplemented exercisers, by contrast those receiving the antioxidants showed no significant increase in oxidative stress. Further analysis revealed that among the non-supplemented group free radical mediated changes in gene expression resulted in an increase in insulin sensitivity and an increase in the availability of superoxide dismutase and glutathione, an antioxidant produced by the body; this effect was not observed among the group receiving antioxidants.
The evidence regarding the effects of free radical exposure on insulin sensitivity is ambiguous, some research suggests that in fact free radical exposure promotes insulin resistance. One explanation for this may be that the effect of continuous free radical exposure is very different from the effect of transient increases as occurs during exercise. The study does not suggest that antioxidant supplements are not of benefit to regular exercisers, but rather that exercise levels, the timing and composition of supplements used may be of importance. It is suggested that those who are "weeken warriors" may wish to ensure a good antioxidant intake on an everyday basis to enable their bodies to better adapt to the significant increase in free radical exposure during intense bouts of exercise, meanwhile those who exercise intensely on a continuous basis may have increased antioxidant requirements.