Exercise and Oxidative Stress: Implications in Health and Disease

Abstract

This thesis presents studies investigating the effects of exercise on free radical production as measured by ex vivo Electron Spin Resonance (ESR) spectroscopy and the by-products of lipid peroxidation.

It has been proposed that exercising in hypoxia may increase free radical production. Thus study one investigated the effects of aerobic exercise performed in normobaric hypoxia (F₁O₂ = 16%) on free radical production. Results demonstrate that hypoxic exercise does not increase (time x group, P > 0.05) systemic free radical levels. However, exercise performed at 55% V̇O_2peak markedly increased (rest vs. exercise, P < 0.05) the concentration of free radical species and lipid hydroperoxides (LH) in systemic blood. This increase was related to an exercise-induced increase (rest vs. exercise, P < 0.05) in oxygen consumption, implicating the mitochondria as a potential source of free radicals.

Type 1 diabetes is a disorder characterised by compromised antioxidant defences and increased oxidative stress. Study two investigated the effects of exhaustive exercise on these parameters in type 1 diabetic patients. No selective exercise difference (time x group, P > 0.05) was observed in free radical production between groups, although, diabetic patients had a higher systemic concentration of free radicals and LH (diabetic vs. control, P < 0.05). In addition, exhaustive exercise increased overall free radical and LH concentration (rest vs. exercise, P < 0.05). These changes may be related to glucose auto-oxidation and mitochondrial electron 'leakage' as potential sources of increased free radical production.

Study three determined the effects of exercise and ascorbic acid supplementation on free radical production in these patients. Ascorbic acid supplementation did not selectively decrease free radical production in type 1 diabetic patients (group x treatment, P > 0.05), however, ascorbic acid supplementation decreased overall oxidative stress levels (ascorbic acid vs. placebo, P < 0.05) and free radicals post-exercise (time x treatment, P < 0.05). This research demonstrates that ascorbic acid is an effective antioxidant in decreasing oxidative stress in human blood.

A series of in vitro studies were performed in order to attempt to identify the origin of the free radical species. These results suggest that the free radicals are oxygen-centred and derived from the oxidation of phospholipid membranes. This work demonstrates that (1) physical exercise per se can increase oxygen-centred free radical production, (2) type 1 diabetic patients are more susceptible to oxidative stress, and (3) ascorbic acid is effective in attenuating oxidative stress levels in humans.

Date of Award	Feb 2002
Original language	English