Urinary levels of 8-hydroxydeoxyguanosine as a marker of oxidative damage in road cycling

We have determined the urinary 8-hydroxydeoxyguanosine (8-OHdG) levels of eight professional cyclists during a 4-day and a 3-week stage races. Monitoring of heart rates was used to establish zones corresponding to different intensities of exercise. The urinary 8-OHdG excretion, expressed by body weight, increased significantly in the first day or the first week of each race, respectively, and did not show further increases thereafter. Maximum 8-OHdG levels were reached in parallel to longer times spent at high intensities of exercise. Urinary excretion of creatinine increased with exercise, and changes in 8-OHdG levels were not detected when corrected by creatinine excretion. Serum glutathione concentrations did not change significantly at any point during exercise. We conclude that road cycling courses with an oxidative damage to DNA, which is sustained as long as the exercise is repeated. Both adaptation of antioxidant defenses and a decreased capacity to maintain a high intensity of effort may contribute to explain the absence of progressive increases in 8-OHdG excretion. The results of this study also confirm that the correction procedure using the amount of creatinine excreted should not be used when studying effects of exercise on urinary 8-OHdG.