Effect of Repeated Exercise on Urinary 8-Hydroxy-deoxyguanosine Excretion in Humans

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Abstract
The purpose of this study was to investigate the effect of repeated exercise on oxidative damage to DNA in 10 well trained long distance runners who participated in an 8-day training camp. The average running distance during the camp was 30 ± 3 km/day. The amount of urinary 8-hydroxy-deoxyguanosine (8-OHdG) excretion was used to estimate the oxidative DNA damage. Urine samples were collected for both a 3-day control peRíod as well as throughout the camp. Blood samples were drawn after overnight fasting both before and after the camp. Urinary 8-OHdG excretion was significantly increased during the camp compared to the control peRíod (265.7 ± 75.5 vs. 335.6 ± 107.4 pmol/kg/day, P < 0.05). The content of 8-OHdG in the lymphocyte DNA on the day after finishing the camp did not differ from that before the camp. Plasma TBARS, LDH, CK, CK-MB, and myoglobin significantly rose after the camp (P < 0.05). The plasma β-carotene levels tended to rise after the camp, while the plasma α-tocopherol levels increased significantly after the camp (P < 0.05). These results indicate that repeated exercise augments oxidative stress and that DNA is also injured by exercise-induced reactive oxygen species. However, the oxidative damage to DNA is not accumulated by consecutive exercise, although it is sustained as long as the exercise is repeated.