The Antioxidant Effect of Exercise: A Systematic Review and Meta-Analysis

Background Physical activity has been associated with reduced oxidative stress (OS) in observational studies and clinical trials. Objective The purpose of this systematic review and metaanalysis of controlled trials was to determine the effect of physical exercise on OS parameters. Methods We conducted a systematic review of the literature up to March 2016 that included the following databases: PubMed, SCOPUS, and Web of Science. A keyword combination referring to exercise training and OS was included as part of a more thorough search process. We also manually searched the reference lists of the articles. From an initial 1573 references, we included 30 controlled trials (1346 participants) in the qualitative analysis, 19 of which were included in the meta-analysis. All trials were conducted in humans and had at least one exercise intervention and a paired control group. Using a standardized protocol, two investigators independently abstracted data on study design, sample size, participant characteristics, intervention, follow-up duration, outcomes, and quantitative data for the meta-analysis. Thus, the investigators independently assigned quality scores with a methodological quality assessment (MQA). Results The agreement level between the reviewers was 85.3 %. Discrepancies were solved in a consensus meeting. The MQA showed a total score in the quality index between 40 and 90 % and a mean quality of 55 %. Further, in a random-effects model, data from each trial were pooled and weighted by the inverse of the total variance. Physical training was associated with a significant reduction in pro-oxidant parameters (standard mean difference [SMD] -1.08; 95 % confidence interval [CI] - 1.57 to - 0.58; p < 0.001) and an increase in antioxidant capacity (SMD 1.45; 95 % CI 0.83-2.06; p < 0.001). Conclusion The pooled analysis revealed that regardless of intensity, volume, type of exercise, and studied population, the antioxidant indicators tended to increase and pro-oxidant indicators tended to decrease after training. Therefore, we conclude that exercise training seems to induce an antioxidant effect. Thus, it is suggested that people practice some kind of exercise to balance the redox state, regardless of their health status, to improve health-related outcomes.