Effects of aerobic exercise on cognitive function in adults with major depressive disorder: A systematic review and meta-analysis

Background: Major Depressive Disorder (MDD) is a highly prevalent psychiatric disorder that impairs the cognitive function of individuals. Aerobic exercise stands out as a promising non-pharmacological intervention for enhancing cognitive function and promoting brain health. While positive impacts of aerobic exercise on executive function in adults with depression have been documented, a comprehensive understanding of its benefits on overall cognitive function, including memory, attention, and processing speed, along with key moderating factors in adults with MDD, remains unexplored. The purpose of the systematic review and meta-analysis was to investigate the effects of aerobic exercise on overall cognitive function in adults with MDD, and to explore whether cognitive sub-domains, aerobic exercise characteristics, and study and sample variables modify the effects of aerobic exercise on cognition. Methods: Six English electronic databases (Embase, Cochrane Central, Scopus, APA PsycInfo, PubMed, Web of Science) were searched from inception to 2 April 2023. Randomized trials, including adults aged 18 years or above with a diagnosis of clinical depression, of the effects of aerobic exercise on cognitive function in adults with MDD compared to non-aerobic exercise groups were included. A three-level meta-analysis was conducted utilizing a random-effects model in R. The quality of the studies was evaluated using the Physiotherapy Evidence Database (PEDro) scale. The PROSPERO registration number is CRD42022367350. Results: Twelve randomized trials including 945 adults with MDD were included. Results indicated that aerobic exercise significantly improved overall cognitive function (g = 0.21; 95 % confidence intervals [CI] = 0.07, 0.34), and the sub-domains of memory (g = 0.25; 95 % CI = 0.06, 0.44) and executive function (g = 0.12; 95 % CI = 0.04, 0.20). Significant benefits in cognitive function were found from moderate-to-vigorous (mixed) intensity (g = 0.19; 95 % CI = 0.02, 0.37), aerobic exercise conducted 3 times per week (g = 0.23; 95 % CI = 0.10, 0.38), in sessions < 45 min (g = 0.59; 95 % CI = 0.28, 0.90), and 45-60 min (g = 0.16; 95 % CI = 0.07, 0.26), in aerobic exercise intervention <= 12 weeks (g = 0. 26; 95 % CI = 0.08, 0.44). Limitations: This review only included peer-reviewed English-language studies, which may lead to a language bias. The results of the Egger's test suggested a potential publication bias. Conclusions: Aerobic exercise is efficacious in improving overall cognitive function and the sub-domains of memory and executive function in adults with major depressive disorder.