I give up. If anything was supposed to have been proven I would have thought it would be that exercise has a beneficial effect on brain health and cognition. Now
Ciria et al. offer the following in Nature Human Biology:
Extensive research links regular physical exercise to an overall enhancement of cognitive function across the lifespan. Here we assess the causal evidence supporting this relationship in the healthy population, using an umbrella review of meta-analyses limited to randomized controlled trials (RCTs). Despite most of the 24 reviewed meta-analyses reporting a positive overall effect, our assessment reveals evidence of low statistical power in the primary RCTs, selective inclusion of studies, publication bias and large variation in combinations of pre-processing and analytic decisions. In addition, our meta-analysis of all the primary RCTs included in the revised meta-analyses shows small exercise-related benefits (d = 0.22, 95% confidence interval 0.16 to 0.28) that became substantially smaller after accounting for key moderators (that is, active control and baseline differences; d = 0.13, 95% confidence interval 0.07 to 0.20), and negligible after correcting for publication bias (d = 0.05, 95% confidence interval −0.09 to 0.14). These findings suggest caution in claims and recommendations linking regular physical exercise to cognitive benefits in the healthy human population until more reliable causal evidence accumulates.
I can not offer an informed opinion on this abstract because my usual access to journals through the University of Wisconsin library does not work with Nature Human Behavior. However, I can point you to an
excellent commentary by Claudia Lopez Lloreda that discusses the meta-analysis done by Ciria et al. and gives a summary of several recent studies on exercise and brain health.
