Physical activity's 'modest' effects on cognitive vitality

Prakash et al., in the Annual Review of Psychology, have reviewed the epidemiological literature on physical activity and exercise and their relationship to cognition and age-associated neurodegenerative diseases such as Alzheimer's disease. While the abstract uses the word "modest" to describe the effect of physical activity on preserving or enhancing cognitive vitality, the numerous studies and meta-analyses they cite demonstrate a reduction in all-cause mortality of 20-30% associated with physical activity, and a 38% reduction in risk of cognitive decline in nondemented participants with high physical activity levels, and a 35% reduction in participants with low to moderate levels. Thus there is no evidence for an increase in relative risk reduction in cognitive decline as a function of increasing levels of physical activity. Here is their abstract:

We examine evidence supporting the associations among physical activity (PA), cognitive vitality, neural functioning, and the moderation of these associations by genetic factors. Prospective epidemiological studies provide evidence for PA to be associated with a modest reduction in relative risk of cognitive decline. An evaluation of the PA-cognition link across the life span provides modest support for the effect of PA on preserving and even enhancing cognitive vitality and the associated neural circuitry in older adults, with the majority of benefits seen for tasks that are supported by the prefrontal cortex and the hippocampus. The literature on children and young adults, however, is in need of well-powered randomized controlled trials. Future directions include a more sophisticated understanding of the dose-response relationship, the integration of genetic and epigenetic approaches, inclusion of multimodal imaging of brain-behavior changes, and finally the design of multimodal interventions that may yield broader improvements in cognitive function.