Exercise is often cited as a major factor contributing to improved cognitive functioning. As a result, the relationship between exercise and cognition has received much attention in scholarly literature. Systematic reviews and meta-analyses present varying and sometimes conflicting results about the extent to which exercise can influence cognition. The aim of this umbrella review was to summarize the effects of physical exercise on cognitive functions (global cognition, executive function, memory, attention, or processing speed) in healthy adults ≥ 55 years of age.
This review of systematic reviews with meta-analyses invested the effect of exercise on cognition. Databases (CINAHL, Cochrane Library, MEDLINE, PsycInfo, Scopus, and Web of Science) were searched from inception until June 2023 for reviews of randomized or non-randomised controlled trials. Full-text articles meeting the inclusion criteria were reviewed and methodological quality assessed. Overlap within included reviews was assessed using the corrected covered area method (CCA). A random effects model was used to calculate overall pooled effect size with sub-analyses for specific cognitive domains, exercise type and timing of exercise.
A total of 20 met the inclusion criteria. They were based on 332 original primary studies. Overall quality of the reviews was considered moderate with most meeting 8 or more of the 16 AMSTAR 2 categories. Overall pooled effects indicated that exercise in general has a small positive effect on cognition (d = 0.22; SE = 0.04; p < 0.01). Mind–body exercise had the greatest effect with a pooled effect size of (d = 0.48; SE = 0.06; p < 0.001). Exercise had a moderate positive effect on global cognition (d = 0.43; SE = 0,11; p < 0,001) and a small positive effect on executive function, memory, attention, and processing speed. Chronic exercise was more effective than acute exercise. Variation across studies due to heterogeneity was considered very high.
The authors concluded that mind–body exercise has moderate positive effects on the cognitive function of people aged 55 or older. To promote healthy aging, mind–body exercise should be used over a prolonged period to complement other types of exercise. Results of this review should be used to inform the development of guidelines to promote healthy aging.
It seems to me that the umbrella review hides the crucial fact that many of the primary studies had major flaws, e.g. in terms of:
- lack of randomisation,
- lack of blinding.
Eleven studies investigated the effects of aerobic exercise on cognition. Only three studies investigated the effects of mind body exercise on cognition, two analysed the effects of resistance exercise, and five investigated the effects of mixed exercise interventions. I am therefore mystified how the authors managed to arrive at such a hyped conclusion in favour of the effectiveness of mind body exercises. Even an optimistic interpretation of the data would allow merely a weak indication that a positive effect might exist. To state that mind body exercises should be promoted for ‘healthy aging’ borders on the irresponsible, in my view. Surely even the most naive researcher must see that, for such a far-reaching recommendation, we would need much more solid evidence.
I strongly suspect that a proper review of the primary studies of mind body exercise with a critical evaluation of the quality of the primary studies would lead to dramatically different conclusion.