In a recent study published in JAMA Network Open, researchers examined the link between physical exercise and cognitive decline, examining domain-specific and global cognition and examining dose-response associations and potential moderators.
Physical exercise is related to a reduced risk of cognitive decline; however, most evidence is from short-term studies, potentially due to reverse causation bias. Research indicates that physical activity improves cognitive outcomes and reduces dementia risk, but the evidence is inconsistent.
Recent interventional studies caution about linking cognition with physical activity, and most existing evidence comes from observational studies with brief follow-ups and no prior cognitive levels. Modeling cognition as a continuous variable would improve statistical power.
About the study
In the present meta-analysis, researchers explored the association between physical exercise and cognitive decline, evaluating the impact of factors like follow-up duration, baseline age, exercise amount, and the quality of the included studies on the association.
The team searched the PubMed, Scopus, PsycINFO, Web of Science, CINAHL, and SPORTDiscus databases through 2 November 2022 for relevant records with full text accessible in English. The team included observational prospective cohort or case-control studies, including individuals aged ≥20 years, follow-up durations of one year or more, and estimates of the associations between physical exercise and cognition for the meta-analysis. The included studies reported validated cognitive outcome measures in later life (mean and maximum ages of 55 and 65 years, respectively).
The team included studies evaluating physical exercise using devices, questionnaires, or interviews. The primary study outcome was the association between baseline physical exercise and global cognition or specific cognitive domains (such as episodic memory, executive function, verbal ability, verbal naming and fluency, processing speed, visuospatial ability, and working memory) at follow-up.
The team excluded studies recording retrospective physical exercise levels, cardiorespiratory fitness levels, bouts of physical exercise, physical exercise extending beyond the follow-up, and statistical reallocations for physical exercise. They also excluded studies including subjective measures of cognition and those assessing cognition using disability level registers. They also excluded cohorts with dementia, specific diseases, or cognitive impairments at baseline.
Two reviewers independently screened titles, abstracts, and full texts of the identified records, assessed evidence quality, and retrieved data, and a third reviewer solved disagreements in case of no consensus. The team performed random-effects modeling and used logistic regressions to determine the risk ratios (RRs) and regression coefficients using moderators, scatter plots, and funnel plots for physical exercise. They examined pooled estimations of the relationships of physical exercise with global and particular cognitive domains. They analyzed data between January and August 2023, with final analyses in December of the same year.
Initially, the team identified 18,669 records and excluded 17,861 during title-abstract screening and 703 during full-text screening. As a result, 104 records, including 341,471 individuals, were analyzed. The binary outcome analysis included 45 records and 102,452 individuals; the follow-up cognition analysis included 14 records and 41,045 individuals; and the global cognition alterations analysis included 25 records and 67,463 individuals.
Among 45 studies with binary outcomes, one study, 13 studies, and 31 studies were of high, medium, and low quality, respectively. Among 14 studies assessing follow-up global cognition, no study, four studies, and ten were of the corresponding quality, respectively. Among the 25 studies evaluating global cognition changes, no study, five studies, and 20 were of high, medium, and low quality, respectively. The included studies for all outcome measures were highly heterogeneous, with I2 values of 70% for binary outcomes, 76% for follow-up cognition, and 67% for changes in global cognition.
Physical exercise was related to lowered cognitive decay or impairment after funnel plot corrections (pooled RR, 0.97); however, there were no statistically significant associations in follow-up analyses over more than ten years. Physical exercise was related to follow-up domains of global cognition and their alterations with standardized regression coefficients of 0.030 and 0.010, respectively, obtained by trim-and-fill assessment, without moderation or dose-response associations by participant age, follow-up duration, baseline cognition adjustments, or study quality.
In particular, verbal fluency and episodic memory were related to physical exercise with standardized regression coefficients of 0.05 and 0.03, respectively. The amount of physical exercise had a higher inverse association with cognitive decay or impairment until 5,000 metabolic equivalents of task minutes each week (i.e., moderate to vigorous physical activity for 16 hours each week).
Overall, the study findings showed a weak but positive association between physical exercise and cognitive decline that persisted regardless of cognition level or cohort age and is crucial for population health to postpone multifactorial diseases causing dementia.
Follow-up duration, rate, physical exercise measurement type, and quality influenced the association reported in studies with binary cognition outcomes; however, funnel plots detected possible bias. The study also revealed weak associations between verbal fluency and episodic memory, with mixed results for executive function between follow-up and change analyses.