In a recently published study, Dr JAMA Network OpenResearchers 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 associated with reduced risk of cognitive decline; However, most evidence comes from short-term studies, potentially due to reverse causality bias. Research indicates that physical activity improves cognitive outcomes and reduces dementia risk, but the evidence is inconsistent.
Recent intervention studies are cautious about linking cognition to physical activity, and most existing evidence comes from observational studies with short follow-up and no prior cognitive stratification. Modeling knowledge as a continuous variable will improve statistical power.
About the study
In the current meta-analysis, researchers explored the relationship between physical exercise and cognitive decline, assessing the influence of factors such as duration of follow-up, baseline age, amount of exercise, and study quality on the association.
The team searched the PubMed, Scopus, PsycINFO, Web of Science, CINAHL and SPORTDiscus databases up to 2 November 2022 for relevant records accessible in full text in English. The cohort included prospective observational cohort or case-control studies, including persons ≥20 years of age, a follow-up period of one year or longer, and estimates of associations between physical exercise and cognition for meta-analysis. The study included validated cognitive outcome measures later in life (mean and peak age of 55 and 65 years, respectively).
The cohort included studies that assessed physical exercise using devices, questionnaires, or interviews. The primary study outcome was the relationship 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 physical exercise levels from previous recording studies, cardiorespiratory fitness levels, physical exercise, physical exercise extended beyond follow-up, and statistical redistributions for physical exercise. They excluded studies with subjective measures of cognition and assessments of cognition using disability level registers. They excluded cohorts with dementia, specific diseases or cognitive impairment at baseline.
Two reviewers independently screened titles, abstracts, and full texts of identified records, assessed quality of evidence, and retrieved data, and a third reviewer resolved disagreements if there was no consensus. The team performed random-effects modeling and used logistic regression to determine risk ratios (RRs) and regression coefficients using moderators, scatter plots, and funnel plots for physical activity. They tested conjoint hypotheses of the relationship of physical exercise with global and specific cognitive domains. They analyzed the data between January and August 2023, with a final analysis 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.. Consequently, 104 records with 341,471 individuals were analyzed. Binary outcome analysis included 45 records and 102,452 individuals; The follow-up knowledge analysis included 14 records and 41,045 individuals; And the global cognition change analysis included 25 records and 67,463 individuals.
Of the 45 studies with binary outcomes, one study, 13 studies, and 31 studies were of high, moderate, and low quality, respectively. Of the 14 studies that assessed follow-up global cognition, no studies, four studies and ten were of respective quality. Of the 25 studies evaluating changes in global cognition, there were no studies, five studies, and 20 studies of high, moderate, and low quality, respectively. Included studies were highly heterogeneous for all outcome measures, with I2 values of 70% for binary outcomes, 76% for follow-up cognition, and 67% for change in global cognition.
Physical exercise was associated with cognitive decline or impairment after funnel plot correction (pooled RR, 0.97); However, there was no statistically significant association in the follow-up analysis for more than ten years. Physical exercise was associated with follow-up domains of global cognition and their change with standardized regression coefficients of 0.030 and 0.010, respectively, obtained by trim-and-fill assessment, without moderation by participant age, follow-up duration, or dose-response association. , baseline cognition consistency, or study quality.
Specifically, verbal fluency and episodic memory were related to physical exercise with standardized regression coefficients of 0.05 and 0.03, respectively. Physical exercise amounts up to metabolic equivalents of 5,000 task minutes per week (ie, moderate to vigorous physical activity for 16 hours per week) had a higher inverse association with cognitive decline or impairment.
Overall, the study results showed a weak but positive association between physical exercise and cognitive decline that persists regardless of cognitive level or cohort age, and is crucial for population health to delay the multifactorial disease that causes dementia.
The duration, rate, type and quality of physical exercise measures of follow-up influenced the associations reported in studies with binary cognition outcomes; However, the funnel plot identified potential bias. Studies have also revealed weak associations between verbal fluency and episodic memory, with mixed results for executive function between follow-up and change analyses.