Is Physical Activity Linked to Cognitive Decline?

Is Physical Activity Linked to Cognitive Decline?

Background:

Physical exercise has been linked to a reduced risk of cognitive decline, but most evidence comes from short-term studies, which may be affected by reverse causation bias. While some research suggests that physical activity improves cognitive outcomes and reduces dementia risk, the evidence is inconsistent.

Recent interventional studies have raised concerns about correlating cognition with physical activity. Moreover, much of the existing evidence is from observational studies with brief follow-ups and lacks prior cognitive levels. Modeling cognition as a continuous variable could enhance statistical power.

About the study: In this meta-analysis, researchers examined the association between physical exercise and cognitive decline. They evaluated factors such as follow-up duration, baseline age, exercise amount, and study quality's impact on the association.

The team searched various databases for relevant records until November 2, 2022, focusing on observational prospective cohort or case-control studies involving individuals aged ≥20 years, with follow-up durations of at least one year. They included studies reporting the associations between physical exercise and cognition, with validated cognitive outcome measures in later life (mean and maximum ages of 55 and 65 years, respectively).

Studies assessing physical exercise through devices, questionnaires, or interviews were included. The primary outcome was the association between baseline physical exercise and global cognition or specific cognitive domains at follow-up.

Excluded were studies recording retrospective physical exercise levels, cardiorespiratory fitness levels, prolonged physical exercise, and those reallocating for physical exercise. Also excluded were studies using subjective cognition measures or assessing cognition via disability level registers, as well as cohorts with baseline dementia, specific diseases, or cognitive impairments.

Two reviewers independently screened records, assessed evidence quality, and retrieved data. Disagreements were resolved by a third reviewer. The team employed random-effects modeling, logistic regressions, scatter plots, and funnel plots for analysis between January and August 2023, with final analyses in December of the same year.

Results: Initially, 18,669 records were identified, with 104 records (involving 341,471 individuals) included for analysis. Physical exercise was associated with reduced cognitive decline or impairment, particularly in verbal fluency and episodic memory. However, no significant associations were found in follow-up analyses over ten years.

Physical exercise was related to follow-up global cognition and its alterations, but no moderation or dose-response associations were observed. The amount of exercise showed an inverse association with cognitive decline until 5,000 metabolic equivalents of task minutes each week.

Conclusion: The study suggests a weak but positive association between physical exercise and cognitive decline, regardless of cognition level or cohort age. This finding is essential for public health efforts to delay dementia-related diseases.

Factors such as follow-up duration, rate, exercise measurement type, and study quality influenced reported associations, with possible bias detected through funnel plots. Weak associations were observed between physical exercise and verbal fluency and episodic memory, with mixed results for executive function between follow-up and change analyses.

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