Association of long-term physical activity levels with dementia risk and cognitive function in US adults: a...

Previous cohort studies of physical activity and cognitive health have often been limited by small sample sizes, short follow-up durations, absence of long-term assessments of physical activity, and potential reverse causation. We aimed to prospectively examine the associations between long-term physical activity and multiple cognitive outcomes.

In this study, we used data from two ongoing US prospective cohorts: the Nurses' Health Study (established in 1976, comprising 121 700 female registered nurses aged 30-55 years at enrolment) and the Health Professionals Follow-Up Study (HPFS; established in 1986, comprising 51 492 male health professionals aged 40-75 years at enrolment). Discretionary physical activity was assessed approximately every 2-4 years using self-report questionnaires, beginning in 1986 for both cohorts. Total physical activity, walking, and vigorous aerobic exercise were each expressed as the summed metabolic equivalent of task hours per week. We ascertained incident dementia cases (a composite endpoint of self-reported physician-diagnosed dementia and deaths due to dementia) in eligible Nurses' Health Study participants (1990-2023) and HPFS participants (1990-2023); deaths due to dementia were confirmed using medical records, death certificates, and autopsy reports. Objective cognitive function was assessed in Nurses' Health Study participants only (1995-2008) using the Telephone Interview for Cognitive Status (TICS). Subjective cognitive decline was self-reported by Nurses' Health Study participants (followed up in 2012 and 2014) and HPFS participants (followed up in 2008, 2012, 2016, 2018, and 2020) via questionnaires with binary questions that assessed subjective cognitive concerns across multiple domains. Participants were excluded from the analysis if they had dementia, stroke, cancer, were missing total physical activity or walking data, or reported difficulties with walking at baseline. Outcomes were analysed using multivariable-adjusted regression models. We used a 4-year lag approach in our main analyses to minimise the potential for reverse causation.

Our final samples comprised 63 596 Nurses' Health Study participants and 43 440 HPFS participants for the dementia endpoints, 13 647 Nurses' Health Study participants for assessing objective cognitive function, and 29 801 Nurses' Health Study participants and 17 162 HPFS participants for assessing subjective cognitive decline. Compared with participants in the lowest quartile for total physical activity, those in the highest quartile had a lower risk of dementia (hazard ratio [HR] 0·72, 95% CI 0·68-0·76; p<0·0001 for trend) and subjective cognitive decline (relative risk [RR] 0·77, 95% CI 0·73-0·80; p<0·0001 for trend). Being in the highest versus the lowest tertile for walking or vigorous aerobic exercise was also associated with lower risk for dementia (HR 0·76, 95% CI 0·72-0·80 for walking and 0·89, 0·85-0·93 for vigorous aerobic exercise; p<0·0001 for trend for both activities) and subjective cognitive decline (RR 0·82, 95% CI 0·79-0·86 for walking and 0·89, 0·86-0·93 for vigorous aerobic exercise; p<0·0001 for trend for both activities). Additionally, being in the highest quartile of total physical activity versus the lowest quartile was associated with fewer years of age-related cognitive differences in global cognition (mean difference -1·15, 95% CI -1·69 to -0·60; p<0·0001 for trend), verbal memory (-1·27, -1·86 to -0·68; p<0·0001 for trend), and TICS score (-0·79, -1·36 to -0·23; p=0·016 for trend). Similar decreases were observed for vigorous aerobic exercise but not for walking.

Higher levels of physical activity were associated with a lower risk of dementia and better cognitive performance. These findings support physical activity as a potential strategy to promote long-term cognitive health.

US National Institutes of Health.