Poor sleep reduces cognitive benefits of exercise

Key takeaways:

• Exercise may protect against cognitive decline, with lesser benefits for those who do not get enough sleep.
• Researchers said sleep habits should be considered in physical activity interventions.

Regular physical activity may protect against cognitive decline, but the benefits may be reduced for those who do not get enough sleep, according to the results of research published in The Lancet Healthy Longevity.

Mikaela Bloomberg, PhD, MS, a postdoctoral research fellow in cognitive aging epidemiology at the University College London, and colleagues wrote that both sleep duration and physical activity are key factors connected to dementia risk and overall cognitive function, but not much is yet known about how sleep and physical activity interact to influence cognitive aging.

“More physical activity has been associated with less accumulation of Alzheimer’s disease biomarkers and decreased risk of dementia, and poor sleep has been associated with greater accumulation of Alzheimer’s disease biomarkers and increased risk of dementia,” they wrote. “As such, physical activity is identified in WHO guidelines as a target to improve cognitive health.”

The researchers conducted a longitudinal analysis of an English cohort study to assess the links between combinations of sleep duration and physical activity with 10-year cognitive trajectories.

They analyzed data from 8,958 participants in the English Longitudinal Study of Aging who were cognitively healthy and aged at least 50 years at baseline. The participants were asked about nightly sleep duration and physical activity at baseline and every 2 years during follow-up interviews. Their episodic memory was evaluated at each interview, with immediate and delayed recall tasks and verbal fluency evaluated with an animal naming task.

Bloomberg and colleagues found that short sleep and lower physical activity were independently connected with worse cognitive performance, but short sleep was also associated with more rapid cognitive decline. Additionally, the link between more frequent, higher intensity physical activity and cognitive benefits was not enough to make up for the rapid cognitive decline linked to short sleep.

“Our study suggests that getting sufficient sleep may be required for us to get the full cognitive benefits of physical activity. It shows how important it is to consider sleep and physical activity together when thinking about cognitive health,” Bloomberg said in a press release.

At baseline, participants with better sleep and higher physical activity had higher cognitive scores than all combinations of lower sleep and physical activity categories. The difference between those with higher physical activity and optimal sleep vs. those with lower physical activity and short sleep at baseline was 0.14 standard deviations (SDs; 95% CI 0.05-0.24).

Those with higher physical activity and short sleep had faster rates of cognitive decline than those with higher physical activity and optimal sleep. In fact, their scores at 10 years were proportional to those who reported low physical activity, regardless of sleep duration.

The difference in cognitive performance after 10 years of follow up between those with higher physical and optimal sleep and those with lower physical activity and short sleep was 0.2 SDs (95% CI, 0.08-0.33) and the difference between those with higher physical activity and optimal sleep and those with lower physical activity and short sleep was 0.22 SDs (95% CI, 0.11-0.34).

“Previous studies examining how sleep and physical activity might combine to affect cognitive function have primarily been cross-sectional —focusing only on a snapshot in time — and we were surprised that regular physical activity may not always be sufficient to counter the long-term effects of lack of sleep on cognitive health,” Bloomberg said in the release.

In light of the findings, Bloomberg and colleagues wrote that physical activity interventions “should also consider sleep habits to maximize long-term benefits of physical activity on cognitive health, improve cognitive aging outcomes, and potentially delay onset of dementia.”

References:

• Bloomberg M, et al. Lancet Healthy Longey. 2023;doi:10.1016/S2666-7568(23)00083-1.
• Lack of sleep lessens cognitive benefits of physical activity. https://www.eurekalert.org/news-releases/994546. Published July 5, 2023. Accessed July 14, 2023.