Physical inactivity is a known risk factor for dementia, and research has consistently shown that regular physical activity is associated with better cognitive function and a reduced risk of dementia. However, the relationship between structured exercise interventions and cognitive function has been less clear. A recent study published in the International Journal of Geriatric Psychiatry has shed light on this issue, suggesting that the effects of exercise on cognition may be influenced by baseline sleep quality.
Dementia is a growing concern worldwide, with an aging population, and identifying modifiable risk factors for cognitive decline is crucial. Physical inactivity has been identified as a significant risk factor for dementia, making it an important area of study. While observational research has consistently linked physical activity to better cognitive function, studies investigating the effects of structured exercise interventions on cognition have produced mixed results.
One factor that might contribute to these inconsistencies is sleep. Sleep plays a vital role in cognitive function, and poor sleep is associated with cognitive decline. Observational research has suggested that sleep may moderate the relationship between physical activity and cognitive function, but this has not been extensively explored in randomized clinical trials.
“Greater exercise has been linked to better memory and thinking skills in older adults,” explained study author Kelsey R. Sewell (@kelseysewell_), a postdoctoral research Fellow at Murdoch University. “However, we know that exercise behaviours do not exist in isolation from other lifestyle behaviours, and in particular, can influence, and be influenced by, sleep quality. Further, sleep quality is also closely linked to memory and thinking skills. We therefore were interested in investigating how sleep and exercise might interact to influence memory and thinking skills in healthy older adults.”
For their study, the researchers examined data from the Intense Physical Activity and Cognition (IPAC) study, which involved 99 cognitively unimpaired older adults aged 60 to 80. These participants were divided into three groups: one engaged in high-intensity exercise, another in moderate-intensity exercise, and a control group that did not engage in exercise.
The exercise groups participated in supervised exercise sessions twice a week for six months, using a cycle ergometer. The intensity of the exercise was carefully controlled, with the moderate-intensity group cycling at a steady pace and the high-intensity group cycling with intervals of high exertion.
Baseline sleep data was collected from all participants, and subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI), a widely-used self-report measure of sleep quality. The PSQI measures various aspects of sleep, including duration, efficiency, and onset latency.
Cognitive assessments were conducted at baseline and after the six-month intervention, covering various aspects of cognitive function, including memory, attention, and executive function. These assessments were used to create composite scores for different cognitive domains.
In the moderate-intensity exercise group, individuals with poorer baseline sleep efficiency (<75%) showed significant improvements in episodic memory and global cognition after the exercise intervention. However, those with better sleep efficiency did not experience similar cognitive improvements. This suggests that exercise may have a more substantial impact on cognition in individuals with poorer sleep efficiency.
“We found that moderate intensity exercise may have the greatest positive impact on memory in those with self-reported poorer sleep. Thus, we conclude that exercise may compensate for some of the negative effects poor sleep has on memory functioning. However, further research is required to confirm our findings.”
Surprisingly, the exercise intervention did not lead to significant changes in sleep duration, sleep efficiency, or sleep onset latency for either exercise group compared to the control group. This finding contradicts previous research that suggested exercise could improve sleep quality.
“We also found that our exercise intervention did not influence self-reported sleep quality, which was surprising given that previous research shows a link between greater exercise and better sleep. This may be because our sample were already reporting sleep metrics within the normal range at baseline, and studies in those with poor sleep may see a greater effect of exercise on sleep outcomes.”
While this study provides valuable insights into the relationship between exercise, sleep, and cognition, it has some limitations. The use of self-report measures for sleep may introduce recall bias, and the study focused on a relatively homogeneous group of older adults. Future research should explore these associations in more diverse populations and consider objective sleep measurements. Additionally, the study only examined the immediate post-intervention effects of exercise on cognition, so long-term effects remain to be studied.
“We used a measure of self-reported sleep – which could be subject to bias or fallible memory. However, these measures have proven useful for predicting important health outcomes, and may capture other information that objective sleep measures cannot. This study is one of the first of its kind, and further research needs to be conducted to confirm our conclusions.”
This study highlights the importance of considering sleep quality when investigating the effects of exercise on cognition. It suggests that individuals with poorer sleep efficiency may benefit the most from moderate-intensity exercise interventions, especially in terms of memory and overall cognitive function.
Understanding the complex interplay between exercise, sleep, and cognition is crucial in the effort to develop effective interventions for cognitive health, potentially delaying the onset of cognitive decline and dementia. Further research is needed to explore the mechanisms behind these associations and to develop comprehensive lifestyle interventions that can maximize cognitive benefits in older adults.
The study, “The influence of baseline sleep on exercise-induced cognitive change in cognitively unimpaired older adults: A randomised clinical trial“, was authored by Kelsey R. Sewell, Stephanie R. Rainey-Smith, Jeremiah Peiffer, Hamid R. Sohrabi, James Doecke, Natalie J. Frost, Shaun J. Markovic, Kirk Erickson, and Belinda M. Brown.
