This study examined the cognitive function of 8,958 people who were enrolled in the English Longitudinal Study of Ageing aged 50+ over ten years, investigating how different combinations of sleep and physical activity habits might affect cognitive function over time. Their findings reveal that those who were more physically active but had less sleep (under 6 hours on average) experienced overall quicker cognitive decline, having the equivalent cognitive function as their peers who did less physical activity after 10 years.
Participants provided information on how long they slept on an average weeknight and were divided into 3 sleep groups: short sleepers who slept less than 6 hours, optimal sleepers who slept 6-8 hours, and long sleepers who slept more than 8 hours a night. Participants were also given a score based on the frequency and intensity of reported physical activity and were divided into 2 groups: more physically active and less physically active. Episodic memory testing and verbal fluency testing were used to assess participants’ cognitive function.
“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,” said Lead author Dr. Mikaela Bloomberg (UCL Institute of Epidemiology & Health Care). “Previous studies examining how sleep and physical activity might combine to affect cognitive function have primarily been cross-sectional — only focusing 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.”
The research reported that sleeping between 6-8 hours per night paired with high levels of physical activity was found to be linked with better cognitive function, which is in line with previous research.
Those who were more physically active had better cognitive function regardless of how long they were sleeping at the beginning of the study, however, this changed over 10 years, with the more physically active but short sleepers experiencing quicker cognitive decline. The decline was true for those in their 50s and 60s group, but for those aged 70+ the cognitive benefits of exercise appeared to be maintained despite short sleep.
“It is important to identify the factors that can protect cognitive function in middle and later life as they can serve to prolong our cognitively healthy years and, for some people, delay a dementia diagnosis,” said Co-author Professor Andrew Steptoe (UCL Institute of Epidemiology & Health Care). “The World Health Organisation already identifies physical activity as a way to maintain cognitive function, but interventions should also consider sleep habits to maximise long-term benefits for cognitive health.”
Adjustments were made to take into account a number of confounding factors, and people with a dementia diagnosis or cognitive impairments were excluded from the study so that behavior changes linked to preclinical Alzheimer’s disease, like sleep disturbances, did not inadvertently affect the results. However, the study was not without limitations such as relying on the participants to self-report sleep duration and physical activity.
