Summary: Not getting sufficient sleep could offset the cognitive benefits gained from regular physical activity.
Researchers studied cognitive function over 10 years in nearly 9000 English people aged 50 and over. They discovered those who were physically active but slept less than six hours had faster cognitive decline.
Therefore, after a decade, their cognitive function resembled less physically active peers.
The study demonstrated a rapid cognitive decline in physically active individuals aged in their 50s and 60s, who slept less than six hours a night.
For older participants (70 and over), the cognitive benefits of exercise were maintained despite short sleep.
The findings highlight the importance of considering sleep and physical activity together for cognitive health.
Regular physical activity may protect against cognitive decline as we get older, but this protective effect may be diminished for people who are not getting enough sleep, according to a new study by UCL researchers.
The study, published in The Lancet Healthy Longevity, looked at cognitive function over 10 years in 8,958 people aged 50 and over in England. The research team investigated how different combinations of sleep and physical activity habits might affect people’s cognitive function over time.
They found that people who were more physically active but had short sleeps – less than six hours on average – had faster cognitive decline overall, meaning that after 10 years their cognitive function was equivalent to peers who did less physical activity.
Lead author Dr Mikaela Bloomberg (UCL Institute of Epidemiology & Health Care) said: “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.
“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 study found, in line with previous research, that sleeping between six and eight hours per night and higher levels of physical activity were linked to better cognitive function.
Those who were more physically active also had better cognitive function regardless of how long they slept at the start of the study. This changed over the 10-year period, with more physically active short sleepers (less than six hours) experiencing more rapid cognitive decline.
This rapid decline was true for those in their 50s and 60s in this group, but for older participants (aged 70 and over) the cognitive benefits of exercise appeared to be maintained, despite short sleep.
Co-author Professor Andrew Steptoe (UCL Institute of Epidemiology & Health Care) said: “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.
“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.”
For the study, the researchers used data from the English Longitudinal Study of Ageing (ELSA), a nationally representative cohort study of the English population.
Participants were asked how long they slept on an average weeknight and were split into three sleep groups: short (less than six hours), optimal (six to eight hours) and long (greater than eight hours).
They were also given a score based on the frequency and intensity of self-reported physical activity and divided into two groups: more physically active (the top third of scorers) and less physically active (the other two thirds).
Cognitive function was assessed on the basis of an episodic memory test (asking participants to recall a 10-word list, both immediately and after a delay) and a verbal fluency test (asking participants to name as many animals as they can in a minute).
The researchers adjusted for a number of confounding factors, such as participants having done the same cognitive test before and therefore being likely to perform better.
They also excluded people with self-reported dementia diagnoses and those whose test scores indicated some cognitive impairment, so that behaviour changes linked to preclinical Alzheimer’s disease (such as sleep disturbance) did not inadvertently affect the results.
In terms of study limitations, the researchers relied on participants self-reporting their sleep duration and physical activity. The next steps, the researchers said, may be to repeat the results in more diverse study populations, examine more cognitive domains and more domains of sleep quality, and use objective measures such as a wearable physical activity tracker.
Funding: The research was funded by the UK’s Economic and Social Research Council.
About this exercise, sleep, and cognition research news
Author: Mark Greaves Source: UCL Contact: Mark Greaves – UCL Image: The image is credited to Neuroscience News
Joint associations of physical activity and sleep duration with cognitive ageing: longitudinal analysis of an English cohort study
Physical activity and sleep duration are key factors associated with cognitive function and dementia risk. How physical activity and sleep interact to influence cognitive ageing is not well explored. We aimed to examine the associations of combinations of physical activity and sleep duration with 10-year cognitive trajectories.
In this longitudinal study, we analysed data from the English Longitudinal Study of Ageing collected between Jan 1, 2008, and July 31, 2019, with follow-up interviews every 2 years. Participants were cognitively healthy adults aged at least 50 years at baseline. Participants were asked about physical activity and nightly sleep duration at baseline. At each interview, episodic memory was assessed using immediate and delayed recall tasks and verbal fluency using an animal naming task; scores were standardised and averaged to produce a composite cognitive score. We used linear mixed models to examine independent and joint associations of physical activity (lower physical activity or higher physical activity, based on a score taking into account frequency and intensity of physical activity) and sleep duration (short [<6 h], optimal [6–8 h], or long [>8 h]) with cognitive performance at baseline, after 10 years of follow-up, and the rate of cognitive decline.
We included 8958 respondents aged 50–95 years at baseline (median follow-up 10 years [IQR 2–10]). Lower physical activity and suboptimal sleep were independently associated with worse cognitive performance; short sleep was also associated with faster cognitive decline. At baseline, participants with higher physical activity and optimal sleep had higher cognitive scores than all combinations of lower physical activity and sleep categories (eg, difference between those with higher physical activity and optimal sleep vs those with lower physical activity and short sleep at baseline age 50 years was 0·14 SDs [95% CI 0·05–0·24]). We found no difference in baseline cognitive performance between sleep categories within the higher physical activity category. Those with higher physical activity and short sleep had faster rates of cognitive decline than those with higher physical activity and optimal sleep, such that their scores at 10 years were commensurate with those who reported low physical activity, regardless of sleep duration (eg, 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 0·20 SDs [0·08–0·33]; difference between those with higher physical activity and optimal sleep and those with lower physical activity and short sleep was 0·22 SDs [0·11–0·34]).
The baseline cognitive benefit associated with more frequent, higher intensity physical activity was insufficient to ameliorate the more rapid cognitive decline associated with short sleep. Physical activity interventions should also consider sleep habits to maximise benefis of physical activity for long-term cognitive health.