Middle-aged people not getting enough sleep have less chance of seeing see the benefits of exercise when it comes to protection against a decline in skills like memory and thinking, say scientists.
They found that people in their 50s and 60s doing regular exercise but sleeping less than six hours a night had a faster decline in these skills overall.
The team, from University College London (UCL), found that after a decade, their cognitive functions – such as attention, memory and learning – were the same as those doing less physical activity, reports The Guardian.
They said their study, published in The Lancet Healthy Longevity journal, highlights the need for sleep to protect against cognitive decline as people get older.
Lead author Dr Mikaela Bloomberg, of UCL Institute of Epidemiology & Health Care, said: “Our findings suggest 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.”
For the study, the team looked at data from the English Longitudinal Study of Ageing (Elsa) from nearly 9 000 people aged 50 and over.
Their cognitive function was assessed over 10 years, with various memory and verbal fluency tests.
Questionnaires were also used to assess how long they slept and whether this was less or more than six hours. People were also asked about their levels of physical activity.
At the start of the study, those who were more physically active also had better cognitive function, regardless of how long they slept.
However, this changed over the 10-year period, with more physically active short sleepers in their 50s and 60s experiencing more rapid cognitive decline, the researchers said.
But for people aged 70 and over, the benefits of exercise on cognitive function were maintained, despite short sleep, the team added.
Co-author Professor Andrew Steptoe, of 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 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.”
Study details
Joint associations of physical activity and sleep duration with cognitive ageing: longitudinal analysis of an English cohort study
Mikaela Bloomberg, Laura Brocklebank, Mark Hamer, Andrew Steptoe.
Published in The Lancet in July 2023
Summary
Background
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.
Methods
In this longitudinal study, we analysed data from the English Longitudinal Study of Ageing collected between 1 January 2008, and 31 July 2019, with follow-up interviews every two 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.
Findings
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]).
Interpretation
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 benefits of physical activity for long-term cognitive health.
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