People who take regular physical exercise but suffer from a lack of sleep may be negating the benefits of their activity, according to a study published today.
A study by researchers at University College London, UK, looked at cognitive function over 10 years in 8,958 people aged 50 and over in England.
It found individuals who were more physically active but had less than six hours’ sleep on average had faster overall cognitive decline.
Writing in Lancet Healthy Longevity, the researchers say this meant that after 10 years their cognitive function was equivalent to peers who did less physical activity.
Lead author Dr Mikaela Bloomberg, of 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.”
They found 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. While the decline was seen in those in their 50s and 60s, but for over 70s, the cognitive benefits of exercise appeared to be maintained, despite short sleep.
For the study, the team used data from the English Longitudinal Study of Ageing (ELSA), in which participants were asked how long they slept on an average weeknight.
They 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 and a verbal fluency test.
Bloomberg M, Brocklebank L, Hamer M et al. Joint associations of physical activity and sleep duration with cognitive ageing: longitudinal analysis of an English cohort study. Lancet Healthy Longevity 5 July 2023; doi: 10.1016/S2666-7568(23)00083-1
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