From previous studies we know that maintaining a regular physical exercise routine can provide protection against cognitive decline associated with ageing. This is what translates into the popular mens sana in corpore. However, a recent study carried out by experts from University College London, has discovered that this beneficial effect is reduced in those individuals who cannot get a sufficient and comforting night’s rest.
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 habits and physical activity might affect people’s cognitive function over time.
They found that people who were more physically active but got little sleep (less than six hours on average) had faster overall cognitive decline, meaning that after 10 years their cognitive function was equivalent to that of their peers who did less physical activity.
Lead author of this paper, Dr Mikaela Bloomberg, from the UCL Institute of Epidemiology and Health Care, said: “Our study suggests that we may need to get enough sleep to reap 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 been mostly cross-sectional, only focusing on a snapshot in time, and we were surprised that regular physical activity is not always enough to counteract the effects long-term effects of sleep deprivation on cognitive health.
How many hours of sleep to get the cognitive benefits of exercise
The study found, in line with previous research, that getting six to eight hours of sleep a 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 much sleep they got at the start of the study. This changed over the 10-year period, with more physically active people getting little sleep (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 hold, despite little sleep.
Research co-author Professor Andrew Steptoe said: “It is important to identify factors that may protect cognitive function in midlife and old age, as they may serve to prolong our cognitively healthy years and, for some people, delay a diagnosis of dementia.
“The World Health Organization already identifies physical activity as a way to maintain cognitive function, but interventions must also consider sleep habits to maximize long-term benefits for cognitive health.”
For the study, the researchers used data from the English Longitudinal Study of Aging (ELSA), a nationally representative cohort study of the English population. Participants were asked how much sleep they got on an average weeknight and were divided into three sleep groups: short (less than six hours), optimal (six to eight hours), and long (more than eight hours).
They were also given a score based on self-reported frequency and intensity of 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 list of 10 words, both immediately and after a delay) and a verbal fluency test (asking participants to name as many animals as as they could in a minute).
The researchers adjusted for a number of confounding factors, such as that the participants have taken the same cognitive test before and are therefore likely to perform better. They also excluded people with self-reported diagnoses of dementia and those whose test scores indicated some cognitive impairment, so that behavioral changes linked to preclinical Alzheimer’s disease (such as sleep disturbances) did not inadvertently affect the results.
As for the limitations of the study, the researchers relied on participants self-reporting sleep duration and physical activity. Next steps, the authors said, may be to replicate the results in more diverse study populations, examine more cognitive domains and more sleep quality domains, and use objective measures like a wearable fitness tracker.
Source: UCL
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