Researchers from the University College London (UCL) have made a significant discovery regarding the impact of physical exercise and sleep on cognitive health deterioration as we age.

According to their study, regular physical activity can protect against cognitive health decline over time. However, this protective effect may be compromised in individuals who do not get enough sleep.

The study, which was published in The Lancet Healthy Longevity, involved the analysis of cognitive function over a 10-year period in a group of 8,958 individuals aged 50 and above in England. The researchers examined how various combinations of sleep duration and physical exercise habits influenced participants' cognitive performance over time.

The findings revealed that individuals who were more physically active but slept for fewer than six hours on average experienced a faster overall cognitive decline.

Surprisingly, their cognitive abilities were found to be on par with those of those who engaged in less physical activity after a decade.

Dr Mikaela Bloomberg, the lead author from the UCL Institute of Epidemiology and Health Care, emphasised that sufficient sleep appears to be necessary to fully reap the cognitive benefits of physical activity.

It highlights the importance of considering both sleep and physical activity together when addressing cognitive health.

Previous studies on the interplay between sleep and physical activity have mainly been cross-sectional, providing only a snapshot of the situation.

The researchers were surprised to find that regular physical exercise might not always be enough to offset the long-term effects of sleep deprivation on cognitive health.

The study also confirmed previous research showing that sleeping between six and eight hours per night, along with higher levels of physical activity, was associated with better cognitive function.

Initially, individuals who were more physically active had better cognitive function regardless of their sleep duration.

However, this changed over the 10-year period, as physically active individuals with short sleep durations experienced a more rapid cognitive decline, particularly those in their 50s and 60s.

Interestingly, older participants aged 70 and above seemed to maintain cognitive benefits from exercise despite getting less sleep.

Professor Andrew Steptoe, a co-author from the UCL Institute of Epidemiology and Health Care, stressed the importance of identifying factors that can protect cognitive function as people age.

These factors could extend the period of cognitive health and potentially delay the onset of dementia. He suggested that interventions to maintain cognitive function should not only focus on physical activity but also consider individuals' sleep habits to maximise long-term benefits.

To conduct the study, the researchers utilised data from the English Longitudinal Study of Ageing (ELSA), a nationally representative cohort study of the English population.

Participants reported their average sleep duration on weeknights and were categorised into three sleep groups: short (less than six hours), optimal (six to eight hours), and long (greater than eight hours).

They also received a score based on their self-reported physical activity level and were divided into two groups: more physically active (top third of scorers) and less physically active (remaining two-thirds). Cognitive function was evaluated through an episodic memory test and a verbal fluency test while adjusting for potential confounding factors.

However, it is important to acknowledge certain limitations of the study. The researchers relied on participants' self-reported sleep duration and physical activity, which may not be entirely accurate.

Future research may need to replicate these findings in more diverse study populations, examine additional cognitive domains and sleep quality measures, and use objective measures such as wearable physical activity trackers.

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