Lack of sleep dampens good effects of exercise on the brain

A new study conducted by researchers at University College London (UCL) suggests that while regular physical activity is known to protect against cognitive decline as we age, the beneficial effect may be diminished if we’re not getting enough sleep.

The study, published in The Lancet Healthy Longevity, followed 8,958 individuals aged 50 and over in England for a period of 10 years, monitoring their cognitive function. The researchers aimed to understand how different combinations of sleep and physical activity habits could impact cognitive function over time.

The findings revealed that individuals who engaged in more physical activity but had short durations of sleep, averaging less than six hours per night, experienced a faster overall cognitive decline. In fact, after 10 years, their cognitive function was comparable to that of their peers who engaged in less physical activity.

Lead author Dr. Mikaela Bloomberg from UCL Institute of Epidemiology & Health Care emphasized the importance of considering sleep and physical activity together when it comes to cognitive health. The study indicates that sufficient sleep may be necessary to reap the full cognitive benefits of physical activity. Dr. Bloomberg expressed surprise that regular physical activity alone may not always be enough to counteract the long-term effects of insufficient sleep on cognitive health.

The study also confirmed previous research by showing that sleeping between six and eight hours per night, along with higher levels of physical activity, was associated with better cognitive function. Interestingly, the cognitive benefits of exercise appeared to be maintained for older participants (aged 70 and over) who were more physically active, even if they had short sleep durations. However, for individuals in their 50s and 60s who were physically active but had less sleep, cognitive decline was more rapid.

Co-author Professor Andrew Steptoe from UCL Institute of Epidemiology & Health Care emphasized the significance of identifying factors that can protect cognitive function in middle and later life, as they can potentially prolong cognitively healthy years and delay dementia diagnosis. While the World Health Organization already recognizes physical activity as a means to maintain cognitive function, Professor Steptoe highlighted the importance of considering sleep habits as well in order to maximize long-term cognitive health benefits.

The researchers utilized data from the English Longitudinal Study of Ageing (ELSA), a comprehensive study representing the English population. Participants were divided into three sleep groups based on self-reported sleep duration: short (less than six hours), optimal (six to eight hours), and long (greater than eight hours). They were also assessed for physical activity levels and categorized as more physically active or less physically active. Cognitive function was evaluated using episodic memory and verbal fluency tests.

The study accounted for various confounding factors, such as participants having previously taken the same cognitive tests, to ensure more accurate results. Participants with self-reported dementia diagnoses or indications of cognitive impairment were excluded from the analysis to prevent the influence of preclinical Alzheimer’s disease on the findings.

It is important to note that the study has limitations, including its reliance on participants’ self-reporting of sleep duration and physical activity. Future research may involve replicating the results in more diverse study populations, exploring other cognitive domains and sleep quality measures, and utilizing objective measures like wearable physical activity trackers.

The study received funding from the UK’s Economic and Social Research Council.

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