The effects of sleep deprivation

12 July 2023

Regular physical activity may help protect against cognitive decline in older age, but a new study from UCL suggests that this protective effect may be compromised if individuals do not get enough sleep. The research, published in The Lancet Healthy Longevity, followed 8,958 people aged 50 and over in England over a 10-year period to investigate the combined impact of sleep and physical activity on cognitive function.

The study found that individuals who were physically active but had less than 6 hours of sleep on average experienced faster cognitive decline. After 10 years, their cognitive function was comparable to those who engaged in less physical activity. Lead author Dr. Mikaela Bloomberg emphasized the importance of adequate sleep to fully benefit from physical activity and highlighted the need to consider both factors for cognitive health.

Previous studies on the topic have been limited to snapshots in time, and the researchers were surprised to discover that regular physical activity alone may not counterbalance the long-term effects of sleep deprivation on cognitive health.

The findings confirmed that sleeping between 6 and 8 hours per night and engaging in higher levels of physical activity were associated with better cognitive function. Initially, more physically active individuals performed better regardless of sleep duration. However, over the 10-year period, those who were physically active but had short sleep durations experienced a faster decline in cognitive abilities. This pattern was evident in participants aged 50 to 60, while older participants (70 and above) seemed to maintain cognitive benefits from exercise despite insufficient sleep.

Co-author Professor Andrew Steptoe emphasized the importance of identifying factors that protect cognitive function in later life to extend cognitively healthy years and potentially delay dementia diagnoses. While physical activity is already recognized by the World Health Organization for maintaining cognitive function, interventions should also consider sleep habits to maximize long-term cognitive health benefits.

The study used data from the English Longitudinal Study of Ageing (ELSA), a nationally representative cohort study in England. Participants self-reported their sleep duration and physical activity levels and were categorized into sleep groups (short, optimal, long) and physical activity groups (more active, less active). Cognitive function was assessed using memory and verbal fluency tests. The researchers adjusted for confounding factors and excluded individuals with self-reported dementia diagnoses or cognitive impairment.

However, the study had limitations, such as reliance on self-reported data. Further research is needed in diverse populations, exploring additional cognitive domains and sleep quality indicators, and utilizing objective measures like wearable activity trackers.

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