Sleep, Exercise & Cognitive Function

The results of a 10-year longitudinal study were recently published in The Lancet Healthy Longevity, detailing the associations between the cognitive trajectories of healthy adults and both sleep and physical activity. Nearly 9,000 participants between the ages of 50-95, part of the English Longitudinal Study of Ageing (ELSA), were followed every 2 years and self-reported their physical activity and sleep duration. They were given regular assessments of episodic memory and verbal fluency to observe the rate of cognitive decline (participants subsequently diagnosed with dementia were excluded from the analysis).

As might be expected, higher physical activity was associated with a higher baseline cognitive benefit, as was optimal sleep (defined as between 6-8 hours per night). Although the rate of cognitive decline (after adjustment) was not significantly different between the categories of physical activity, those reporting low sleep duration had a faster rate of decline over subsequent years.

However, a joint interaction was observed; for example, those with high physical activity and optimal sleep had a better cognitive trajectory than those with lower physical activity and short sleep, lower physical activity and optimal sleep, and those with lower physical activity and long sleep, a finding consistent among all age groups. Additionally, participants with higher physical activity and long sleep declined less rapidly than those with higher physical activity and optimal sleep.

Particularly notable was the detrimental effect of short sleep. Even among those with high physical activity, short sleep negated the benefit, with similar rates to those with low activity. While there were limitations to this study, they strongly suggest that while exercise has cognitive benefits, good sleep should be emphasized to fully realize them.