Poor sleep efficiency is associated with improvements in episodic memory in older adults following a moderate-intensity exercise intervention

1. In this randomized controlled trial, improvements in episodic memory in older adults who underwent a moderate-intensity exercise program were mediated by baseline sleep efficiency—those with lower sleep efficiency demonstrated greater improvements in episodic memory following the treatment.

2. However, there were no differences in sleep parameters, including duration, sleep efficiency, and sleep onset latency, in participants who completed a medium- or high-intensity exercise program from baseline to post-intervention.

Evidence Rating Level: 1 (Excellent)

Exercise is known to provide several benefits on cognition. However, there is significant variation in these results. There are likely many moderating factors that influence the role of exercise in improving cognitive function. Sleep is associated with cognition, and exercise interventions are often associated with improved sleep quality. Thus, sleep may be an important mediating factor in this relationship between exercise and cognition. Although observational research has pointed to this link, no clinical trials have investigated sleep’s mediating role on cognition. This study aimed to assess the role of baseline sleep on the relationship between exercise and cognition in older adults.

This randomized controlled trial included 99 cognitively unimpaired participants aged 60-80. Participants were excluded if they were unable to engage in cycling-based exercise due to physical limitations, had a history of schizophrenia, schizoaffective disorder, or bipolar disorder, had untreated obstructive sleep apnea, a recent history of alcohol abuse, a history of cancer, significant medical conditions, uncontrolled diabetes, or hypertension, or had contraindications to magnetic resonance imaging. Participants were randomized to 6 months of either high-intensity exercise, moderate-intensity exercise, or an inactive control group. Participants exercised on a cycle ergometer twice a week for six months. The Pittsburgh Sleep Quality Index (PSQI) and a number of cognitive tests were administered at baseline and at the end of the intervention to investigate sleep quality and cognition, respectively. The primary outcomes were the PSQI and cognitive test scores.

The results demonstrated an improvement in episodic memory and global cognition in the moderate-intensity exercise group following the intervention. However, those in the moderate-intensity group with a lower sleep efficiency of <75% at baseline demonstrated improvements in episodic memory, while those with a higher sleep efficiency did not. Similarly, everyone in the moderate-intensity group showed improvements in cognition, except for those with a sleep efficiency in the 75-84% range. There were no differences in sleep variables in any of the groups following the exercise intervention. However, the study was limited by the self-reported nature of sleep variables, which may have introduced bias. Nonetheless, the present study demonstrated that those with poor sleep efficiency may have the greatest cognitive benefit from exercise interventions.

Click to read the study in International Journal of Geriatric Psychiatry

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