Time of Day Effects in the Relationships Between Daytime Sleepiness, Current Arousal, and Cognitive Performance

Daytime sleepiness is commonly reported among older adults. Additionally, aging is associated with a shift toward greater alertness in the morning that wanes throughout the day. The impact of time of day of testing on the relationships between daytime sleepiness and cognition is unknown.

We explored the effects of time of testing in relation to self-reported daytime sleepiness/current arousal and cognition among 133 older adults.

Time of testing moderated the relationship between daytime sleepiness and immediate learning/memory, with greater sleepiness being associated with poorer performance in the afternoon, but not morning. Time of testing also moderated the relationship between current arousal and processing speed, with lower arousal being associated with worse performance in the afternoon.

These findings suggest that time of testing is important to account for when assessing sleepiness and cognition in older adults and that consideration should be given to how sleepiness is measured.