Abstract Study Objectives Knowledge about how day-to-day variations in sleep affect cognitive performance in real-world contexts is currently limited. This study investigated how daily fluctuations in sleep duration, efficiency and quality affect next-day processing speed, and tested whether these associations differ between young and older adults. Methods 158 young (18-30 years) and 168 older adults (55-75 years) participated in a 21-day intensive longitudinal design. Sleep duration and efficiency were measured using actigraphy, while sleep quality was assessed via sleep diaries. Processing speed was measured using a 60s smartphone-based Digit Symbol Substitution Task, administered up to 8 times per day. Multilevel mixed models tested the within-and between-person effects of sleep duration, sleep efficiency and sleep quality, as well as the effect of age group on processing speed. Results Within-person, a sleep duration shorter than their own average (p.001), and a sleep quality poorer than their own average (p.05) predicted poorer next-day performance. Between-person differences in sleep duration, sleep efficiency and sleep quality were not significantly associated with processing speed. Older adults showed worse performance than young adults (p.001), but the effect of daily sleep fluctuations on performance did not significantly vary between age groups. Conclusions Daily fluctuations in sleep duration and sleep quality are linked to processing speed in young and older adults in real-world contexts. Results suggest that within-person, day-to-day variations in sleep may be more important than between-person differences. Maintaining an adequate sleep duration each day may help prevent cognitive impairments in daily functioning across age groups.
Schwarz et al. (Tue,) studied this question.