Daily fluctuations in sleep duration and quality affect next-day processing speed performance in young and older adults: An intensive longitudinal everyday life study over 21 days

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 A total of 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 60 s smartphone-based Digit Symbol Substitution Task, administered up to eight 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