Newly published: Sleeping worse than usual slows the brain down – regardless of age
We know that sleep is important for the brain, but how much do night-to-night variations matter in everyday life? A new study followed young and older adults to investigate how sleep duration and sleep quality affect how quickly we think the next day. The findings show that what matters most is how well you slept last night.
Researchers Johanna Schwarz, Malin Freidle, Wessel van Leeuwen, Jade Silfverling, Torbjörn Åkerstedt, and Göran Kecklund from the Department of Psychology at Stockholm University, in collaboration with Karolinska Institutet, examined how daily variations in sleep influence cognitive performance in everyday life. The study is based on data from more than 300 participants in two age groups – young adults and older adults – who were followed for three weeks.
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Participants wore an actigraphy device that measured how long they slept and also reported how they experienced their sleep each night. During the day, they completed brief smartphone-based tests that measured their processing speed – that is, how quickly and accurately they could process information.
One clear finding was that nights with shorter sleep than a participant’s own average were followed by poorer performance the next day. The same pattern was observed after nights when participants felt they had slept worse than usual. The effect was small but consistent: even relatively minor deviations from an individual’s normal sleep pattern affected the brain’s processing speed.
In contrast, it mattered less how much or how well participants slept on average compared with other people. Individuals who generally slept less than others did not perform worse. Instead, it was deviations from their own usual sleep that made the difference.
THE STUDY IN SHORT
What was studied? The relationship between day-to-day variations in sleep and cognitive processing speed in everyday life.
How was the study conducted? A 21-day intensive longitudinal study using sleep diaries, actigraphy-based sleep measurements, and smartphone-based cognitive tests to examine how sleep affects processing speed. The study included 158 young adults (18–30 years) and 168 older adults (55–75 years) without sleep disorders or diagnosed sleep-related conditions.
Key findings: Day-to-day variations in sleep within the same individual appear to matter more than differences between individuals. The findings suggest that it is not enough to “sleep well on average.” For optimal cognitive functioning in daily life, it may be important to obtain sufficient, good-quality sleep every night. Even temporary declines in sleep duration or sleep quality may be noticeable in the form of slower thinking the following day. Maintaining an adequate sleep duration each day may help prevent cognitive impairments in everyday functioning across age groups.
The older participants performed more slowly than the younger participants on the cognitive tests. However, the researchers found no clear differences between the age groups in how sensitive they were to daily changes in sleep. In other words, both younger and older adults were similarly affected by sleeping less or worse than usual.
Johanna Schwarz and Malin Freidle
Malin Freidle and Johanna Schwarz, researchers at the Department of Psychology, commented on the findings:
– Based on previous experimental research on sleep deprivation, we expected older adults to be less affected than younger adults by daily variations in sleep duration and sleep quality with regard to performance on the cognitive test. However, despite the study’s strong statistical power, we found no support for this hypothesis. Changes in sleep duration and sleep quality were associated with performance on the cognitive test, but these associations did not differ significantly between older and younger adults. The finding that older adults generally performed worse than younger adults is consistent with previous research on age-related differences in this type of task.
What’s next?
– The next step is to investigate the relationship between sleep and perceived stress in everyday life, and whether this relationship differs between younger and older adults.
Last updated: 2026-06-12
Source: Department of Psychology