A recent study published in the April 2025 issue of Alzheimer's & Dementia reveals that sleeping nine or more hours per night is associated with poorer cognitive performance. The effect is particularly pronounced among individuals with depressive symptoms.
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The research involved 1,853 adults aged 27 to 85, with an average age of 50, of whom 57% were women. All participants were free from dementia and had not experienced a stroke. They were divided into four groups based on their mental health and antidepressant use: those without depression symptoms and not on medication, those with depression symptoms but not on medication, those on antidepressants without depression symptoms, and those both with depression symptoms and on antidepressants.
Participants who reported sleeping nine or more hours per night generally performed worse on cognitive tests measuring memory, visual-spatial skills, and executive function compared to those who slept between six and nine hours. This relationship was notably stronger in participants exhibiting symptoms of depression, regardless of their use of antidepressants. Additionally, long sleepers tended to report more depressive symptoms.
Experts typically recommend that healthy adults aim for seven to eight hours of sleep each night. While this study does not establish a causal link between reduced sleep and the prevention or treatment of depression and mental health disorders, it may provide insights into the interplay between sleep duration and mental health.