It is actually possible to sleep too much. A study led by researchers at the University of Texas Health Science Center (UT Health San Antonio) shows that nine or more hours of sleep per night are associated with poorer cognitive performance. This is even more true for people with depression. The findings were derived from an examination of sleep duration and cognitive abilities in 1,853 participants without dementia or stroke as part of the Framingham Heart Study, an ongoing population-based cohort study led by the National Heart, Lung, and Blood Institute of the National Institutes of Health. The latest study focused on individuals aged 27 to 85, with an average age of 49.8.

How Sleep duration and Cognitive Performance are Related

“In addition, long sleepers reported symptoms of depression more often,” said Vanessa Young, MS, clinical research project manager at the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at UT Health San Antonio. Sleep may be a modifiable risk factor for cognitive decline in people with depression.” Young, who is also participating in the Translational Science PhD program at the Graduate School of Biomedical Sciences at UT Health San Antonio, is the first author of the study titled “Long sleep duration, cognitive performance, and the moderating role of depression: A cross-sectional analysis in the Framingham Heart Study” (Long sleep duration, cognitive performance, and the moderating role of depression: A cross-sectional analysis in the Framingham Heart Study), which was published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.

The authors also represent Arizona State University, the Framingham Heart Study, the Hôpital du Sacré-Coeur de Montréal, the University of Montreal, Boston University, and Monash University in Australia. “Long, but not short, sleep duration was associated with poorer overall cognitive performance and specific cognitive abilities such as memory, visuospatial abilities, and executive function,” said Sudha Seshadri, founding director of the Biggs Institute and senior author of the study. These associations were more pronounced in people with depressive symptoms, regardless of antidepressant use.

The Impact of Depression

According to the study, the importance of sleep as a vital physiological process for brain health is increasingly recognized. Sleep duration and sleep behavior disorders have been observed throughout the lifespan and occur in both normal and pathological aging. These disorders contribute to an increased risk of cognitive deficits and Alzheimer’s disease. The Global Council on Brain Health recommends that adults get 7 to 8 hours of sleep per night to maintain brain health. Several studies have shown that both excessive and insufficient sleep compared to the recommended duration is associated with impairments in cognitive domains, including memory, attention, and the ability to control other mental processes such as planning, problem solving, and impulse control.

However, the evidence is mixed, as it depends on the lifespan studied and health differences such as depression. Depression, a modifiable risk factor for cognitive decline, often occurs alongside sleep disorders. The link between sleep disorders and depression is well established: around 90% of people with depression report sleep problems, according to the study. In the new study, the researchers investigated whether depression influences the association between sleep duration and cognitive performance. The Framingham participants were divided into four groups: no depressive symptoms, no antidepressants; depressive symptoms without antidepressants; antidepressants without depressive symptoms; depressive symptoms and antidepressants.

They found that long sleep was associated with reduced overall cognitive performance, with the strongest effects occurring in individuals with depressive symptoms who were taking antidepressants or not taking them. Weaker but significant effects were observed in individuals without depressive symptoms. No significant associations were found in participants who were taking antidepressants without showing depressive symptoms. They concluded that the association between sleep duration and cognitive performance is strongest in individuals with depressive symptoms, regardless of antidepressant use. According to the researchers, future longitudinal studies with large-scale, multimodal approaches are needed to further clarify the temporal relationship between sleep disturbances and cognitive changes.