An analysis of the UK Biobank data revealed that “short sleepers,” those who sleep less than 6 hours daily and don’t experience daytime sleepiness, often have larger brain volumes compared to “short sleepers” with daytime sleepiness and individuals sleeping longer durations. Short sleepers tended to have slightly lower cognitive functioning than participants with longer durations of sleep as well. The study was published in the Journal of Neuroscience.
Sleep is a crucial physiological process characterized by a cycle of restorative rest for both the body and brain. It not only aids in tissue repair, hormone regulation, and immune system enhancement but also fosters memory consolidation, problem-solving, and overall mental clarity. Furthermore, sleep is indispensable for emotional stability, playing a significant role in mood and emotional resilience. Insufficient or subpar sleep can elevate the risk of chronic ailments, including heart diseases, diabetes, and obesity.
Although health professionals advocate for 7 to 9 hours of sleep nightly, approximately half of the population sleeps less. A notable 6.5% even sleeps less than 6 hours. Despite this, many don’t report excessive daytime drowsiness.
Study author Anders M. Fjell and his colleagues wanted to compare cognitive function and brain volumes of short sleepers (individuals typically sleeping less than 6 hours a night) with or without sleep problems and daytime sleepiness and individuals who sleep the recommended 7-8 hours. They note that magnetic resonance imaging data might be able to reveal many important pieces of information as studies consistently associate higher brain volume with better cognitive functioning. Atrophy in certain areas of the brain has been, on the other hand, associated with reduced cognitive functioning.
These researchers analyzed data from the UK Biobank, Lifebrain, and the Human Connectome Project (HCP). The UK Biobank offers a vast array of biometric, behavioral, and genetic data, including some participants’ magnetic resonance images. Lifebrain aggregates data from primary European brain studies, while HCP presents a freely accessible dataset of 1,143 young adults, including twins and non-twin siblings.
The data utilized spanned sleep quality indicators (from sources such as the Pittsburgh Sleep Quality Index, the Karolinska Sleep Questionnaire, or tailor-made inquiries) and cognitive ability data, with the measurement methods varying based on the data’s origin.
Participants were categorized as short sleepers (6 hours or fewer) or recommended duration sleepers. These groups were further segmented based on reported sleep issues and daytime sleepiness.
The results revealed that those with shorter sleep durations generally reported more daytime sleepiness and sleep disturbances. Imaging data indicated that brain volumes were significantly smaller in short sleepers with these problems, particularly in the brain stem and pallidum regions.
Interestingly, short sleepers without sleep disturbances had larger brain volumes compared to their longer-sleeping counterparts. However, the brain volumes of short sleepers with sleep issues and daytime drowsiness did not differ significantly from longer sleepers without these problems. In contrast, longer sleepers with sleep disturbances exhibited reduced volumes in the cerebellum, corpus callosum, and pallidum regions.
Comparisons of cognitive functioning data indicated that both groups of short sleepers tended to have somewhat lower average scores compared to longer sleepers without sleep problems.
“Some people sleep for up to 6 hours without showing lower regional brain volumes, despite sleeping within a range where smaller regional brain volumes are expected. Hence, sleep is not necessarily associated with negative structural brain outcomes. In contrast, short sleepers showed slightly lower general cognitive abilities, although the causality is unclear. The present study results suggest that there are large differences in sleep need due to genetic and environmental factors, making general recommendations about sleep duration problematic,” the study authors concluded.
The study sheds light on the link between sleep quality and cognitive functioning. However, it also has limitations that need to be considered. Notably, brain volume and cognitive ability measures used in the study are not the only possible measures of brain health and cognitive functioning. If different assessments were used, results might have not been the same. Additionally, participants were not screened for sleep disorders. This could have affected the observed relationships between sleep quality and brain properties.
The paper “Is short sleep bad for the brain? Brain structure and cognitive function in short sleepers” was authored by Anders M. Fjell, Øystein Sørensen, Yunpeng Wang, Inge K. Amlien, William F. C. Baaré, David Bartrés-Faz, Carl-Johan Boraxbekk, Andreas M. Brandmaier, Ilja Demuth, Christian A. Drevon, Klaus P. Ebmeier, Paolo Ghisletta, Rogier Kievit, Simone Kühn, Kathrine Skak Madsen, Lars Nyberg, Cristina Solé-Padullés, Didac Vidal-Piñeiro, Gerd Wagner, Leiv Otto Watne, and Kristine B. Walhovd.