Getting either too much or too little sleep is associated with changes in the brain that have been shown to increase the risk of stroke and dementia later in life, researchers from  Yale School of Medicine say. “Conditions like stroke or dementia are the end-stage result of a long process that ends tragically,” says Santiago Clocchiatti-Tuozzo, MD, first author of the study. “We want to learn how to prevent these processes before they happen.”

In one of the largest neuroimaging studies of its kind to date, the Yale team examined brain images of close to 40,000 healthy, middle-aged participants to evaluate how sleeping habits might impact two measures of brain health: white matter hyperintensities (WMH), which are lesions on the brain indicating brain aging, and fractional anisotropy, which measures the uniformity of water diffusion along nerve axons. More WMH, larger WMH, and lower fractional anisotropy are associated with increased risk of stroke and dementia.

Researchers found that compared with optimal sleep (7-9 hours per night), participants with short sleep had a higher risk of having WMH, larger WMH volume where WMH was present, and lower fractional anisotropy. Long sleep (averaging more than 9 hours per night) was associated with lower fractional anisotropy and with larger WMH volume, but not with the risk of actually having WMH.

“These findings add to the mounting evidence that sleep is a prime pillar of brain health,” said Clocchiatti-Tuozzo. “It also provides evidence toward helping us understand how sleep and sleep duration can be modifiable risk factors for brain health later in life.”

Overall, according to the researchers, the study highlights middle age as an important time to adjust sleeping habits to support brain health.

To read the full study, published in the Journal of the American Heart Association, click here