How we sleep may have lasting impacts for our brain health as we age. A new University of Arizona study has found that several common sleep behaviors may be linked to signs of brain aging.
The study , published in the journal Alzheimer's & Dementia, used existing brain scans and questionnaire responses from more than 23,000 middle-aged and older adults from a large biomedical database. The work is part of a broader collaborative project between the U of A Department of Psychology , the Zuckerman College of Public Health and the University of Southern California.
The researchers identified three sleep behaviors distinctly associated with a marker of brain aging in healthy people: sleeping outside the recommended seven-to-nine-hour range, frequent daytime napping and sleeplessness. All three were linked to greater volume of white matter lesions, areas of damage in the brain that can accumulate with age and are tied to a higher risk of dementia, including Alzheimer's disease.
Madeline Ally, the study's lead author and a graduate researcher at the Department of Psychology, said that sleep is often studied as one overall measure rather than a collection of distinct patterns and habits, which can obscure how sleep relates to brain aging.
"Sleep is a universal but complex behavior, and there is still much to learn about how different aspects of sleep relate to brain health," Ally said.
For the study, participants completed a baseline questionnaire from 2006 to 2010 on five sleep behaviors: sleep duration, daytime napping, sleeplessness, unintentional daytime dozing and snoring. About nine years later, the same participants underwent brain MRI scans, which the researchers used to measure white matter lesion volumes. The study was conducted in collaboration with David Raichlen, the lead collaborator at the University of Southern California, and a professor of human and evolutionary biology.
All five behaviors were initially associated with greater lesion volume. But after the researchers accounted for related blood vessel health and lifestyle factors that can also affect the brain, such as high blood pressure, smoking and physical inactivity, three behaviors continued to stand out: sleeping outside the recommended range, frequent daytime napping and greater sleeplessness. Snoring and unintentional daytime dozing did not.
The findings on daytime napping were particularly interesting, since research shows short naps may also be helpful for alertness and cognition. Gene Alexander, the study's senior author and a professor in the Department of Psychology, said that the questionnaire did not capture details on the length or timing of individual naps. Future work will need to test whether shorter, occasional naps have different effects on the brain over time compared to longer, more frequent ones.
In a follow-up analysis, the researchers took a closer look at sleep duration and found that participants sleeping fewer than seven hours per night had increased lesion volume compared to those sleeping within the recommended range.
"Our findings suggest that having too little sleep may lead to greater white matter lesion volumes in the brain as we age," said Alexander. "We didn't see greater white matter impacts in people who reported longer sleep durations, but this needs to be followed up in cohorts with more long sleepers."
Nevertheless, Alexander said the three behaviors share a feature that makes them particularly important to study: each can be changed.
"Sleep is one of those potentially modifiable risk factors. If we can improve the quality of our sleep, it may help reduce the impacts of brain aging and maybe even lower the risk for dementias like Alzheimer's disease," Alexander said.
