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Getting a recommended eight hours of sleep or more each night remains one of medicine's go-to suggestions for general health.
Sleeping those magical eight hours allows the body to recover, encourages better mental clarity, and gives the immune system time to heal.
But new data now suggests that trying to make up a lagging sleep schedule with cat naps could be detrimental.
A new study from Johns Hopkins University reports that people who are very sleepy during the day were three times more likely than those who were well-rested during the day to have a hallmark for Alzheimer's disease.
Connecting sleep to Alzheimer's disease
The new research contributes to an increasing body of evidence that a good night's sleep could be a factor in preventing Alzheimer's disease.
"Factors like diet, exercise and cognitive activity have been widely recognized as important potential targets for Alzheimer's disease prevention, but sleep hasn't quite risen to that status -- although that may well be changing," said Adam P. Spira, PhD. Spira also serves as an associate professor in the Department of Mental Health at the Johns Hopkins Bloomberg School of Public Health. Spira led the study with collaborators from the National Institute on Aging (NIA), the Bloomberg School and Johns Hopkins Medicine.
The study used data from the Baltimore Longitudinal Study of Aging (BLSA). This long-term study started in 1958 and followed thousands of volunteers as they aged.
The study periodically checked in with the participants by asking them yes or no questions. There were several questions in 1999 and 2000 that asked "Do you often become drowsy or fall asleep during the daytime when you wish to be awake?"
Another question asked if a participant napped and how often they took naps. Not only did the BLSA team ask these questions, but they also did other studies into neuroimaging of participants.
In 2005, some participants completed PET scans looking for beta-amyloid plaques in their brain tissue. Beta-amyloid plaques are often seen as a hallmark of Alzheimer's disease.
The Johns Hopkins team analyzed the data from those early scans to see if there was a connection between participants to reported to sleep during the daytime and whether they scored positive for a beta-amyloid deposit in their brans.
Before adjusting for factors associated with daytime sleepiness (i.e. age, education, BMI), the researchers noted those who reported daytime sleepiness were three times more likely to have the plaque deposition than those who didn't report it.
After adjusting for those common factors, it was still 2.75 times higher.
While the researchers aren't quite sure about the connection between lack of sleep/daytime naps and the amyloid-beta deposition, they have a few theories. It could be that disturbed or insufficient sleep causes the plaques to build up through an unknown mechanism in the body.
"However, we cannot rule out that amyloid plaques that were present at the time of sleep assessment caused the sleepiness," he added.
Further steps people can take
The researchers said further investigation needs to be done. Other animal studies seem to suggest that Alzheimer's consistently appears in sleep-deprived specimens.
"If disturbed sleep contributes to Alzheimer's disease," Spira added, "we may be able to treat patients with sleep issues to avoid these negative outcomes."
The study also noted it could be about more than just quantity but also the quality of sleep. Ultimately, one of the safest things people concerned with getting Alzheimer's disease can do is to get their recommended eight hours of uninterrupted sleep.
"There is no cure yet for Alzheimer's disease, so we have to do our best to prevent it. Even if a cure is developed, prevention strategies should be emphasized," Spira says. "Prioritizing sleep may be one way to help prevent or perhaps slow this condition."
The study was published in the journal SLEEP.