By comparing the spinal fluid against self-reported sleep problems, Bendlin and her colleagues found that the subjects who had sleep issues were more likely to show evidence of tau pathology, brain cell damage and inflammation, even when other factors like depression, body mass, cardiovascular disease and sleep medications were taken into account.
"Our findings align with the idea that worse sleep may contribute to the accumulation of Alzheimer's-related proteins in the brain," Bendlin said. "The fact that we can find these effects in people who are cognitively healthy and close to middle age suggest that these relationships appear early, perhaps providing a window of opportunity for intervention."
That's important, Bendlin added, because delaying the onset of Alzheimer's in those at risk by a mere five years "could reduce the number of cases we see in the next 30 years by 5.7 million and save $367 billion in health care spending."
"Another new finding in this study is that daytime sleepiness, and not just disrupted nighttime sleep, is associated with early changes of Alzheimer's disease," said Dr. Yo-El Ju, an assistant professor of neurology at Washington University's
Sleep Medicine Center.
Ju also studies the association between sleep and dementia, and she co-wrote an accompanying editorial
for the new study.
"Overall, this study confirms the relationship between early Alzheimer's disease and sleep disturbance," Ju said, "and (it) expands -- in terms of both time and symptoms -- the window in which sleep-wake problems can be assessed for and treated, with the hope of reducing the risk of dementia due to Alzheimer's disease."
One of the limitations of the study was that the sleep problems were self-reported. Bendlin and her colleagues are recruiting people at risk for Alzheimer's to be studied in a sleep lab, where objective measurements can be taken.
"If it turns out to be the case that an intervention which improves sleep also results in less amyloid being deposited in the brain, that would provide strong support for implementing interventions before people start to show cognitive decline associated with Alzheimer's disease," she said.
Dr. Rudolph Tanzi, who directs the genetics and aging research unit at Massachusetts General Hospital, agreed.
"Increasing amounts of evidence indicate that getting at least seven to eight hours of sleep is essential for brain health and function," Tanzi said. "In the deepest stage of sleep, the brain cleans itself out of plaque and other toxic materials that trigger Alzheimer's disease. This reduces brain inflammation and is entirely consistent with this exciting new study."
Which problem came first?
Not everyone with sleep problems in the study had abnormalities in their spinal fluid. For example, those with obstructive sleep apnea showed no association. Bendlin stresses that much remains to be discovered about the link between sleep and dementia.
"Not everyone who experiences sleep problems should now worry about developing dementia due to Alzheimer's disease," she said, adding that there is not yet a clear cause and effect relationship.
"Animal studies suggest sleep affects development of brain changes, but brain changes in turn also affect sleep," Bendlin said. "In terms of figuring out which comes first, brain changes or sleep problems, that will be difficult to tease apart, because the effects really do appear to be going in both directions."
"In experimental studies, there does seems to be evidence of both chicken and egg," said neuroscientist Jeffrey Iliff of Oregon Health and Sciences University. "You can drive it either direction. So there may be a bio-directional interaction."
That's good news if true, he said, because it means we have may have some control over whether we develop dementia.
"No, the public can't remove amyloid plaque," Iliff said. "But if sleep disruption is promoting this process, then improving sleep is half of the solution to slowing the process of dementia as it develops over one's life."
Keith Fargo, director of scientific programs and outreach for the Alzheimer's Association, agreed: "This new study suggests there may be an opportunity to improve cognition and possibly reduce dementia risk through early diagnosis and effective treatment of sleep disorders."