There’s evidence in people and animals that short-term sleep deprivation can change the levels of amyloid-β, a peptide that can accumulate in the aging brain and cause Alzheimer’s disease. Scientists now show long-term consequences may also result from sustained poor sleep. In a study published September 3 in Current Biology, researchers found that healthy individuals with lower-quality sleep were more likely to have amyloid-β accumulation in the brain years later. The study could not say whether poor sleep caused amyloid-β accumulation or vice versa, but the authors say that sleep could be an indicator of present and future amyloid-β levels.
“Traditionally, sleep disruptions have been accepted as a symptom of Alzheimer’s disease,” says Ksenia Kastanenka, a neuroscientist at Massachusetts General Hospital who was not involved in the work. Her group showed in 2017 that improving sleep in a mouse model of Alzheimer’s disease, in which the animals’ slow wave sleep is disrupted as it usually is in people with the disease, halted disease progression.
Collectively, the results from these studies and others raise the possibility that “sleep rhythm disruptions are not an artifact of disease progression, but actually are active contributors, if not a cause,” she says, hinting at the prospect of using these sleep measures as a biomarker for Alzheimer’s disease.
As a graduate student at the University of California, Berkeley, Joseph Winer, who is now a postdoc at Stanford University, and his colleagues were interested in whether or not sleep could predict how the brain changes over time. They collaborated with the team behind the Berkeley Aging Cohort Study, which includes a group of 32 cognitively healthy adults averaging about 75 years of age. They participated in a sleep study, then had periodic cognitive assessments and between two and five positron emission tomography (PET) scans to check for the presence of amyloid-β in their brains for an average of about four years after the sleep study.
The researchers found at their baseline PET scan, which happened within six months of their sleep study, that 20 of the 32 participants already had some amyloid-β accumulation, which was not unexpected based on their average age. They also showed that both slow wave sleep, an indicator of depth of sleep, and sleep efficiency, the amount of time sleeping compared to time in bed, were both predictive of the rate of amyloid change several years later. In other words, people with lower levels of slow wave sleep and sleep efficiency were more likely to have faster amyloid build up.
The subjects all remained cognitively healthy over the duration of the study, says Winer. “We do expect that they’re at higher risk for developing Alzheimer’s in their lifetime because of the amyloid plaque.”
The strengths of the study include the well-characterized participants with detailed sleep assessments, as well as cognitive testing and longitudinal amyloid PET imaging, says Brendan Lucey, a sleep neurologist at Washington University in St. Louis who did not participate in the work.
There are still open questions about the link between sleep and amyloid deposition over time. “Amyloid accumulation on PET increases at different rates in amyloid-negative and amyloid-positive individuals, and even within amyloid-positive individuals,” Lucey explains. “Without adjusting for participants’ starting amyloid [levels], we don’t know if some participants would have been more likely to have increased amyloid compared to others, independent of sleep.”
“It is very hard to untangle this question of baselines,” acknowledges Winer. Because the sleep measures the team identified in the study are related to amyloid levels, to actually tease apart the effect of sleep quality on amyloid deposition and vice versa, it’d be necessary to study people starting as early as their fifties, when they’re much less likely to have amyloid accumulation, he says.
This study is “a great start,” David Holtzman, a neurologist and collaborator of Lucey at Washington University in St. Louis who did not participate in the work, tells The Scientist. In addition to controlling for the amount of amyloid deposition that is present in a subject’s brain at the beginning of the study, it would be important to see if the findings bear out in larger numbers of people and what role genetic factors play.
“The most important question down the road is to test the idea in some sort of a treatment paradigm,” Holtzman adds. “You can do something to improve the quality of sleep or increase slow wave sleep, and then determine if it actually slows down the onset of Alzheimer’s disease clinically.”
J.R. Winer et al., “Sleep disturbance forecasts β-amyloid accumulation across subsequent years,” Current Biology, doi:10.1016/j.cub.2020.08.017, 2020.