Young, healthy men who were deprived of just a single night of sleep had elevated blood levels of tau, a protein that accumulates in the brains of those with Alzheimer’s disease and considered as one of the two main hallmarks of the disease. The study was small, and it’s unknown whether higher blood levels of tau translate to higher levels of the protein in the brain. But the findings add to a growing body of evidence linking poor sleep to brain health.
For the study, researchers in Sweden looked at 15 healthy men in their 20s. All said they regularly slept well for seven to nine hours a night.
For the first phase of the study, the young men spent two days and nights in a sleep lab, where they were allowed to get a good night of sleep for both nights.
For the second phase, the men again spent another two days and nights in the lab. They were allowed to sleep well during the first night. But on the second night they were kept awake the entire night. The lab lights stayed on while the study participants played games, watched movies and talked.
The researchers took blood samples each evening and morning. They found that after a good night of sleep, levels of tau rose by about 2 percent. But when sleep deprived, blood levels of tau rose by about 17 percent.
The researchers also looked at other biomarkers associated with Alzheimer’s, such as beta-amyloid, which can form the telltale brain plaques of the disease, but did not find changes in levels after a single night of sleep deprivation. The findings were published in Neurology, the medical journal of the American Academy of Neurology.
“Many of us experience sleep deprivation at some point in our lives due to jet lag, pulling an all-nighter to complete a project, or even doing shift work, working overnights or inconsistent hours,” said Dr. Jonathan Cedernaes, a study author and senior researcher at Uppsala University in Sweden. “Our exploratory study shows that even in young, healthy individuals, missing one night of sleep increases the level of tau in blood, suggesting that over time, such sleep deprivation could possibly have detrimental effects.”
In the last few years, due in part to the difficulty of finding successful therapeutic targets for beta-amyloid and related peptides, scientists are taking a renewed interest into the potential impact of tau in the onset and progression of Alzheimer’s disease. In the brain, inside the nerve cells/neurons, tau can undergo modifications and then stick to each other forming strands called neurofibrillary tangles. Tangles typically begin to form years before memory loss and other symptoms of Alzheimer’s disease become apparent.
Still, it’s uncertain what higher levels of tau in the blood, and what the form of tau measured in this study (total tau, and not the modified form of tau that is associated with Alzheimer’s) means for brain health. “It’s important to note that while higher levels of tau in the brain are not good, we do not know what higher levels of tau in blood represent,” Dr. Cedernaes said. “Higher levels in the blood may reflect that these tau proteins are being cleared from the brain, or they may reflect elevated tau levels in the brain.”
Indeed, it is possible that more tau in the blood is a good sign, an indication that tau is being expulsed from the brain. But it is also possible that a high level of tau in the blood correlates with more tau everywhere in the body, including in the brain, which would be a bad thing.
Earlier research suggests that sleep may serve a kind of housekeeping function, helping to clear the brain of tau and other toxins that can accumulate. Previous studies of older adults have suggested that sleep deprivation can increase the level of tau in the cerebral spinal fluid, which bathes the brain. Concussions and other head trauma can also increase circulating concentrations of tau in blood.
But plenty of people sleep poorly for years without experiencing memory loss or developing dementia. More research is needed into the role of poor sleep, tau accumulation in the blood stream and other factors in the onset of Alzheimer’s disease.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Christian Benedict, Kaj Blennow, Henrik Zetterberg, Jonathan Cedernaes: “Effects of acute sleep loss on diurnal plasma dynamics of CNS health biomarkers in young men.” Neurology, Jan. 8, 2020