Chronic sleep problems can inflame a number of health problems, from widespread pain to speeding up cancer. Though sleep disturbances have been observed in people with Alzheimer's disease, whether this is a cause or effect has been unknown. Now, researchers say individuals with chronic sleep disruptions could face earlier onset of Alzheimer's.
The researchers, from Temple University in Philadelphia, PA, have published the results of their pre-clinical study in the journal Neurobiology of Aging.
As a start, the team focused on longitudinal studies that showed individuals who reported chronic sleep problems often develop Alzheimer's disease.
Sleep disturbances can be caused by a number of factors, including work, stress, insomnia or other factors. According to the Centers for Disease Control and Prevention (CDC), insufficient sleep is associated with chronic conditions and diseases, such as diabetes, cardiovascular disease, obesity and depression.
"The big biological question that we tried to address in this study is whether sleep disturbance is a risk factor to develop Alzheimer's or is it something that manifests with the disease," says lead author Domenico Praticò, professor of pharmacology and microbiology/immunology in the university's School of Medicine.
Sleep-deprived mice exhibited impaired learning and memory
To further investigate, Praticò and his team employed the use of a transgenic Alzheimer's mouse model - mice with DNA from humans - that began developing learning and memory problems within 1 year, which is the equivalent of a human who is around 50 or 60 years old.
Mice who were deprived of sleep showed "significant impairment" in learning and memory, compared with the mice who slept normally.
By the time the mice were 14-15 months old, they had typical Alzheimer's brain pathology, which included amyloid plaques and tau protein tangles. The researchers explain these are the two major brain signatures for the disease.
When the mice were 6 months old (the equivalent of a 40-year-old human), the researchers began their 8-week study.
While one group of mice was exposed to 12 hours of light and 12 hours of darkness, another group was exposed to 20 hours of light and 4 hours of darkness, which significantly reduced their sleep time.
Praticò says that at the end of the study period, they did not observe anything vastly different between the two groups.
But when they conducted memory tests in the mice, the group with reduced sleep time "demonstrated significant impairment in the working and retention memory, as well as their learning ability," he says.
After the team examined the brains of the mice, they did not observe a difference in amyloid plaques, but Praticò says:
"However, we did observe that the sleep disturbance group had a significant increase in the amount of tau protein that became phosphorylated and formed the tangles inside the brain's neuronal cells."
Disruption in synaptic connection impairs brain
Praticò explains that elevated levels of phosphorylated tau can disrupt the synaptic connection of cells or the ability to transport nutrients or chemicals, or transmit electrical signals from cell to cell.
Fast facts about sleep problems
- Over one quarter of the US population report not getting enough sleep.
- Nearly 10% experience chronic insomnia.
- Sufficient sleep is regarded as a "vital sign" of good health.
Tau protein is an important part of neuronal cell health, so these elevated levels cause a disturbance in normal function.
"Because of the tau's abnormal phosphorylation," Praticò says, "the sleep-deprived mice had a huge disruption of this synaptic connection. This disruption will eventually impair the brain's ability for learning, forming new memory and other cognitive functions, and contributes to Alzheimer's disease."
Since the sleep-deprived mice developed this Alzheimer's brain pathology before the mice that had normal sleep, the team says sleep disturbances act as a trigger, accelerating these pathological processes and damaging the synaptic connection.
"We conclude from this study that chronic sleep disturbance is an environmental risk factor for Alzheimer's disease," Praticò says. "But the good news is that sleep disturbances can be easily treated, which would hopefully reduce the Alzheimer's risk."
The team says correcting sleep disorders could be a "viable therapeutic strategy" to prevent or slow progression of Alzheimer's disease in people at risk.
Medical News Today recently reported on a study that suggested Alzheimer's, which is the sixth leading cause of death in the US, actually contributes to as many deaths as the top two. The study authors said this means there is incorrect identification of the disease as the actual reason for death.