The researchers initially looked at longitudinal studies that showed that people who reported chronic sleep disturbances were more likely to develop Alzheimer’s disease.
The researchers used Alzheimer’s mice models in which the rodents developed memory problems within one year.
The eight-week study involved mice when they were six months old – analogous to human mid-40s. The mice in on group were on a schedule to receive 12 hours of light and 12 hours of darkness, while the second group received 20 hours of light and only four hours of darkness, which meant reduced amount of sleep.
“At the end of the eight weeks, we didn’t initially observe anything that was obviously different between the two groups. However, when we tested the mice for memory, the group which had the reduced sleep demonstrated significant impairment in their working and retention memory, as well as their learning ability,” explained Praticὸ.
“Surprisingly, we didn’t see any difference between the two groups in the amyloid plaques. 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,” he added.
Elevated levels of phosphorylated tau can disrupt the cells’ synaptic connection or their ability to transport a nutrient/chemical or transmit an electrical signal from one cell to another.
“Because of the tau’s abnormal phosphorylation, 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,” Praticὸ continued.
Sleep deprivation was found to speed up Alzheimer’s pathology, which means that sleep deprivation may act as a trigger of tau phosphorylation.
The researchers concluded that sleep disturbances are an environmental risk factor for Alzheimer’s disease.
Self-reported sleep disturbances linked to higher Alzheimer’s disease risk in men
An alternative study found that self-reported sleep disturbances are linked to higher Alzheimer’s disease risk in men. The researchers followed over 1,000 men. Study lead and sleep researcher Christian Benedict explained, “We demonstrate that men with self-reported sleep disturbances run a 1.5-fold higher risk to develop Alzheimer’s disease than those without reports of sleep disturbances during a 40-year follow-up period. The later the self-reported sleep disturbance was found, the higher the risk was for developing Alzheimer’s disease. These findings suggest that strategies aimed at improving sleep quality in late life may help reduce the risk to develop Alzheimer’s disease.”
“Importantly, there are several lifestyle factors, such as exercise, that can influence your brain’s health. Thus, it must be borne in mind that a multifaceted lifestyle approach comprising good sleep habits is essential for maintaining brain health as you age,” Benedict added.
In his earlier research, Benedict found that a single night of sleep deprivation increased blood concentration of molecules that can contribute to acute brain damage.
Shorter sleep duration and poorer sleep quality linked to Alzheimer’s disease progression
In a cross-sectional study of 70 men, the researchers aimed to determine if there is an association between self-reported sleep disturbances and beta-amyloid deposition.
The researchers found that shorter sleep duration and poorer sleep quality were linked to a greater Alzheimer’s disease progression. Additional research is required to determine whether sleep disturbances are a cause or an accelerator of Alzheimer’s disease.