When tau proteins clump together to form tangles, they injure nearby tissues in the brain. If allowed to accumulate, these tangles can cause brain damage that could result in any of the forms of dementia.
The results of the study suggest that sleep deprivation can lead to Alzheimer's disease. Conversely, good sleep habits could protect the brain from damage.
In an earlier study, researchers from the Washington University School of Medicine in St. Louis (WUSM) reported that older people who did not sleep well had higher levels of this protein. But that study failed to determine if the lack of sleep directly increased tau levels.
Hence, researchers conducted a new experiment on mice and people. They evaluated tau levels in the brains of mice and people who enjoyed normal sleep and those who suffered from sleep deprivation. (Related: Anticholinergic drugs may be increasing your risk of dementia.)
Lack of sleep increases the amount of dangerous tau protein in the brain
Mice are awake during the night and sleep throughout the day. The WUSM researchers noted that tau levels in their brains were twice as high at night than during the day. However, when their sleep was disrupted during day, their tau levels also doubled.
Similar results were obtained from the analysis of cerebrospinal fluid taken from people after a good night's sleep and after their sleep got disrupted. The researchers reported that a sleepless night increased tau levels by half in humans.
Sleep deprivation causes stress and unhappiness in people. If they don't get ample sleep, people would usually sleep in as soon as they get the chance to do so. Similarly, mice that got woken up rebounded from a sleepless day and tried to make up for the loss of sleep.
The researchers' next step was to determine if behavioral changes or stress were responsible for the increase in tau levels. They set up a mice model that could be forced to stay awake for long periods of time. They confirmed that staying awake for extended periods increased tau levels in the mice.
The researchers concluded that tau is produced when brain activity is high during waking hours. Then, it is cleared away during sleep. Lack of sleep, however, disrupts this clearing process, allowing tau to accumulate into dangerous tangles that could eventually harm the brain.
Good sleeping habits can protect the brain from Alzheimer's disease
In patients with Alzheimer's disease, tau tangles often appear in brain regions involved with memory, reported a study. As tau tangles increase and spread, the patients' ability to think clearly declines.
In a similar experiment, researchers put tau tangles in the hippocampi of mice. They forced some of these mice to stay awake for prolonged periods and allowed the others to sleep normally.
After four weeks, they found that the brains of sleep-deprived mice had far more tau tangles than the mice that got enough rest. Furthermore, the new tangles were found in the same brain regions that were affected in patients with Alzheimer's disease.
"Getting a good night's sleep is something we should all try to do," said David Holtzman, the main author of the study. "Our brains need time to recover from the stresses of the day."
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