The connection between sleep deprivation and various degenerative diseases has long been suspected but has remained hard to prove. However, we now have evidence that even one night without sleep may increase susceptibility to Alzheimer's disease, which if confirmed would make lack of sleep a true health crisis.
Alzheimer's disease, by far the most common cause of dementia, is identified from the plaques of the beta-amyloid peptide in the brain. Although debate continues to rage among neuroscientists as to the extent the plaques cause damage to the brain, rather than being a symptom of it, there is little doubt excess beta-amyloid is a bad sign.
A team at the National Institute of Alcohol Abuse and Alcoholism, Maryland, diverged from the name of their institution to use positron emission tomography and the radiotracer 18F-florbetaben to measure beta-amyloid levels in 20 healthy people in their 30s and 40s. 18F-florbetaben binds to beta-amyloid, particularly in its insoluble plaque form, allowing us to map its presence in the brain.
Participants were tested after a good night's sleep and then again after 30 hours of wakefulness. In Proceedings of the National Academy of Sciences, the researchers announced an average 5 percent increase in amyloid-beta in the right hippocampus and thalamus of the brain. Nineteen of the participants had more beta-amyloid after sleep deprivation, in one case by 16 percent. These brain areas are associated with short-term memory and sorting of sensory information respectively, and the hippocampus is among the first regions to be affected by Alzheimer's disease.
To absolutely no one's surprise, participants' mood worsened after a sleepless night, but it may be significant that the extent to which this occurred correlated with an individual's increase in beta-amyloid in these brain regions.
Previous studies have indicated beta-amyloid is a waste product of the brain during wakefulness and is cleared during sleep. We've also observed increased concentrations of the peptide in sleep-deprived rodents. Nevertheless, a detectable increase after just one night is more powerful evidence for a connection than we might have expected to find.
If a good night's sleep normally clears beta-amyloid buildup from the brain, we might ask whether just one night's sleep in a healthy person is sufficient to clear the backlog? Perhaps for most people, a period of sleep deprivation does not matter for Alzheimer's, and dementia only awaits those whose brain-cleansing mechanisms are malfunctioning for other reasons. On the other hand, it's entirely possible that even for those with a normal capacity to remove beta-amyloid, too long without sleep eventually overwhelms the body's cleaning mechanisms.
We need further research to find out, but in the meantime, avoiding Alzheimer's sounds like a good excuse if you overslept and arrived late for work.