Alzheimer's Linked to Chronic Sleep Loss
Chronic sleep loss can lead to brain cell loss and may contribute to the development of Alzheimer's disease, according to a new experimental study published in the September 24 issue of the journal Science.
Patients with Alzheimer’s disease are known to suffer from sleep abnormalities, but past researchers have been unclear to which came first – the chronic sleep deprivation or the disease progression and resulting brain damage.
In the study performed at the Barnes-Jewish Hospital in St. Louis, laboratory mice were given a shot of a hormone called orexin, which promotes wakefulness. The test mice were only allowed four hours of sleep each day, while the control group was allowed to sleep normally. Over a period of three weeks, the mice that were sleep-deprived had 25% more brain plaques than the mice that were well rested.
The researchers also studied human subjects and found a similar pattern in a small sample group of 10 healthy people.
Levels of a protein called amyloid-beta increase in the hippocampus region of the brain and in the spinal fluid during the waking hours and decrease during sleep. Having longer periods of wakefulness, such as in insomnia, cause the levels of amyloid-beta to increase at an accelerated rate. These proteins can become sticky and clump together, forming the plaques seen in the brains of patients with Alzheimer’s disease. These plaques eventually lead to the death of neurons and cause the symptoms of memory loss and disorientation.
Sleep apnea is one condition that leads to sleep deprivation. Patients with sleep apnea experience frequent episodes of breathing disruptions during the night. With each apnea event, the brain briefly causes the patient to awaken so that they resume breathing. Some studies have indicated that as many of 90% of Alzheimer’s patients may suffer from sleep apnea. Treatment with CPAP to regulate breathing patterns has been shown to slow the rate of cognitive decline.
Narcolepsy is another sleep disorder that causes daytime sleepiness. Research has found that patients with the disease have low levels of orexin. Scientists are in clinical trials with a new drug called Almorexant that interrupts the body’s production of orexin to treat patients with chronic insomnia and other sleep disorders.
Neuroscientist Damian Crowther of the University of Cambridge discourages the use of sleeping pills for Alzheimer’s patients until a better link can be established between chronic sleep deprivation and dementia diseases. He instead encourages more natural methods, such as exercise, to induce sound sleep.
Approximately 5.3 million people are living with Alzheimer’s in the United States, according to the Alzheimer’s Association advocacy group. There is currently no cure for the disease.
Sources: Science DOI: 10.1126/science.1180962, The National Institutes of Health Clinical Trials, and The American Sleep Apnea Association.