Study Examines Link Between Aging and Sleep Disruption

Loss of neurons in the brain may impair the ability to fall and stay asleep.

Like the sprouting of grey hair or the onset of joint pain, disrupted sleep is yet another common sign that we’re getting older every day. Now, research from Harvard Medical School (HMS), Beth Israel Deaconess Medical Center, and the University of Toronto may explain way.

According to a new study published online in the neurology journal, Brain, the elderly and those with Alzheimer’s disease have significantly fewer inhibitory neurons, the loss of which results in sleep disruption.

Clifford Saper, the study’s senior author, said in an HMS report that people in their 70s typically get about an hour less sleep per night than people in their 20s.

“Sleep loss and sleep fragmentation is associated with a number of health issues, including cognitive dysfunction, increased blood pressure and vascular disease, and a tendency to develop type 2 diabetes,” Saper said. “It now appears that loss of these neurons may be contributing to these various disorders as people age.”

Previous studies with rats suggested that a specific group of neurons known as the ventrolateral preoptic nucleus facilitated sleep by inhibiting arousal systems in the brain. Researchers hypothesized that the intermediate nucleus, a group of neurons found in the human brain, plays a similar role in regulating sleep-wake cycles in humans. According to the report:

In order to test this hypothesis, the investigators analyzed data from the Rush Memory and Aging Project, a community-based study of aging and dementia which began in 1997 and has been following a group of almost 1,000 subjects who entered the study as healthy 65-year-olds and are followed until their deaths, at which point their brains are donated for research.

The authors examined the brains of 45 study subjects (median age at death, 89.2), identifying ventrolateral preoptic neurons by staining the brains for the neurotransmitter galanin. They then correlated the actigraphic rest-activity behavior of the 45 individuals in the year prior to their deaths with the number of remaining ventrolateral preoptic neurons at autopsy.

The study revealed that having fewer neurons resulted in higher rates of sleep disruption. It also showed a correlation between lost neurons and sleep impairment in Alzheimer’s patients.

“The loss of these neurons with aging and with Alzheimer’s disease may be an important reason why older individuals often face sleep disruptions,” Saper said in the report. “These results may, therefore, lead to new methods to diminish sleep problems in the elderly and prevent sleep-deprivation-related cognitive decline in people with dementia.”

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