In individuals with Alzheimer's disease, this common and troubling symptom of aging tends to be especially pronounced, often leading to nighttime confusion and wandering.

Now, a study led by helps explain why sleep becomes more fragmented with age. Reported online today
 

In a new study published in the journal Brain, researchers at Beth Israel Deaconess Medical Center and the University of Toronto/Sunnybrook Health Sciences Center demonstrated for the first time that a group of neurons, whose loss leads to sleep disruption, are substantially diminished among the elderly and individuals with Alzheimer’s disease.
 

“On average, a person in his 70s has about one hour less sleep per night than a person in his 20s,” explained Clifford B. Saper, M.D., chairman of neurology at Beth Israel and a professor at Harvard Medical School. "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.
 

“It now appears that loss of these neurons may be contributing to these various disorders as people age.”
 

Eight years ago, Dr. Saper’s lab first discovered that the brain cells in question functioning as a “sleep switch” in rats, allowing the animals to fall asleep. The new research found a group of cells in the human brain is located in a similar location and has the same effect in seniors.
 

The investigators analyzed data from the Rush Memory and Aging Project, a study of aging and dementia that began in 1997 involving almost 1,000 subjects were followed until their deaths, at which point their brains are donated for research.
 

The researchers examined the brains of 45 study participants to identify the “sleep switch” cells.
 

“We found that in the older patients who did not have Alzheimer's disease … the fewer the neurons, the more fragmented the sleep became,” Dr. Saper said.
 

“These findings provide the first evidence that the [these cells] in humans probably [play] a key role in causing sleep, and functions in a similar way to other species that have been studied,” said Dr. Saper.

“The loss of these neurons with aging and with Alzheimer's disease may be an important reason why older individuals often face sleep disruptions. 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.”