In Alzheimer's patients, sleep disruption can be especially severe and often results in nighttime confusion and wandering, according to the researchers.
The investigators analyzed data from the Rush Memory and Aging Project, which includes nearly 1,000 people who enrolled at age 65 and are being followed until death, at which point their brains are donated for research.
The results showed that elderly people and Alzheimer's patients have a substantial decline in what are called ventrolateral preoptic neurons, and that loss of these brain cells is associated with sleep problems.
"On average, a person in his 70s has about one hour less sleep per night than a person in his 20s," senior author Dr. Clifford Saper, chairman of neurology at Beth Israel Deaconess Medical Center in Boston, said in a medical center news release.
Sleep loss and fragmented sleep are associated with a number of health issues, including thinking and memory problems, 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," he noted.
The study was published online Aug. 20 in the journal Brain.
"These findings provide the first evidence that the ventrolateral preoptic nucleus in humans probably plays a key role in causing sleep, and functions in a similar way to other species that have been studied," Saper said.
The loss of these neurons with aging and with Alzheimer's disease may be a reason why older individuals often face sleep disruptions, he added. "These results may, therefore, lead to new methods to diminish sleep problems in the elderly and prevent sleep-deprivation-related cognitive [mental] decline in people with dementia," he concluded.
The U.S. National Library of Medicine has more about age-related changes in sleep.