A new research explains why elderly people have difficulty sleeping.

Researchers at Beth Israel Deaconess Medical Center and University of Toronto assessed the relationship between aging and less sleep. Their results showed that sleeping problems might be because of loss of brain cells.

"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 press release.

For the study, the researchers examined data collected from the Rush Memory and Aging Project. At least 1,000 elderly people were involved in the study and all were 65-years-old at the time of enrollment back in 1997. As a part of their study, the elderly participants were followed till  their death and some donated their brains for research. The seniors agreed to wear small devices on their wrists for seven to 10 days every two years. The device tracked their movements.

Researchers concentrated on 45 brains and found that older people and Alzheimer's patients experience a significant decline in their ventrolateral preoptic neurons. Alzheimer's patients lose these neurons at a faster rate. The ventrolateral preoptic neurons are responsible for regulating sleep patterns. The researchers stated they believe that when these neurons die due to old age, sleeping problems arise.

"We found that in the older patients who did not have Alzheimer's disease, the number of ventrolateral preoptic neurons correlated inversely with the amount of sleep fragmentation," says Saper. "The fewer the neurons, the more fragmented the sleep became."

He added, "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. It now appears that loss of these neurons may be contributing to these various disorders as people age."

The study, 'Sleep is related to neuron numbers in the ventrolateral preoptic/intermediate nucleus in older adults with and without Alzheimer's disease,' was published in the journal, Brain.