There may be a new explanation as to why it gets harder to sleep as people get older. Research out of Harvard Medical School has found a link between age-related insomnia and the loss of neurons that “switch off” the brain.

The study, published in Brain, found a group of neurons that are responsible for blocking waking thoughts, thereby allowing a person to fall asleep. Researchers think that as a person ages, these neurons naturally break down, resulting in greater difficulties achieving and maintaining a restful sleep.

“The loss of these neurons with aging and with Alzheimer’s disease may be an important reason why older individuals often face sleep disruptions,” said lead author of the study, Professor Clifford Saper.

Saper added that someone in their 70’s gets an average of one hour less sleep per night than they did in their 20’s.

Sleep disturbances of this nature have been associated with other health problems, like high blood pressure, cardiovascular disease, impaired cognition, and increased risk of type 2 diabetes, Saper said. He thinks it is possible that these neurons affect all different types of health concerns that develop with age, including Alzheimer’s.

Researchers first identified the cluster of neurons in rats. Known as the ventrolateral preoptic nucleus, the group appeared to serve an integral part in regulating sleep. Rats who had this portion of the brain inhibited were reported to sleep about 50 percent less than those with normal brain function.

Data was then analyzed using brains donated by 45 elderly people who also agreed to wear sleep monitors starting at the age of 65 until their deaths. A very similar area of the brain as was found in rats was identified in humans.

Those who participated but had the least intact neurons in this area were shown to sleep restfully less than 40 percent of the time.