What exactly causes these changes?
The truth is that no one knows for sure. “We’re only just starting to understand why all of this happens,” said Luis de Lecea, a professor of psychiatry and behavioral sciences at Stanford University.
One explanation might have to do with an aging brain. In a study published in February, Dr. de Lecea and his team found that a particular cluster of neurons responsible for wakefulness became overly stimulated in aging mice, disrupting their sleep cycles. This shift “likely also happens to humans,” he said, because the part of the brain that regulates sleep in mice, called the hypothalamus, is similar to that of humans. (Many sleep studies are conducted in mice for practical and ethical reasons.) Researchers have also found that the suprachiasmatic nucleus, another brain region that regulates the body’s circadian rhythms, deteriorates in mice with age. This results in sleep disorders, including trouble falling asleep at regular times.
Certain lifestyle changes can lead to sleep disruption later in life, too, said Adam Spira, a professor and sleep researcher at the Johns Hopkins Bloomberg School of Public Health. As people retire, their days become less structured and routine. They may wake up later or nap during the day, which can make it harder to fall asleep at night, creating a vicious cycle.
Researchers have also found links between depression, loneliness, grief over the loss of a loved one and poor sleep in older adults. And in a 2014 study, Dr. Spira concluded that older adults who struggled with certain activities or household chores, like laundry, grocery shopping, meeting with friends or taking a walk, were more likely to report insomnia symptoms than older adults who were able to participate in those activities.
For women, hot flashes, night sweats and higher rates of depression, anxiety and stress — common symptoms of the menopausal transition — are also correlated with poor sleep. But researchers are still not exactly sure why those perimenopausal symptoms might be more severe and frequent in some women, and how best to address them.
