People who continually have their sleep disrupted, whether by insomnia or a crying newborn, may become more susceptible to pain, preliminary research suggests.
In a sleep-lab study of 32 healthy young women, researchers found that those who were subjected to repeated sleep disruptions over three nights showed a change in their pain perception. Their bodies' ability to inhibit pain signals declined, and as a group, the women reported more "spontaneous" pain, such as an aching back or stomach cramps, on the days following their poor night's sleep.
In contrast, this was not the case for study participants who were allowed to sleep for only a few hours per night but did not have their sleep disrupted. Although these women slept for the same total time as those in the disrupted-sleep group, their pain perception appeared unaffected.
This suggests that repeated awakenings during the night might have a particular affect on the brain's processing of pain, the study authors report in the journal Sleep.
"It's not just the total sleep loss, it's the fragmentation," lead researcher Dr. Michael T. Smith, of Johns Hopkins University in Baltimore, told Reuters Health.
Specifically, he said, sleep disruptions may affect the body's opioid system, which helps regulate pain perception. In doing so, fragmented sleep might contribute to or worsen the chronic pain of people with fibromyalgia or lower back problems, for example.
The findings are based on a week-long sleep study of 32 healthy women. On the first two nights, all participants slept for a normal 8-hour period. They were then assigned to one of three groups for the next three nights: a "forced awakening" group where participants were repeated roused from sleep each night; a second group that was kept up late and awakened early; and a "control" group that continued to get a good night's sleep.
Throughout the study, the women also had their pain perception measured. In one test, pressure was applied to their arm muscles until they said they felt pain. In a second test, pressure was applied to each woman's arm while her opposite hand was immersed in cold water; normally, this cold-water shock should lessen the pain perceived in the other arm, as the body's pain-inhibiting systems kick in.
However, Smith's team found, this natural pain inhibition appeared to be dysfunctional when the study participants were subjected to forced awakenings. What's more, women in this group reported having more aches and pains on the days following their sleep-disrupted nights.
Smith said the study's forced-awakening condition was akin to having middle-of-the-night insomnia -- or to being a doctor on call or a parent responding to a newborn's cries.
People who have both chronic pain and trouble staying asleep should consider seeking therapy for their sleep problem, he suggested. One approach to treating insomnia, Smith noted, is to restrict the amount of time a patient sleeps; although this means at first sleeping for only a few hours, it's a solid, uninterrupted few hours.
So this type of therapy, by reducing fragmented sleep, might be helpful for people with chronic pain, according to Smith. "This study actually supports that approach, particularly for chronic pain patients," he said.
