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.
