By Anne Harding
Women plagued by sleep problems have more than triple the risk of developing the pain disorder fibromyalgia compared to their better-rested peers, a new study from Norway suggests.
The more often a woman experienced insomnia and other sleep problems, the more likely she was to have developed fibromyalgia 10 years later, according to the study, the largest to date to follow women who were initially free from chronic pain.
The findings imply that sleep problems may lead to fibromyalgia, but the researchers say the relationship isn't so clear-cut. Although sleep deprivation has been shown in previous research to increase inflammation and reduce the body's ability to manage pain, experts haven't been able to draw a straight line from sleep difficulties to fibromyalgia.
"Sleep problems are just one factor that may contribute to the development of fibromyalgia," says Paul J. Mork, Ph.D., a study coauthor and a researcher at the Norwegian University of Science and Technology, in Trondheim. "Fibromyalgia is a complex pain syndrome and there are numerous other factors that may contribute to the development of this illness."
Doctors have long been aware of the link between poor sleep and fibromyalgia, a chronic condition characterized by widespread pain and tender points in the soft tissues. Fibromyalgia patients -- more than 90 percent of whom are women -- nearly always report trouble sleeping, while poor sleep is in turn associated with worse pain. (A 1975 experiment found that depriving healthy volunteers of sleep caused them to develop fibromyalgia-like symptoms.)
"In the clinic we really do see a reciprocal relationship between fibromyalgia and sleep quality," says Lesley Arnold, Ph.D., a professor of psychiatry and behavioral neuroscience at the University of Cincinnati College of Medicine. "Pain can affect your sleep; it results in poor sleep for many patients, and that in turn increases the pain and results in the persistence of the problem."
The new study, which was published in the journal Arthritis & Rheumatism, included 12,350 women age 20 and older who had no fibromyalgia, muscle or bone pain, or other physical impairments when the study began, in the mid-1980s. When the researchers surveyed the women again, in the mid-1990s, roughly 3 percent reported that they had developed fibromyalgia.
At the study's outset, roughly two-thirds of the women said they had no difficulty sleeping. Compared with that group, those who said they "sometimes" had trouble falling asleep or had any sleep disorder during the previous month had double the risk of developing fibromyalgia. The risk was three and a half times greater among those who said they "often or always" had sleep problems.
The link appeared to be especially strong among women age 45 and older. Women in that age group who reported often or always having sleep problems had a more than fivefold increased risk of fibromyalgia compared to sound sleepers, while the corresponding risk among younger women was just three times greater.
The study has some key shortcomings. The researchers relied on the women's own assessment of their sleep problems and fibromyalgia symptoms, as opposed to official diagnoses. And though they took several potentially mitigating factors (such as body mass index, depression, and education levels) into account, they lacked data on anxiety, which has been linked to both sleep problems and fibromyalgia.
Other important factors that weren't measured in the study include menopausal status and a history of physical or psychological trauma, says Carol A. Landis, a professor at the University of Washington School of Nursing, in Seattle. As many as 30 percent to 50 percent of women with fibromyalgia report a history of trauma, Landis says.
Still, "The weight of the evidence really supports the important role of sleep in fibromyalgia," Arnold says. "We don't always understand what the biological mechanisms are underlying that association between sleep and pain, but clearly there's an important connection."
Doctors and patients should be aware of this connection and should address sleep problems -- especially unrefreshing sleep -- to lower the risk of the patient developing chronic pain, Arnold says.