Being overweight or obese is associated with a woman's higher risk of developing fibromyalgia, as is lack of exercise, according to findings from a team of researchers in Norway.
While frequent exercise may have analgesic effects of varying duration, the relationship between exercise and fibromyalgia remains unclear, investigators at the Norwegian University of Science and Technology in Trondheim said. “Regular physical exercise, and thereby improved physical fitness, may serve as a buffer against the perpetuation of musculoskeletal symptoms that eventually lead to the development of [fibromyalgia],” they hypothesized. “However, the results of this study do not indicate a strong effect of physical exercise” on development of the disorder.
Links between obesity and fibromyalgia have been described in previous studies, lead investigator Paul. J. Mork, Ph.D., and colleagues noted, though the reasons for such associations are as yet not well understood. Fibromyalgia and obesity share some known characteristics, such as elevated serum levels of certain proinflammatory cytokines, they said, and dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis.
For their study, published online ahead of print in the journal Arthritis Care and Research (doi: 10.1002/acr.20118), investigators used data from the Nord-Trndelag Health (HUNT) Study, a two-part, government-sponsored cohort first conducted between 1984 and 1986, and again in a follow-up between 1995 and 1997.
After excluding from the cohort women who had been ill at baseline or who had not supplied enough relevant information in study questionnaires, the researchers identified 15,990 women 20 years and older who initially reported no fibromyalgia or physical impairment. Of these, 380 reported physician-diagnosed fibromyalgia 11 years later during the follow-up part of the study. Each study phase included a series of physical examinations and measurements along with detailed self-reported questionnaires. At the time of follow-up, the study comprised 9,942 normal weight, 4,245 overweight, and 1,481 obese women.
The purpose of the study was “to investigate whether an inverse association exists between the level of leisure time physical exercise and the future development of [fibromyalgia] in a large unselected population of women,” Dr. Mork and colleagues wrote, and, separately, whether high body mass index contributed to the development of the disease.
Overall, women who reported that they exercised 4 or more times per week were 29% less likely to develop fibromyalgia than women who described themselves as inactive. Obese women (BMI of at least 30 kg/m
Among overweight and obese women (defined as any with a BMI of at least 25 kg/m
Among the study's limitations, the authors pointed out, was the fact that information about exercise habits was self-reported, not particularly detailed as to the type or intensity of activity, and not followed up in the second part of the cohort. Another limitation noted by the authors was that because participation in follow-up was voluntary, women with high BMI or sedentary lifestyles at baseline may have chosen not to participate in follow-up, making the actual relative risk higher than the study reflected.
Also, the large number of unknowns in the pathogenesis of fibromyalgia increased the potential for confounding, they acknowledged. “[G]enetic predisposition, sociopsychological factors, adverse life events and occupational exposures (eg., work stress), could be of importance,” they wrote, but none of these was included in their analysis.