The incidence and prevalence of Chronic Fatigue Syndrome, Back Pain of unknown origin, Fibromyalgia, and Myalgia in Norwegian women, and their association to physical activity. A prospective cohort study of material from the Norwegian Women and Cancer (NOWAC) study.

Abstract

Background: Musculoskeletal disorders (MSDs) appear relatively frequent and are costly for society each year, yet they are poorly understood. Four commonly occurring MSDs are Chronic Fatigue Syndrome (CFS), Back Pain (BP) of unknown origin, Fibromyalgia (FM), and muscle pain/Myalgia. There are few Norwegian epidemiologic data on these four outcomes. Physical activity (PA) has been internationally recognized as having a protective effect against chronic disease. The association between PA and these four outcomes is not well understood and the main aim of this study was to investigate this relationship in a large prospective cohort of Norwegian women. Methods: Self-reported data were gathered from 76 367 women in the nationally representative cohort study the Norwegian Women and Cancer study. Data were gathered on total amount of PA at enrolment and of the four outcome conditions during follow-up, in addition to covariate information. We calculated incidence rate and total prevalence. The association between PA and the four outcomes was assessed using multivariate logistic regression analysis. Prevalent cases were excluded from logistic regression analysis. PA was assessed for trend and as a categorical variable. Results: Incidence densities per 100 000 person years were calculated to be as follows: CFS 411, BP 1268, FM 287, and myalgia 1509. Total prevalence was found to be 2.58% for CFS, 13.65% for BP, 5.02% for FM, and 17.87% for myalgia. These were comparable to age-standardized rates for the corresponding Norwegian female population. There was a significant trend (p < 0.001) that increasing levels of PA were associated with a reduced risk CFS, BP and FM. Compared to moderate PA level, very low levels of PA was significantly associated with increased risk of CFS (OR 1.61 (CI 1.38-1.88)), BP (OR 1.17(CI 1.04-1.31)), and FM (OR 1.30(CI 1.07-1.58)). For CFS, PA levels low (OR 1.31 (CI 1.19-1.44)) and very high (OR 1.18 (CI 1.01-1.38)) were also associated with an increased risk of PA. The results showed no significant associations between PA and mylagia. Conclusion: Our study found nationally representative data for incidence and prevalence of CFS, BP, FM, and myalgia in Norwegian women. When compared to moderate levels of total PA, very low PA was associated with an increased risk of CFS, BP, and FM. Low and very high levels of PA were associated with an increased risk of CFS. More studies are needed to confirm the incidence for these outcomes in the Norwegian population, and to investigate the association between these and different types of PA.