Association between physical exercise, body mass index, and risk of fibromyalgia: longitudinal data from the Norwegian Nord-Trøndelag Health Study.

OBJECTIVE: To examine the association between leisure time physical exercise, body mass index (BMI), and risk of fibromyalgia (FM).

METHODS: A longitudinal study with baseline assessment of physical exercise (frequency, duration, and intensity) and BMI was used to explore the risk of having FM at 11-year followup in a large, unselected female population (n = 15,990) without FM or physical impairments at baseline.

RESULTS: At followup, 380 cases of incident FM were reported. A weak dose-response association was found between level of physical exercise and risk of FM (for trend, P = 0.13) where women who reported the highest exercise level had a relative risk (RR) of 0.77 (95% confidence interval [95% CI] 0.55-1.07). BMI was an independent risk factor for FM (for trend, P < 0.001), and overweight or obese women (BMI > or =25.0 kg/m(2)) had a 60-70% higher risk compared with women with normal weight (BMI 18.5-24.9 kg/m(2)). Overweight or obese women who exercised > or =1 hour per week had an RR of 1.72 (95% CI 1.07-2.76) compared with normal-weight women with a similar activity level, whereas the risk was >2-fold higher for overweight or obese women who were either inactive (RR 2.09, 95% CI 1.36-3.21) or exercised <1 hour per week (RR 2.19, 95% CI 1.39-3.46).

CONCLUSION: Being overweight or obese was associated with an increased risk of FM, especially among women who also reported low levels of physical exercise. Community-based measures aimed at reducing the incidence of FM should emphasize the importance of regular exercise and the maintenance of normal body weight.