Association of chronic pain and fibromyalgia with cardiovascular risk factors and metabolic syndrome: the Norwegian HUNT study
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Background: Chronic pain is a common condition, affecting a high percentage of the population. Fibromyalgia (FM) is a syndrome characterized by chronic widespread pain, fatigue and tenderness at specific anatomical locations (tender points), which affects more women than men. Chronic widespread pain has recently been associated with increased risk of mortality, and especially to death from cancer and cardiovascular diseases. The aim of this study was to explore if people who reported chronic pain or FM had more unfavourable levels of cardiovascular risk factors compared to people without pain, and thus a higher prevalence of metabolic syndrome. The effect of number of pain sites and physical activity level was also explored. Methods: The study was based on cross-sectional data from 53 469 persons, 25 392 men and 28 077 women, who participated in the Nord-Trøndelag Health Study from 1995 to 1997 (HUNT 2). Levels of cardiovascular risk factors were compared using linear regression, and OR for metabolic syndrome (defined by the ATP III criteria) and the various components were calculated by logistic regression. Results: Men and women with chronic pain and FM had higher waist circumference, body mass index, and triglyceride level, and lower high-density lipoprotein cholesterol compared to those with no pain. Lower values on both systolic and diastolic blood pressure were observed in the pain groups. The odds ratio (OR) for metabolic syndrome among those with chronic pain was 1.05 (95 % confidence interval, 0.98-1.12) in men and 1.18 (1.10-1.26) in women, and among those with FM it was 1.53 (1.14-2.04) in men and 1.66 (1.47-1.88) in women. There was a dose-response association between number of pain sites and the continuous measures of all outcome variables (all p-trends <0.01), except glucose (p-trend= 0.437 for men and 0.209 for women). Physically active persons had more favourable levels on most variables compared to the inactive within each pain group. The combination of FM and inactivity showed the strongest association with metabolic syndrome, with an OR of 2.05 (1.29-3.27) in men and 2.34 (1.95-2.81) in women. Conclusion: In this population-based study, the prevalence of metabolic syndrome was higher among women with chronic pain, and among men and women with FM, compared to people without pain. There was a dose-response association between number of pain sites and metabolic syndrome and its components. Physical activity modified some of the observed association between chronic pain/FM and cardiovascular risk factors, resulting in more favourable risk factor levels.