title: Individual and joint effects of risk factors for onset widespread pain and obesity - a population-based prospective cohort study.
abstract: Widespread musculoskeletal pain (WSP) and obesity frequently co-occur and may have shared risk factors. We aimed to investigate whether four dichotomized risk factors individually or jointly increase the risk for the onset of WSP and onset of obesity.
  
  
  
  Persons aged 34-76 years in 2004 living in Ullensaker municipality, Norway, responded to questionnaires in 2004 and 2010 (n = 1553). Using causal interaction analyses, we examined whether baseline obesity and WSP, poor sleep quality, mental distress and poor physical fitness jointly increased the risk of new onset WSP (≥3 pain sites leading to disability the last year) and new onset obesity (self-reported BMI ≥30 kg/m(2) ) in persons without WSP (n = 1270) or without obesity (n = 1300) at baseline respectively.
  
  
  
  The mean (SD) age was 51 (12.1) years and 56% were female. The incidence of WSP and obesity were 9.1% and 5.4%. Mental distress and poor sleep quality individually and jointly with poor physical fitness increased WSP onset risk (relative excess risk due to interaction [RERI] = 1.90, 95% CI, 0.39-3.42 and RERI = 1.43, 95% CI, 0.10-2.76). Poor physical fitness individually increased the risk for new onset obesity, and baseline WSP and poor sleep quality jointly (RERI = 1.87, 95% CI, 0.49-3.24). The presence of more risk factors was dose-dependently associated with onset WSP and to a lesser extent with onset obesity.
  
  
  
  The onset of WSP and the onset of obesity were results of joint effects of exposures. Poor physical fitness was a key covariate in increasing the risk for both conditions. WHAT DOES THIS STUDY ADD?: In a general population, the new onset of widespread pain and new onset of obesity were results of joint effects of risk factors and particularly poor physical fitness. The study may aid in the identification of patients at risk of future disability.
authors.affiliation: National Advisory Unit on Rehabiliation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Magnusson
authors.affiliation: National Advisory Unit on Rehabiliation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.|Department of Health Sciences, Institute of Health and Society, University of Oslo, Norway.
authors.forename: K B
authors.initials: KB
authors.lastname: Hagen
authors.affiliation: Department of General Practice, Institute of Health and Society, University of Oslo, Norway.
authors.forename: B
authors.initials: B
authors.lastname: Natvig
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D059352:Musculoskeletal Pain / Q000150:complications / Q000453:epidemiology*; D009664:Norway / Q000453:epidemiology; D009765:Obesity / Q000150:complications / Q000453:epidemiology*; D010147:Pain Measurement; D010809:Physical Fitness; D011446:Prospective Studies; D012307:Risk Factors; D057566:Self Report; D011795:Surveys and Questionnaires