Does Obesity Modify the Relationship between Exposure to Occupational Factors and Musculoskeletal Pain in Men? Results from the GAZEL Cohort Study

et al. (2014) Does Obesity Modify the Relationship between Exposure to Occupational Factors and Musculoskeletal Pain in Men? Results from the GAZEL Cohort Study. PLoS ONE 9(10): e109633. doi:10.1371/journal.pone.0109633 Does Obesity Modify the Relationship between Exposure to Occupational Factors and Musculoskeletal Pain in Men? Results from the GAZEL Cohort Study Anastasia Evanoff 0 Erika L. Sabbath 0 Matthieu Carton 0 Sebastien Czernichow 0 Marie Zins 0 Annette Leclerc 0 Alexis Descatha 0 C. M. Schooling, CUNY, United States of America 0 1 Univ Versailles St-Quentin, Versailles, France, 2 UMS 011 Population-based Epidemiologic Cohorts Unit Inserm, Villejuif, France, 3 Harvard College , Cambridge, MA , United States of America, 4 Harvard Center for Population and Development Studies , Cambridge, MA , United States of America, 5 Department of Nutrition, Assistance Publique-Hopitaux de Paris, Ambroise Pare University Hospital , Boulogne-Billancourt , France , 6 Occupational Health Unit/EMS (Samu92), AP-HP, University hospital of Poincare , Garches , France Objective: To analyze relationships between physical occupational exposures, post-retirement shoulder/knee pain, and obesity. Methods: 9 415 male participants (aged 63-73 in 2012) from the French GAZEL cohort answered self-administered questionnaires in 2006 and 2012. Occupational exposures retrospectively assessed in 2006 included arm elevation and squatting (never, ,10 years, $10 years). ''Severe'' shoulder and knee pain were defined as $5 on an 8-point scale. BMI was self-reported. Conclusion: Obesity plays a role in relationships between occupational exposures and musculoskeletal pain. Further prospective studies should use BMI in analyses of musculoskeletal pain and occupational factors, and continue to clarify this relationship. - Introduction Musculoskeletal disorders (MSDs) include a wide range of diseases and injuries that comprise the largest category of workrelated illnesses. MSDs are a main cause of disability, especially in aging populations. [1] Many studies have shown that occupational factors such as repeated exposure to arm elevation or squatting in the workplace predict subsequent MSDs in the shoulders and knees. [24] Previous analyses have been performed on these joints with a particular focus on associations between long-term biomechanical exposure and incidence of severe pain; consistent associations have been found between repeated exposure to arm elevation or squatting in the workplace and severe shoulder and knee pain. [5,6] Self-reported symptoms of pain are the most common criterion used to assess the presence of MSDs. [1] Recommendations emphasize the use of instruments such as Nordic-style questionnaires, [7] especially with numeric scales of disability intensity and pain [8]. Obesity has become a worldwide epidemic, affecting over onethird of the adult population in the United States and about 15% in France. [9] Obesity may also be a risk factor for shoulder and knee pain [1013]; thus, rising obesity rates could partly explain the increasing levels of observed musculoskeletal pain and disability [14]. In addition to being a risk factor for MSDs, recent studies have found that obesity may also be a consequence of occupational exposures, potentially mediating and/or modifying effects of occupational factors on musculoskeletal pain. [1517] Furthermore, occupational exposures may be risk factors for obesity. [15,16] Some suggest that obesity may increase mechanical forces on the joints and change the metabolic demands of the body, both of which would lead to higher rates of MSDs. [13,18] Thus, the nature of the interrelationships between occupational exposures, obesity, and musculoskeletal pain are complex; more research is needed to understand the nature of such relationships. This study aims to disentangle associations between occupational exposures, obesity, and pain in shoulders and knees. We hypothesized that occupational exposures may be significant contributors to incidence of musculoskeletal pain among overweight and obese patients, and that the relationships may differ for upper and lower limbs. Sample All participants in this study were members of the GAZEL cohort (n = 20 625; 15 010 are men), all employed by the French national power utility (EDF-GDF). [19] Each January, participants receive general questionnaires about lifestyle, health, and occupational status; in 2006 and 2012, questions about pain were included. Few subjects are lost to follow-up, although not all subjects answer the questionnaire every year. The present analysis included men who answered both 2006 and 2012 questionnaires (n = 9 450). For each analysis, we excluded those reporting severe pain in 2006 (n = 1 443 for shoulder, n = 1 408 for knee), to determine the number of new cases (incident cases) that developed by 2012. We also excluded underweight participants (n = 35) and those missing 2006 data on smoking (n = 416), and BMI (n = 246). Thus, our final analytic n = 7310 for shoulder pain and n = 7345 for knee pain. We excluded women because of low prevalence of biomechanical exposures (4.82% exposed to elevated arms, 3.15% to squatting). Variables The main outcome variables in this study are severe shoulder and severe knee pain in 2012. Pain was reported on a scale of 1 (lowest pain) to 8 (highest pain). We dichotomized the scale at the midpoint (severe pain $5, little to no pain #4) based on French convention. [5,6,8] Our main exposure variable was lifetime exposure to each of eight physical occupational tasks, retrospectively self-reported in 2006. Participants were asked for how long (never, ,10 years, $10 years) they were exposed to working with one or two arms in the air (above the shoulders) regularly or in a prolonged manner (for shoulder pain analyses) or working in a squatting position (for knee pain analyses). BMI (kg/m2) in 2006, using self-reported height and weight, was categorized as normal ($18.5,25 kg/m2, overweight ($25,30 kg/m2), or obese ($ 30 kg/m2). We also included age and current smoking in 2006 (yes/no). Analysis We determined the number of incident cases in 2012 by excluding those with severe pain in 2006, and counting only new cases. We modeled associations between occupational factors, BMI, and new shoulder or knee pain in 2012 using logistic regression, estimating odds ratios (OR) and confidence intervals (95% CI). We present results stratified by BMI categories to illustrate the modifying effect of BMI on relationships between occupational factors and pain. Multiplicative interactions were also tested between BMI and occupational factors. All models were adjusted for age and smoking. Stata/MP, version 12.1, was used for all statistical analyses (StataCorp LP, College Station, TX, USA). Associations were considered statistically significant if twotailed P-values were ,0.05. Authorization from the appropriate ethics committee was obtained ( Comite Consultatif Natio (...truncated)