Job strain in relation to body mass index: pooled analysis of 160,000 adults from 13 cohort studies

Background: Evidence of an association between job strain and obesity is inconsistent, mostly limited to small-scale studies, and does not distinguish between categories of underweight or obesity subclasses. Objectives: To examine the association between job strain and body mass index (BMI) in a large adult population. Methods We performed a pooled cross-sectional analysis based on individual-level data from 13 European studies resulting in a total of 161 746 participants (49% men, mean age, 43.7 years). Longitudinal analysis with a median follow-up of 4 years was possible for four cohort studies (n = 42 222). Results: A total of 86 429 participants were of normal weight (BMI 18.5–24.9 kg m−2), 2149 were underweight (BMI < 18.5 kg m−2), 56 572 overweight (BMI 25.0–29.9 kg m−2) and 13 523 class I (BMI 30–34.9 kg m−2) and 3073 classes II/III (BMI ≥ 35 kg m−2) obese. In addition, 27 010 (17%) participants reported job strain. In cross-sectional analyses, we found increased odds of job strain amongst underweight [odds ratio 1.12, 95% confidence interval (CI) 1.00–1.25], obese class I (odds ratio 1.07, 95% CI 1.02–1.12) and obese classes II/III participants (odds ratio 1.14, 95% CI 1.01–1.28) as compared with participants of normal weight. In longitudinal analysis, both weight gain and weight loss were related to the onset of job strain during follow-up. Conclusions: In an analysis of European data, we found both weight gain and weight loss to be associated with the onset of job strain, consistent with a ‘U’-shaped cross-sectional association between job strain and BMI. These associations were relatively modest; therefore, it is unlikely that intervention to reduce job strain would be effective in combating obesity at a population level.