Social factors and chronic pain : The modifying effect of sex in the Stockholm Public Health Cohort Study

OBJECTIVES: To assess the relation between social factors (socioeconomic status, household load and job strain) and chronic pain occurrence, and the role of gender in this relation. METHODS: We used data corresponding to 8 years of follow-up of the Stockholm Public Health Cohort Study (2006 to 2014) to compute Adjusted Incidence Rate Ratios (IRR) and additive interaction measures of chronic pain episodes, social factors, and sex in 16,687 subjects. RESULTS: For men, increased rates were observed for skilled workers (IRR=1.27, 95% Confidence Interval (CI): 0.99, 1.61) and lower non-manual employees (IRR=1.37, 95%CI: 1.05, 1.78), compared to unskilled workers; subjects with high household load (IRR=1.39; 95%CI: 1.03, 1.88), compared to those with null score; and active jobs (IRR=1.27, 95%CI: 1.06, 1.51), compared to low strain jobs. For women, we observed decreased rates for lower (IRR=0.82, 95%CI: 0.68, 0.99), intermediate (IRR=0.74, 95%CI: 0.63, 0.88) and higher non-manual employees (IRR=0.65, 95%CI: 0.54, 0.79), compared to unskilled workers. Compared to subjects with a null score, women with low household load showed a lower rate (IRR=0.85; 95%CI: 0.72, 1.00). Compared to low strain jobs, passive jobs (IRR=1.21; 95%CI: 1.02, 1.44) and high strain jobs (IRR=1.46; 95%CI: 1.02, 2.09) showed higher rates. CONCLUSION: In general, our analysis yielded different results, if not opposite, when data were stratified by sex. Sex may then represent an effect modifier of the relation between social factors and chronic pain. RHEUMATOLOGY KEY MESSAGES: Low socioeconomic status and high job strain household load are related to chronic pain occurrence.Sex is an effect modifier of the relation between socioeconomic status and chronic pain; that is, this relation is different between men and women