Socioeconomic inequality in exposure to second-hand smoke among middle-aged adults of the RaNCD cohort study: a decomposition analysis

Abstract Background Secondhand smoke (SHS) can cause various health problems among different age groups worldwide. Socioeconomic factors may influence the distribution of SHS exposure among population subgroups. We aimed to estimate socioeconomic inequality in SHS exposure and identify its contributing factors among a sample of Iranian adults. Methods This cross-sectional investigation utilized baseline data from the Ravansar Non-Communicable Disease cohort study. The study population comprised 7991 middle-aged adults aged between 35 and 65 years. To determine socioeconomic status (SES) principal component analysis (PCA) was used. The Wagstaff normalized concentration index (Cn) was utilized to measure the extent of socioeconomic inequality in SHS. Furthermore, decomposition analysis was performed to identify the factors contributing to the observed inequality in SHS exposure. Results The prevalence of SHS exposure among men, women, and the total population was 38.23%, 47.29%, and 43.89%, respectively. The concentration index (Cn) value for SHS exposure was − 0.121 (95% confidence interval [CI]: -0.146, -0.096) in the study participants. Among men and women, the values were − 0.080 (95% CI: -0.122, -0.037) and − 0.095 (95% CI: -0.112, -0.063), respectively, indicating a higher concentration of SHS among individuals with low SES. Female sex (35.17%), socioeconomic status (31.83%), being married (-26.36%), and rural residency (22.44%) were identified as the primary factors contributing to the observed inequality in SHS exposure. Conclusion The research findings revealed a pro-rich inequality in SHS, with a significant concentration among low-SES individuals. In terms of the main contributors to socioeconomic inequality in SHS exposure, policy interventions need to pay attention to females, individuals with low SES, and married individuals to address inequality in SHS exposure.