The indirect effects of socioeconomic position on lung function: a mediation analysis

BACKGROUND: There is a strong link between socioeconomic position and pulmonary health, but less is known about their connecting pathways. We analyzed the direct and indirect effects of education and deprivation on lung function using air pollutants in a mediation framework. METHODS: We used spirometry tests, demographic, and health information on 5703 Czechs, with a mean age of 58.3 ± 7.1 years from the Health, Alcohol, and Psychosocial Factors in Eastern Europe (HAPIEE) cohort study between 2002 to 2005. The annual means of particulate matter 10 (PM10), particulate matter 2.5 (PM2.5), and nitrogen dioxide (NO2) estimated by Shen et al. (2022) for the years 2000 to 2003 were matched to the geographic addresses of the participants. Multiple mediation analyses assessed the relationship between socioeconomic variables (education and deprivation) and the predicted percentage of Forced Expiratory Volume in the first second (FEV1) and the role of mediators: PM10 or PM2.5 or NO2, smoking behavior, and body mass index (BMI). The models were adjusted for sex, age. RESULTS: 9.27% of individuals had <70% of the predicted percentage of FEV1. We tested the first model using PM10, smoking, and BMI as mediators. We found significant indirect effects from education through PM10 (β = 0.17, CI95%: 0.10-0.25), BMI (β = 0.36, 0.25-0.47), and smoking (β = 0.17, 0.08-0.25) with indirect effects explaining 34% of the total effect of education. The indirect effect of deprivation was significant only through smoking (β=-0.11, -0.14 to -0.07), explaining 31% of the effect of deprivation. Similar results were observed when we tested a second model using PM2.5 instead of PM10, and a third model including NO2 instead of PM10. CONCLUSIONS: Air pollutants seem to mediate the association between education and lung function, but not between deprivation and lung function, however, further research is needed to confirm our findings. KEY MESSAGES: • Higher education appears to be associated with better environmental factors that prevent loss of lung function. • Most of the routes that connect socioeconomic factors and lung function remain unclear.