Regional effects unlikely to explain association between ozone and cardiovascular mortality in China

概要

We read with interest the Article by Yue Niu and colleagues in The Lancet Planetary Health in which they found an association between long-term ozone exposure and increased risks of cardiovascular mortality in China.1 The study could provide additional evidence of this association in middle-income countries; however, we have concerns regarding their subgroup analysis.

The association between exposure to ozone and the outcomes was analysed by age and sex stratified Cox proportional hazards models adjusted for several confounders. Furthermore, the authors did several subgroup analyses. The authors intended to analyse between- group differences in the subgroup analyses, but did not discuss the changes in parameter estimates from the original analysis. Although the subgroup analyses for age, sex, education, and smoking showed different hazard ratios (HRs) in each stratum, each analysis gave a point estimate of approximately 1·093, which was similar to the original point estimate in the non-stratified analysis.