Temporal associations between smoking prevalence and smoking-related mortality: a US state-level ecological study.

Introduction: Smoking is the leading cause of preventable deaths worldwide. Consequently, smoking reduction interventions have major long-term public health benefits. However, the temporal association of smoking-related mortality remains ill-defined. Therefore, this study describes the lag-response of smoking prevalence reduction on smoking-related mortality. Methods: Our study included smoking prevalence and mortality for the US states. Generalised additive models (GAM) with random intercepts were used to model the cause-specific mortality as a function of the smoking prevalence history. The lag-response of an absolute 5% smoking prevalence reduction was estimated using a distributed lag non-linear model. Covariables were included accounting for demographics, socioeconomic status and general trends. Results: Based on smoking prevalence data from 8 354 095 people, the relationship between smoking prevalence history and smoking-related mortality rates appeared non-linear. The largest association with mortality (per 100 000 person-years) caused by ischaemic heart disease was observed at 8 years (-3.02 (95% CI -4.31 to -1.73)), 10 years for chronic obstructive pulmonary disease (COPD) (-1.35 (95% CI -1.89 to -0.82)), 11 years for lung cancer (-1.68 (95% CI -2.44 to -0.91)) and for other smoking-related cancers at 20 years (-0.61 (95% CI -0.81 to -0.40)).Notably, COPD mortality showed a rapid decline. Our results estimated an absolute 5% reduction in smoking prevalence from 1999 onwards is associated with a reduced mortality in 2019 by 23.91% (95% CI 15.36% to 32.46%) for ischaemic heart diseases, 30.82% (95% CI 22.81% to 38.83%) for COPD, 25.20% (95% CI 18.85% to 31.55%) for lung cancer and 7.88% (95% CI 5.24% to 10.52%) for other smoking-related cancers. Conclusion: Impact and timing of smoking reduction vary across causes of death. Notably, COPD-related deaths decrease rapidly. The largest association of smoking prevalence on COPD and lung cancer mortality occurred after 10 years and 11 years, while for ischaemic heart diseases, it was at 8 years.