Smoking cessation-associated mortality reduction: A case-control study in Tianjin city, China

Introduction Smoking-attributed mortality is increasing steadily in most developing countries. The aim of the study is to assess the reduction in smoking-associated mortality following cessation. Methods Death data were collected from 2016 to 2017. Cases were deaths from pre-defined diseases of interest (65298); controls were deaths from pre-defined non-smoking-related diseases (13527). Case versus control odds ratios for ex-smokers versus smokers were calculated by age, sex, marital status and education with standardized logistic regression. These are described as mortality rate ratios (RRs, calculated as odds ratios), with a group-specific confidence interval (CI). The statistical analysis of the data was conducted from June to August 2019. Results For deaths from pre-defined non-smoking-related diseases at age 35-59 years, the RRs for quitting smoking 0-4, 5-9 or ≥10 years ago and never smoking were 0.66 (95% CI: 0.55-0.78), 0.58 (95% CI: 0.38-0.88), 0.61 (95% CI: 0.45-0.82), and 0.43 (95% CI: 0.39-0.46), respectively. The same trend was found at ages 60-69 years and 70-79 years. Younger age of quitting (25-44 or 45-64 years) appeared to be associated with greater protection among the age groups: RR was 0.55 (95% CI: 0.42-0.74) and 0.67 (95% CI: 0.56-0.79), respectively, at age 35-59 years. Among the patients who died of lung cancer, the strong protective effect can only be observed when the duration of quitting is ≥10 years. The effect of smoking cessation on the risk of death from cardiovascular disease can be observed when the duration of quitting is 1-5 years. Conclusions Longer durations of smoking cessation are associated with progressively lower mortality rates from the diseases of interest, such as lung cancer and other smoking related cancers. For sustainable monitoring of tobacco-attributed mortality, smoking information over decades, such as smoking duration and quit smoking years, should be recorded during registration of death.