The relationship of smoking cessation to coronary heart disease and lung cancer in the Multiple Risk Factor Intervention Trial (MRFIT).
Level 3 - non-randomized controlled study
Prospective cohort analysis of quitters versus non-quitters within a clinical trial cohort.
PubMed 2368857 · doi:10.2105/ajph.80.8.954
What was done
Researchers evaluated the relationship between smoking cessation and mortality from coronary heart disease (CHD) and lung cancer among 12,866 men enrolled in the Multiple Risk Factor Intervention Trial (MRFIT) after 10.5 years of follow-up. Risk estimates were adjusted for baseline characteristics and changes in other cardiovascular risk factors using Cox proportional hazards models.
What was found
All 119 lung cancer deaths occurred in baseline smokers or ex-smokers, with zero deaths among 1,859 never-smokers. Lung cancer risk showed a dose-response increase with cigarettes smoked per day (B = 0.0203, SE = 0.0076). CHD death was significantly higher in smokers versus nonsmokers (RR = 1.57). Smoking cessation for one year reduced CHD mortality compared to non-quitters (adjusted RR = 0.63), and quitting for at least three years lowered the risk further (RR = 0.38). In contrast, the relative risk of lung cancer mortality among quitters versus non-quitters remained near 1.0 at both 12 months and three years of cessation.
Why it matters
This study shows that cardiovascular mortality benefits from smoking cessation occur rapidly within 1 to 3 years, whereas reductions in lung cancer risk require much longer follow-up periods.
Limits
The study included only middle-aged men at high risk for CHD, limiting generalizability to women and younger populations. Smoking cessation status was observational and self-selected rather than randomized. The 10.5-year follow-up period was insufficient to observe long-term reductions in lung cancer risk.
Cited by
- supports Quitting cigarette smoking reduces the risk of heart disease within one year and halves the risk of lung cancer within ten years.