BACKGROUND: Smoking cessation reduces mortality and morbidity. However, the extent and rapidity at which cessation reduces contemporary death rates from smoking-related illnesses remains uncertain.
METHODS: We pooled current or former vs. never cigarette smoker hazard ratios (HRs) from four national cohorts with linkage to death registries in the United States, United Kingdom, Norway, and Canada among adults aged 20-79, conducted from 1974-2018. We calculated excess risk differences and survival comparing current or never smokers with age-specific cessation and cessation <3, 3-9, or ≥10 years earlier.
RESULTS: Among 1.48 million adults followed for 15 years, 122,697 deaths occurred. Adjusting for age, education, alcohol use, and obesity, current smokers had significantly higher HRs for death compared to never smokers (2.8 for women, 2.7 for men). Survival between ages 40-79 years were 12 and 13 years less in women and men, respectively who smoked compared with never smokers (about 24-26 years of life lost for smokers killed by smoking combined with zero loss for smokers who were not). Former smokers showed lower HRs (1.3 in both sexes). Short-term cessation <3 years reduced excess risk by 95% in women and 90% in men below age 40, with notable beneficial associations also in women and men aged 40-49 years (81% and 61%) and 50-59 years (63% and 54%). Cessation at every age raised survival, particularly cessation before age 40 years. Among all ages and compared to continued smoking, cessation of <3 years averted 5 years of life lost and cessation for ≥10 years averted about 10 years of life lost, yielding survival similar to never smokers.
CONCLUSIONS: Quitting smoking at any age, but particularly in younger years, was strongly associated with significantly lower excess mortality overall and from vascular, respiratory, and neoplastic diseases. Benefits were evident as early as 3 years after cessation.