Association of the age at smoking initiation and cessation on all-cause and cause-specific mortality: The Japan Collaborative Cohort Study

We estimated the association between the age at smoking initiation and cessation and all-cause and cause-specific mortality among Japanese men (n = 41,711; age 40-79 years) by analyzing data from the Japan Collaborative Cohort Study for the Evaluation of Cancer Risks. From 1988 and 1990 to 2009, 13,429 all-cause deaths (cancers, n = 4999; cardiovascular diseases, n = 3682) occurred in this cohort. Fitted Cox proportional hazard models, with never smokers as the reference group, were created. Former smokers demonstrated a lower risk for all-cause and cause-specific mortality than current smokers, with a dose-dependent reduction in the risk based on smoking-initiation age. Among former smokers who quit smoking aged 50 years or more, the highest hazard ratios were detected for those who started smoking at <20 years of age (all-cause, cancer, and cardiovascular disease mortality, hazard ratio [95% confidence interval] 1.51 [1.29-1.77], 1.68 [1.27-2.23], and 1.48 [1.12-1.96], respectively). Former smokers who quit smoking at <50 years of age had negligible all-cause or cardiovascular disease mortality regardless of the smoking-initiation age, whereas the cancer mortality risk remained significantly high among those who quit smoking at 40-49 years of age. Thus, smoking cessation significantly reduces the all-cause mortality risk; however, early initiation and later cessation do not provide a huge benefit, which earlier cessation does. Therefore, all smokers should be encouraged to quit smoking earlier in life regardless of their age at smoking initiation.