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Although much is known about the effects of smoking, there is limited reliable information on the effects of stopping smoking on mortality.
To investigate the association between stopping smoking and the risk of all-cause mortality and of cause specific mortality, including deaths due to cancer and vascular disease. In particular, to investigate how the risks for former smokers compare with those of lifelong non-smokers as the period of time since quitting smoking increases.
Prospective cohort study.
Participants and Setting
1.3 million UK women were recruited in 1996–2001, and were resurveyed around 3 years later with a 65% response rate. Women were included in these analyses (n = 700 000) if they had completed both study questionnaires, and if smoking status was classified in the same way (current, former, never smoker) on both. Participants were followed prospectively for incident cancers and death through NHS cancer registration and death records.
Main Outcome Measures
Relative risks of all-cause and cause-specific mortality for former smokers compared with lifelong non-smokers, adjusting for age, region, socioeconomic status and body mass index.
Women were followed up for a mean duration of 6.7 years, during which time 21 469 deaths occurred, including 12 588 deaths due to cancer and 4314 due to vascular disease. Current smokers were almost three times more likely to die from any cause than lifelong non-smokers (RR 2.8, 95% CI 2.7 to 2.9). The risk for former smokers declined with every decade that passed since stopping smoking, with women who had stopped 30 or more years ago at no greater risk of mortality than lifelong non-smokers (RR 1.0, 95% CI 0.9 to 1.1). Results will be presented according to time since stopping smoking, and by cause of mortality.
The Million Women Study is the largest study to date to examine the direct health effects of smoking, and the benefits of stopping, in women who have smoked throughout much of their adult lives. Much of the excess mortality risk associated with smoking is removed by stopping smoking, with former smokers who had not smoked for 30 years or more at no greater risk than women who had never smoked.
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