The 21st Century Hazards of Smoking and Benefits of Stopping: A Prospective Study of One Million Women in the UK
What are the hazards of smoking and the benefits of having stopped at various ages, based on 21st century mortality rates?
For this prospective study, 1.3 million UK women were recruited in 1996-2001 and resurveyed postally approximately 3 and 8 years later. All were followed to January 1, 2011, through national mortality records (mean 12 woman-years, standard deviation [SD] 2). Participants were asked at entry whether they were current or ex-smokers, and how many cigarettes they currently smoked. Those who were ex-smokers at both entry and the 3-year resurvey and had stopped before the age of 55 years were categorized by the age they had stopped smoking. The authors used Cox regression models to obtain adjusted relative risks that compared categories of smokers or ex-smokers with otherwise similar never-smokers.
After excluding 0.1 million women with previous disease, 1.2 million women remained, with median birth year 1943 (interquartile range [IQR], 1938-46) and age 55 years (IQR, 52-60). Overall, 6% (66,489/1,180,652) died, at mean age 65 years (SD, 6). At baseline, 20% (232,461) were current smokers, 28% (328,417) were ex-smokers, and 52% (619,774) were never-smokers. For 12-year mortality, those smoking at baseline had a mortality rate ratio (RR) of 2.76 (95% confidence interval [CI], 2.71-2.81) compared with never-smokers, even though 44% (37,240/85,256) of the baseline smokers who responded to the 8-year resurvey had by then stopped smoking. Mortality was tripled, largely irrespective of age, in those still smoking at the 3-year resurvey (RR, 2.97; 95% CI, 2.88-3.07). Even for women smoking fewer than 10 cigarettes per day at baseline, 12-year mortality was doubled (RR, 1.98; 95% CI, 1.91-2.04). Of the 30 most common causes of death, 23 were increased significantly in smokers; for lung cancer, the RR was 21.4 (95% CI, 19.7-23.2). The excess mortality among smokers (in comparison with never-smokers) was mainly from diseases that, like lung cancer, can be caused by smoking. Among ex-smokers who had stopped permanently at ages 25-34 years or at ages 35-44 years, the respective relative risks were 1.05 (95% CI, 1.00-1.11) and 1.20 (95% CI, 1.14-1.26) for all-cause mortality and 1.84 (95% CI, 1.45-2.34) and 3.34 (95% CI, 2.76-4.03) for lung cancer mortality. Thus, although some excess mortality remains among these long-term ex-smokers, it is only 3% and 10% of the excess mortality among continuing smokers. If combined with 2010 UK national death rates, tripled mortality rates among smokers indicate 53% of smokers and 22% of never-smokers dying before age 80 years, and an 11-year lifespan difference.
The authors concluded that among UK women, two-thirds of all deaths of smokers in their 50s, 60s, and 70s are caused by smoking, and smokers lose at least 10 years of lifespan.
This study suggests that women who have smoked cigarettes throughout adult life have as a result three times the overall mortality rate of otherwise similar women who have never smoked, or who stopped well before middle age. Furthermore, stopping before 40 years of age avoids more than 90% of this excess mortality, and stopping before 30 years of age avoids more than 97% of it. However, the residual hazards among those who smoke until age 40 years and then stop are substantial, as decades later, they still have 1.2 times the mortality rate of never-smokers. Overall, it appears that if women stop smoking early enough, they may gain 10 extra years of life expectancy.
Keywords: Cause of Death, Middle Aged, Life Expectancy, Cardiovascular Diseases, Risk Factors, Confidence Intervals, Tobacco Use Disorder, Smoking Cessation, Lung Neoplasms, Smoking
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