The 21st century hazards of smoking and benefits of stopping: a prospective study of one million women in the UK

Abstract

Background: Women born around 1940 in countries such as the UK and USA were the first generation in which many smoked substantial numbers of cigarettes throughout adult life. Hence, only in the 21st century can we observe directly the full effects of prolonged smoking, and of prolonged cessation, on mortality among women in the UK.

Methods: For this prospective study, 1·3 million UK women were recruited in 1996-2001 and resurveyed postally about 3 and 8 years later. All were followed to Jan 1, 2011, through national mortality records (mean 12 woman-years, 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 categorised by the age they had stopped smoking. We used Cox regression models to obtain adjusted relative risks that compared categories of smokers or ex-smokers with otherwise similar never-smokers.

Findings: After excluding 0·1 million women with previous disease, 1·2 million women remained, with median birth year 1943 (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 of 2·76 (95% 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 (rate ratio 2·97, 2·88-3·07). Even for women smoking fewer than ten cigarettes per day at baseline, 12-year mortality was doubled (rate ratio 1·98, 1·91-2·04). Of the 30 most common causes of death, 23 were increased significantly in smokers; for lung cancer, the rate ratio was 21·4 (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 (1·14-1·26) for all-cause mortality and 1·84 (1·45-2·34) and 3·34 (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.

Interpretation: Among UK women, two-thirds of all deaths of smokers in their 50s, 60s, and 70s are caused by smoking; smokers lose at least 10 years of lifespan. Although the hazards of smoking until age 40 years and then stopping are substantial, the hazards of continuing are ten times greater. Stopping before age 40 years (and preferably well before age 40 years) avoids more than 90% of the excess mortality caused by continuing smoking; stopping before age 30 years avoids more than 97% of it.

Funding: Cancer Research UK, Medical Research Council.

Copyright © 2013 Elsevier Ltd. All rights reserved.

Figures

Figure 1

All-cause mortality, current versus never-smoker (A) 12-year relative risk by amount smoked (at recruitment). (B) 9-year relative risk by the age at which women first began smoking regularly (as reported at the 3-year postal resurvey). For each category, the area of the square is inversely proportional to the variance of the category-specific log risk (which also determines the CI).

Figure 2

30 most common specific causes of death (ICD-10): 12-year relative risk, current versus never-smoker RR=relative risk. ICD=International Classification of Diseases. *Suicide (ICD-10 X60–64,Y10–34): RR 1·40 (1·12–1·75); transport accident (V01–99): 0·85 (0·60–1·21); and other external: 2·51 (2·11–2·99). The area of each square is inversely proportional to the variance of the log relative risk (vs never-smokers), which also determines the CI.

Figure 3

12-year relative risk, current smoker versus never-smoker, by amount smoked (A) Chronic lung disease. (B) Cancer of the lung. (C) Coronary heart disease. (D) Cerebrovascular disease. For each category, the area of the square is inversely proportional to the variance of the category-specific log risk (which also determines the CI).

Figure 4

9-year relative risk of (A) all-cause mortality and (B) cancer of the lung for ex-smokers by age at stopping (as reported at the 3-year postal resurvey) versus never-smokers The area of each square is inversely proportional to the variance of the log relative risk (vs never-smokers), which also determines the CI.

Figure 5

All-cause mortality: Illustration of the effects of a 3-fold difference in annual death rates on mortality from age 35 years to age 80 years This hypothetical example takes age-specific death rates in non-smokers to be two-thirds of the UK 2010 female rates and those in smokers to be three times as great. NB In a population where at each age 75% have two-thirds of the UK rates and 25% have rates three times as great, the overall death rates in that population would match the UK rates. The horizontal arrows show that the non-smoker rates of death at ages 70 or 80 years are experienced 11 years earlier by smokers, suggesting an 11-year loss of lifespan.