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

Women born around 1940 in countries such as the UK and US 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.

For this prospective study, 1.3 million UK women were recruited in 1996-2001 and resurveyed postally about three and eight years later.¹ All were followed to January 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 three-year resurvey and had stopped before the age of 55 years were categorised by the age they had stopped smoking. Cox regression models were used 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 (IQR 1938-1946) 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
• 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 eight-year resurvey had by then stopped smoking. 

Mortality was tripled, largely irrespective of age, in those still smoking at the three-year resurvey (rate ratio 2.97, 2.88-3.07). Even for women smoking fewer than 10 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.

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 10 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.

Reference

1. Pyrie K, Peto R, Reeves GK et al, Lancet 2012; doi: 10.1016/S0140-6736(12): 61720-61726