HealthDay News — Participants in Great Britain’s Million Women Study who quit smoking experienced dramatically improved life-expectancy compared with those who continued to smoke, researchers found.
The hazards of smoking and benefits of quitting are considerable, with women who quit before age 30 years avoiding more than 97% of excess smoking-related mortality, Kirstin Pirie, MSc, of the University of Oxford in England, and colleagues reported in Lancet.
“Even cessation at about 50 years of age avoids at least two-thirds of the continuing smoker’s excess mortality in later middle age,” the researchers wrote.
Although those who quit smoking around age 50 years remained at significantly higher risk for all-cause mortality compared with never-smokers (relative risk=1.56; 95% CI: 1.49-1.64), mortality risk in this population was still much lower than the tripled risk observed in current smokers.
Much of the research linking smoking to early mortality was performed at a time when most long-time smokers were men, before smoking peaked in women in the 1960s, so smoking-related mortality among women appeared to be lower in the avavilable data.
In an effort to examine the full effects of prolonged smoking, and prolonged cessation on mortality in this population, Pirie and colleagues conducted a prospective study involving 1.2 million UK women, recruited from 1996 to 2001. Participants completed surveys on current and past smoking at recruitment, and again three and eight years later.
The study population was comprised of 620,000 never-smokers at recruitment, 329,000 who had quit at some point in the past, and 232,000 who reported current smoking.
At the second survey, 23% of of current smokers at enrollment said they had quit. At eight-year follow-up, this proportion rose to 44%.
The researchers collected data on mortality using Great Britain’s comprehensive registry, including the cause listed on death certificates. Approximately 66,000 participants (6%) died during follow-up.
The 12-year mortality rate ratio for those smoking at baseline was 2.76 (95% CI: 2.88 -3.07) compared with those who did not smoke — roughly triple the rate observed in never-smokers, the researchers found.
Mortality risk was substantially greater even among light smokers (those who smoked fewer than 10 cigarettes per day) — with a 12-year mortality rate ratio of 1.98 (95% CI:1.91-2.04) compared with never-smokers.
Excess mortality for smokers was mainly from smoking-related disease, such as lung cancer. Of the 30 most common causes of death in the UK, 23 were significantly greater in current smokers. Notably, the rate ratio for chronic lung diseases was 35.3 (95% CI: 29.2-42.5), and for lung cancer it was 21.4 (95% CI 19.7 to 23.2).
The benefits of quitting smoking were greatest for those who quit smoking earlier. For participants who stopped smoking by their mid-30s, the risk of all-cause mortality was hardly different from that of never-smokers (RR 1.05; 95% CI: 1.00 -1.11). Those quitting at ages 35 to 44 years were at 20% greater risk for death than never-smokers, and those quitting at 45 to 54 years were at 56% increased risk.
Overall data suggest that 53% of smokers and 22% of never-smokers die before age 80 years, with an 11-year difference in life span.
However, lung cancer risk was significantly increased in ex-smokers regardless of the age at quitting — with relative risks of 1.56 in those stopping before age 25 to 5.91 in participants quitting at 45 to 54, all with minuscule P values. These rates were still much lower than the greater than 20 relative risk observed in those still smoking.
In an accompanying editorial, Rachel R. Huxley, PhD, of the University of Minnesota in Minneapolis, and Mark Woodward, MD, of the University of Sydney in Australia, praised the study for it’s comprehensiveness.
“Aside from its impressive sample size, the Million Women Study is distinct from previous large cohorts — and superior for assessment among women of the full eventual hazards of prolonged smoking and the full benefits of long-term cessation — because the participants were among the first generation of women in the U.K. in which smoking was widespread in early adult life, and although many continued smoking, many stopped before age 30 or 40 years,” they wrote.
Huxley and Woodward called for “effective sex-specific and culturally specific tobacco control policies” to encourage those who already smoke to quit and discourage children and adolescents from picking up the habit.