(HealthDay News) – For U.K. women, the hazards of smoking and benefits of quitting are considerable, with women who quit before age 30 avoiding more than 97% of excess smoking-related mortality.

In an effort to examine the full effects of prolonged smoking, and prolonged cessation, on mortality, Kirstin Pirie, from the University of Oxford in the United Kingdom, and colleagues conducted a prospective study involving 1.2 million U.K. women, recruited in 1996–2001, and resurveyed three and eight years later.

The researchers found that, for 12-year mortality, the mortality rate ratio for those smoking at baseline was 2.76, compared with never-smokers. Those still smoking at the three-year resurvey had a three-fold increased risk of mortality, largely irrespective of age (rate ratio, 2.97). Twenty-three of the 30 most common causes of death were significantly elevated in smokers, with a rate ratio of 21.4 for lung cancer. Compared with never-smokers, the excess mortality for smokers was mainly from smoking-related disease, such as lung cancer. For ex-smokers who stopped at age 25–34, the relative risks for all-cause and lung-cancer mortality were 1.05 (95% confidence interval, 1.00–1.11) and 1.84, respectively, and for those who stopped at age 35–44, the risks were 1.20 and 3.34, respectively. Data suggest that 53% of smokers and 22% of never-smokers die before age 80 years, with an 11-year difference in life span.

“Although the hazards of smoking until age 40 years and then stopping are substantial, the hazards of continuing are 10 times greater,” the authors write. “Stopping before age 40 years (and preferably well before age 40 years) avoids >90% of the excess mortality caused by continuing smoking; stopping before age 30 years avoids >97% of it.”

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