The scientists say that other new research suggests similar effects in men.
British researchers recruited 1.3 million women were to a study between 1996 and 2001, at ages 50 to 65 years. Participants filled out a questionnaire about lifestyle, medical and social factors and were resurveyed by mail three years later. Women were traced for an average of 12 years from when they joined. The findings were published in the medical journal The Lancet on Oct. 27.
Initially, 20 percent of the study participants were smokers, 28 percent were ex-smokers, and 52 percent had never smoked. Those who were still smokers three years later were found to be nearly three times as likely as non-smokers to die over the next nine years, even though some reduced their risk by stopping smoking during this period.
The threefold death rate ratio means that two-thirds of all deaths of smokers in their 50s, 60s, and 70s are caused by smoking, as most of the difference between smokers and non-smokers came from smoking-related diseases such as lung cancer, chronic lung disease, heart disease, or stroke, the researchers said.
The risks among smokers increased steeply with amount smoked, although even for those who smoked just one cigarette a day at the start of the study, mortality rates were double those for non-smokers.
Both the hazards of smoking and, accordingingly, the benefits of stopping are bigger than previous studies have suggested, the investigators said. Smokers who stopped around age 30 were found to avoid 97 percent of their excess risk of premature death, and although serious excess hazards remained for decades among those who smoked until age 40 before stopping, the excess hazards among those who continued smoking after age 40 were ten times bigger.
“If women smoke like men, they die like men – but, whether they are men or women, smokers who stop before reaching middle age will on average gain about an extra ten years of life,” said study co-author Richard Peto, at the University of Oxford, UK. “Both in the UK and in the USA, women born around 1940 were the first generation in which many smoked substantial numbers of cigarettes throughout adult life. Hence, only in the 21st century could we observe directly the full effects of prolonged smoking, and of prolonged cessation, on premature mortality among women.”
The authors wrote that they found “the proportional excess risk in smokers was more marked than in many previous studies, but recently updated analyses of 21st century mortality in six smaller cohorts of U.S. smokers now suggest, in aggregate, similar hazards from smoking and benefits of stopping, as does a recent study in Japanese men and women.”
As for their own study, Peto and colleagues wrote further that “although the relative risks for the effects of prolonged smoking on particular diseases cannot be generalised exactly to populations with very different background rates of those diseases, they should be approximately generalisable to many (though not all) countries where women smoke.”
The research was published to mark the 100th anniversary of the birth of Sir Richard Doll, one of the first people to identify the link between lung cancer and smoking.
No comments:
Post a Comment