Women who quit smoking by the age of 30 almost completely avoid the risk of an early tobacco-related death — by more than 97 percent — according to a study of more than a million women in the United Kingdom.
Conversely, lifelong smokers on average die 10 years earlier than non-smoking women.
The results were published Saturday in The Lancet, one of the world's oldest, and most respected general medical journals. According to the journal's Web site, the results "commemorate the 100th anniversary of the birth of Sir Richard Doll, one of the first people to identify the link between smoking and lung cancer."
"What we've shown is that if women smoke like men, they die like men," lead researcher Sir Richard Peto told the BBC. "More than half of women who smoke and keep on smoking will get killed by tobacco.
"Stopping works, amazingly well actually. Smoking kills, stopping works and the earlier you stop the better."
On average, women who stopped smoking by 30 lost a month of life and if they stopped by 40 they died a year younger.
The BBC reported that "Professor Peto added the crucial risk factor was "time" spent smoking, rather than amount."
"If you smoke 10 cigarettes a day for 40 years it's a lot more dangerous than smoking 20 cigarettes a day for 20 years," Peto said. "Even if you smoke a few cigarettes a day then you're twice as likely to die at middle age."
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The risk of "social smoking" a few times a week was more difficult to gauge, he noted.
The study followed 1.3 million women in the UK born around 1940, since that was the first generation when women began a prolonged habit of smoking, like men, according to the researchers. As the study says, "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."
The results showed that women who smoked fewer than 10 cigarettes a day were more than twice as likely to die sooner than non-smokers — the same as it is for men, Peto told to the BBC.
The research, which was funded by the Medical Research Council in the UK, was collected from the Million Women Study, conducted between 1996 and 2001 when women between the ages of 50 and 65 "went for breast cancer screening. ... The study, unique because of its size, has compiled a vast amount of information on women's health and led, among other things, to important findings on risk factors for breast cancer," according to an online story in the Guardian.
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When women started smoking is also relevant. Those who "picked up the habit at a young age increased the length of time for which they smoked and their risk of an early death," the Guardian reported.
According to the Center for Disease Control and Prevention, "an estimated 45.3 million people, or 19.3 percent of all adults (aged 18 years or older), in the United States smoke cigarettes. Cigarette smoking is more common among men (21.5 percent) than women (17.3 percent)."
The CDC also reports that "cigarette smoking is the leading cause of preventable death in the United States, accounting for approximately 443,000 deaths, or 1 of every 5 deaths, in the United States each year."