http://bmj.com/cgi/content/full/324/7353/1544/d
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Owen Dyer London
Smoking is even more dangerous than previously believed, according to a major review of epidemiological data by the World Health Organization’s cancer agency. The International Agency for Research on Cancer (IARC) also published the first evidence to link conclusively second hand smoke with increased risk of cancer.
The agency convened 29 scientists from 12 countries to review all significant published research on both active and passive smoking. They state unequivocally that even an average degree of passive exposure to tobacco products can cause lung cancer in people who have never smoked.
"It’s been suspected for a long time," said Professor Richard Doll, one of the report’s authors, "but this is the first time we’ve had a clear scientific consensus saying it’s definitely a cause."
Fifty years ago, Professor Doll was joint author of the first published paper to suggest a link between tobacco and lung cancer.
The agency’s report also implicates tobacco in five cancer sites not previously shown to be associated with smoking—the stomach, liver, uterine cervix, kidney (renal cell carcinoma), and myeloid leukaemia. "The additional risk to these sites from smoking varies from about 30% to double," said Professor Doll. "Some were previously suspected, but this is the first time there is solid evidence."
"I myself was surprised to learn of a link between smoking and cervical cancer," he said. "It’s been hard to prove because smokers tend to be more sexually active than non-smokers. But if you look just at people with HPV [human papillomavirus] infection, you’ll find the smokers are more likely to develop malignancies."
Cancers normally linked to hormonal causes seem to be unaffected by smoking. In particular, the agency's working group rejected suggestions that passive smoking can cause breast cancer. The agency was unable to provide a definitive answer, however, to the question of whether passive smoke inhalation by children in the home is linked to childhood cancers.
Overall, half of all smokers will die prematurely because of their habit. Half of these deaths occur in middle age (35-69 years). Tobacco is the leading cause of preventable cancers worldwide.
The current global trend towards people being younger when they start smoking bodes ill for the future, says the report. Many young Britons and Americans will have been committed smokers for 30 years by the time they reach the age of 40.
The WHO hopes that its report, which updates a previous survey from 1986, will convince governments to act on controlling smoking in public places and to encourage people to stop. "Smoking cessation, along with never starting to smoke, will remain the best ways to prevent cancer around the world in the 21st century," says the paper. "Any possible public health gains from changes in cigarette composition would be minimal in comparison."
The report can be accessed at the agency’s website (www.iarc.fr).
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