TUESDAY, Aug. 16 (HealthDay News) -- Almost half of all bladder cancers can be attributed to smoking cigarettes, and the risk of bladder cancer has increased significantly for smokers in the past three decades, a new study finds.
Smokers now face a four times higher risk of developing bladder cancer than someone who has never smoked. Thirty years ago, that risk was about three times that of never-smokers.
Even smokers who've quit the habit still face an increased risk -- 2.2 times higher -- than people who've never smoked, though the risk lessens with time.
"The best way to prevent bladder cancer is for people not to smoke," said study author Neal D. Freedman, an investigator at the National Cancer Institute. "Our study emphasizes the importance of preventing smoking initiation, or for smoking cessation for those who already smoke."
Results of the study will be published in the Aug. 17 issue of the Journal of the American Medical Association.
More than 350,000 people are diagnosed with bladder cancer each year, according to the study. More than 70,000 of those cases occur in the United States, according to the study. And, although the incidence rates for bladder cancer appear to be remaining stable, the researchers noted that findings from several studies suggested that rates for smokers seemed to be rising.
Tobacco smoking is the most significant risk factor for the development of bladder cancer, and previous estimates were that smoking increased the risk of bladder cancer nearly threefold.
To get a better idea of the current risk, Freedman and his colleagues reviewed data from the National Institutes of Health-AARP Diet and Health Study, which was conducted between 1995 and 2006. The study included 281,394 men and 186,134 women between the ages of 50 and 71. The volunteers lived in one of eight states: California, Florida, Georgia, Louisiana, Michigan, New Jersey, North Carolina and Pennsylvania.
Almost 4,000 men and 627 women were diagnosed with bladder cancer during the study.
The researchers found that current smokers now had four times the risk of developing bladder cancer compared to people who never smoked.
Overall, smoking was attributed to the development of about half of all bladder cancers.
And, the risk of bladder cancer tends to rise with the number of cigarettes smoked, according to Freedman. Even people who smoke one to 10 cigarettes a day have a significantly higher risk of bladder cancer than people who don't smoke, according to the study.
He also noted that while the risk of bladder cancer remains elevated for former smokers, it does go down the longer someone stays off cigarettes.
Freedman said the authors don't know exactly why the risk of bladder cancer has increased for smokers, but they suspect changes in the composition of cigarette smoke. Cigarettes contain less tar and nicotine now, but cigarette smoke is likely have more cancer-causing chemicals such as beta-napthylamine, which is known to cause bladder cancer, suggest the authors.
"Cigarettes may be even more toxic now than they were years ago," said Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society.
"People who consider themselves casual smokers may think they're not getting as many of the bad effects of smoking, but in this study, the impact of smoking increases the risk of bladder cancer dramatically," he pointed out.
Lichtenfeld advised that anyone who smokes should stop, though he acknowledged that doing so isn't easy. "Cigarettes are a very powerful addiction that's difficult to quit."
But, both experts agreed that for preventing bladder and other cancers, as well as for heart health, quitting smoking -- or never starting to smoke -- is one of the best things you can do.
More information
Learn more about bladder cancer from the National Cancer Institute.
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