Women smokers face a higher risk of bladder cancer than previously thought, according to a US study out Tuesday that points to the changing content of cigarettes as a potential reason for the increase. The latest data shows that smoking is responsible for about half of bladder cancer cases in women, compared to previous studies that showed between 20-30 percent of such cases were attributable to tobacco use. "The stronger association between smoking and bladder cancer is possibly due to changes in cigarette composition or smoking habits over the years," said study author Neal Freedman of the National Cancer Institute (NCI). The research, funded by the US National Institutes of Health and published in the Journal of the American Medical Association, said "the composition of cigarettes has changed during the past 50 years." These changes have led to "a reduction in tar and nicotine concentrations in cigarette smoke, but also to an apparent increase in the concentration of specific carcinogens, including beta-napthylamine, a known bladder carcinogen." Also, more women are smoking than before, which could explain the change. "Men and women are about equally likely to smoke, as observed in the current study and in the US population overall, according to surveillance by the CDC (Centers for Disease Control and Prevention)," said the study. "The majority of the earlier studies were conducted at time periods or in geographic regions where smoking was much less common among women." Previous studies have shown the risk of bladder cancer in current and former smokers was between 50-65 percent in men and 20-30 percent in women, while current smokers face triple the risk of getting bladder cancer as people who never smoked. Tuesday's study shows that smoking is linked to an even higher risk of bladder cancer in women -- 52 percent -- while men stayed about the same at 50 percent. The latest findings appear to confirm a 2009 US study by the NCI that showed a stronger association between smoking and bladder cancer than had been observed in the mid-1990s. "Incidence rates of bladder cancer in the United States have been relatively stable over the past 30 years, despite the fact that smoking rates have decreased overall," said Freedman. "The higher risk, as compared to studies reported in the mid-to-late 1990s, may explain why bladder cancer rates haven't declined." CDC data from 2009 shows that an estimated 46 million people, or 20.6 percent of all US adults, smoke cigarettes, though smoking is slightly more common among men (23.5 percent) than women (17.9 percent). Health authorities say about 69,250 people will be diagnosed with bladder cancer this year in the United States, and 14,990 will die from the disease.