Experts have known for some time that cigarette smoking causes a variety of cancers. A new analysis points to smoking as the cause of about half of all cases of bladder cancer in both men and women, more than previously believed.
More than 350,000 people around the world are diagnosed each year with cancer of the bladder, the organ in the lower abdomen that stores and releases urine.
A 2009 study of smokers in the U.S. state of New Hampshire caught the attention of Neal Freedman, a scientific investigator at the U.S. National Cancer Institute. He and colleagues noticed an unusually high number of cases of bladder cancer attributed to smoking.
They investigated the connection further by analyzing data collected on 500,000 people taking part in the National Institutes of Health's Diet and Health Study. Participants in the long-term study, which began in 1995, were between the ages of 50 and 71 at the start.
When Freedman looked at follow-up data on the participants gathered in 2006, he found that 4,500 of the men and women had developed bladder cancer.
“In our study, current smokers had four times the risk of bladder cancer than never-smokers. And this was higher than observed in previous cohorts which were established in earlier time periods... between the 1960s, 70s and 80s," he said.
Freedman says in those earlier studies of cohorts, or participants, smokers' risk of bladder cancer was just three times higher. “The other interesting finding that we saw was that smoking explained approximately fifty percent of bladder cancer in both men and women in our study. Previous studies were performed in populations where women smoked less than men. And in those studies smoking explained about 50 percent of bladder cancer in men but only between 20 and 30 percent in women," he said.
In addition, Freedman says the composition of cigarettes has changed since the 1960s. While levels of tar and nicotine have been reduced, the researcher says it appears there’s been an increase in a number of known cancer-causing chemicals, including beta napthylamine, which has been linked to bladder cancer.
The new study also found an increased risk of bladder cancer in former smokers.
An article featuring the bladder cancer study is published in the Journal of the American Medical Association.