Women who are relatively young when they go through menopause seem to be at increased risk of developing bladder cancer, researchers from the University of Minnesota School of Public Health in Minneapolis report.

Bladder cancer is quite common in the U.S., representing about 6 percent of all new cancer cases among men and 2 percent among women, Anna E. Prizment and colleagues point out in the International Journal of Cancer. It’s well known that smoking and chemical carcinogens increase the risk, and that it goes up with age.

The researchers looked for factors associated with bladder cancer in a study of 37,459 women between the ages of 55 and 69 years from Iowa. The women were initially free from cancer in 1986, and they were followed through 2003.

During follow-up, a total of 192 women (0.5 percent) were diagnosed with bladder cancer at an average age of 73 years. After factoring in age and smoking, the data showed that the likelihood of developing bladder cancer went up as a woman’s age at menopause went down.

The odds of bladder cancer were 32 percent higher for women who reached menopause between 43 and 47 years, compared with women who reached menopause at age 48 or later. The risk was 60 percent higher for women who were menopausal at 42 or younger. These associations were the same whether menopause occurred naturally or as a result of surgery.

The chances of developing bladder cancer were not linked to any other reproductive factor, including age when periods began, age at first birth, number of births, hormone replacement therapy use, infertility, fibroids, ovarian cysts or endometriosis.

It has been suggested that the drop in estrogen after menopause “could lead to an increased number of urinary tract infections associated with bladder cancer,” Prizment told Reuters Health. “This may explain why we observed associations between bladder cancer and only those reproductive factors which were related to menopause.”

However, Prizment added: “It is too early to make any definite conclusions since the biological mechanism of this association is unclear.”

SOURCE: International Journal of Cancer, March 2007.