'Comfort stops' may have cancer benefits.

Urinating frequently may reduce your change of developing bladder cancer, particularly if you smoke, according to a new study of dogs.

Beagles that urinated every four hours had one-third the cancer-causing substances in the bladder lining compared with a beagle that voided only every eight hours, reports a team led by Fred F. Kadlubar of the National Center for Toxicological Research in Jefferson, Ark., which included scientists from MIT. The findings appear in the Aug. 15 CANCER RESEARCH.

The investigators gave each of four beagles a pill containing 4-aminobiphenyl (ABP), a chemical prevalent in cigarette smoke. They continuously drained one beagle's bladder through a catheter, and allowed the other three to urinate normally. Two of these dogs voided every four hours on average; the third urinated every eight hours.

In early work, Kadlubar and his co-workers had shown that the liver breaks down ABP into a carcinogen that eventually forms cancer-causing adducts, which result when a chemical bonds to DNA. The new study, they say, demonstrates that the adducts from in cells of the bladder wall once the ABP carcinogen is filtered from the blood by the kidneys, and accumulates in urine stored inside the bladder.

"Exposure to [the ABP carcinogen] is directly proportional to the length of time the urine resides in the bladder," they report. They also suggest that other carcinogens may act on the bladder through a similar pathway. Further, because bladder cancer in dogs mirrors the disease in humans, the team concludes that "the frequency of urination should be a critical determinant in human urinary bladder carcinogenesis."