THURSDAY, Feb. 28 (HealthDay News) -- A concentrated extract of freeze-dried broccoli sprouts reduced bladder tumor development by more than half in laboratory rats, according to a new study.

Researchers said the finding supports human epidemiologic studies indicating that eating broccoli and other cruciferous vegetables is associated with a lower risk of bladder cancer.

"Although this is an animal study, it provides potent evidence that eating vegetables is beneficial in bladder cancer prevention," senior investigator Dr. Yuesheng Zhang, a professor of oncology at Roswell Park Cancer Institute, said in a prepared statement.

It's believed that the protective effect of broccoli and other cruciferous vegetables -- such as cabbage, kale, and collard greens -- is at least partly due to isothyiocyanates (ITCs), a group of phytochemicals with anti-cancer properties.

"The bladder is particularly responsive to this group of natural chemicals," Zhang said.

He and his colleagues tested the freeze-dried broccoli sprout extract in rats given a chemical that induces bladder cancer. One group of rats did not receive the extract, while two other groups of rats were given either a low or high dose of the extract in their food, beginning two weeks before they received the cancer-causing chemical.

An average of about two tumors developed in 96 percent of the rats that didn't receive the extract, compared to an average of 1.39 tumors in 74 percent of the rats that received a low dose of the extract, and an average of .46 tumors in 38 percent of the rats that received a high dose of the extract.

The findings were published in the March 1 issue of the journal Cancer Research.

Broccoli sprouts have about 30 times more ITCs than mature broccoli, and the sprout extract used in this study has about 600 times as much. But Zhang said humans at risk for bladder cancer likely wouldn't have to eat large amounts of broccoli sprouts to achieve protective effects.

"Epidemiologic studies have shown that dietary ITCs and cruciferous vegetable intake are inversely associated with bladder cancer risk in humans. It is possible that ITC doses much lower than those given to the rats in this study may be adequate for bladder cancer prevention," he said.

More information

The American Urological Association has more about bladder cancer.