AACR Prevention: Raw Cruciferous Vegetables Cut Bladder Cancer Risk


PHILADELPHIA, Dec. 6 -- Uncooked broccoli or other cruciferous vegetables significantly reduce the risk of bladder cancer, epidemiologists said here today.
Action Points --->
Explain that the study found that nonsmokers who ate three or more servings per month of raw broccoli, cauliflower, or cabbage had a reduced risk of developing bladder cancer.
Point out that this was a case-control study, not a randomized, prospective trial, so that a direct cause-and-effect relationship cannot be proven.
This study was published as an abstract at a conference. These data and conclusions should be considered to be preliminary as they have not yet been reviewed and published in a peer-reviewed publication.
The greatest benefit was for nonsmokers who consumed three helpings per month or more, they said.
So it appeared from a hospital-based, case-control study of 275 patients with bladder cancer and 825 age- and sex-matched people without cancer, Susan McCann, Ph.D., of Roswell Park Cancer Institute in Buffalo, N.Y., and colleagues reported at the American Association for Cancer Research's prevention conference.
"We observed a strong and statistically significant inverse association between bladder cancer risk and raw cruciferous vegetables," said Dr. McCann.
The adjusted odds ratio for developing bladder cancer for the most frequent consumers of raw cruciferous vegetables versus the least frequent was 0.64 (95% CI: 0.42 to 0.97), Dr. McCann said. The protective effect of raw cruciferous vegetables was greatest in nonsmokers claiming three or more servings per month (adjusted odds ratio: 0.27, 95% CI: 0.13 to 0.56).
From 1982 through 1998, the participants completed questionnaires on demographics, lifestyle factors such as alcohol and tobacco use, occupation, medical history, reproductive status (women only), and the frequency with which they consumed different kinds of foods in the past.
"This particular questionnaire asked about both raw and cooked vegetables [separately]," said Dr. McCann. Most food consumption surveys don't distinguish between cooked and uncooked foods, she noted.
Li Tang, M.D., Ph.D., of Roswell Park, a co-investigator, said cooking reduces availability of isothiocyanates, the compounds in cruciferous vegetables thought to be responsible for the protective effect.
The participants estimated their consumption of specific raw and cooked cruciferous vegetables, including broccoli, cauliflower, and cabbage, as well as total fruits, total vegetables, and total cruciferous vegetables (cooked and uncooked combined).
The study found no association with bladder cancer occurrence for any food category other than raw cruciferous vegetables.
The dose-response trend toward decreased bladder cancer incidence with increasing frequency of eating raw cruciferous vegetables was clearly significant (P=0.003), Dr. McCann said.
Bladder cancer patients reported eating raw cruciferous vegetables 4.5 times per month on average prior to their diagnosis, she said, whereas the frequency for controls was 5.9 per month.
Dr. McCann noted that, while nonsmokers appeared to get the most benefit from raw cruciferous vegetables, "we also saw a protective effect for heavy smokers."
Smokers with lifetime exposure of more than 33 pack-years showed a 40% reduction in bladder cancer risk with high consumption of raw cruciferous vegetables, Dr. McCann said.
Among all current smokers, she added, the risk reduction with high raw cruciferous vegetable intake was 50%.
Dr. McCann said that participants' actual consumption of particular foods may differ from what they reported because they were recalling what they ate years earlier.
"You can't really estimate exact nutrient intake," Dr. McCann said. "But you can rank people, so you can get an idea of who is high or low in a certain food group or a certain nutrient intake. That will allow you to estimate associations with disease."
She said the group's epidemiological results were in line with experimental data showing extracts from cruciferous vegetables to block cancer development in cell lines and animal models.
The study was funded by the National Cancer Institute.
No conflicts of interest were reported.
Primary source: American Association of Cancer Research: PreventionSource reference:Tang L, "Consumption of raw, but not cooked, cruciferous vegetables and reduction of bladder cancer risk" AACR Prevention Meeting 2007.