Roxanne Nelson

November 20, 2008

November 20, 2008 — Consumption of cruciferous vegetables might help protect smokers against lung cancer, according to new data. Although cruciferous vegetables are known to confer a protective effect against a number of cancers, this is the first comprehensive study to report a benefit to individuals who are current smokers.

The finding was presented at the Seventh Annual American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research, held in Washington, DC. The study results suggest that the risk of developing lung cancer was reduced by 22% to 50% among smokers who consumed at least 4.5 servings of raw cruciferous vegetables a month, compared with those who consumed less than 2.5 servings per month.

The researchers also observed that the significant inverse association between consumption of cruciferous vegetables and lung cancer was only seen for squamous or small cell carcinoma, which are the 2 subtypes most strongly associated with heavy smoking.

Our study was initiated by strong evidence that there is an inverse association between cruciferous vegetable intake and lung cancer risk, said lead author Li Tang, PhD, a post-doctoral fellow at Roswell Park Cancer Institute, in Buffalo, New York.

Researchers from Roswell Park previously demonstrated that the intake of raw cruciferous vegetables, including broccoli, broccoli sprouts, cabbage, and cauliflower, was associated with a reduced risk for bladder cancer. (Cancer Epidemiol Biomarkers Prev. 2008;17:938-944). The inverse association was significant among current and heavy smokers who consumed 3 or more servings per month of raw cruciferous vegetables. The protective action of cruciferous vegetables is derived at least in part from isothiocyanates, a group of carcinogen-modulating phytochemicals found in these vegetables.

But although the consumption of cruciferous vegetables has previously been shown to be associated with a lower risk for lung cancer, findings stratified by smoking status have remained inconsistent.

In the current study, Dr. Tang and colleagues conducted a hospital-based case–control study that examined 948 patients diagnosed with primary lung cancer between 1982 and 1998, and 1743 healthy controls. Study participants completed questionnaires that detailed their intake of total fruits and vegetables, as well as cruciferous vegetables, along with risk factors for lung cancer, such as cigarette smoking.

"To control for the compounding factors of smoking, we matched case and control for smoking status and further adjusted the data for smoking duration and smoking intensity," said Dr. Tang during a press briefing. "Unlike previous studies, we also took into account whether the vegetables were cooked or raw because we know that cooking can substantially decrease the amount of isothiocyanates," he continued.

After controlling the data for smoking status and other known risk factors, the researchers observed strong linear inverse associations between intakes of fruit, total vegetables, and cruciferous vegetables, and risk for lung cancer (odds ratio range, 0.53 - 0.70; P for trend < .05). An intake of fruits and total vegetables showed a relatively stronger association among never smokers, whereas significant inverse associations with cruciferous vegetable consumption were only observed among smokers and former smokers.

They also noted that, of the 4 histologic subtypes of lung cancer, the risk reduction was only seen for small cell carcinoma and squamous cell carcinoma.

Previous research has found that fruit and vegetables can be protective against lung cancer, but this study provides new information about smoking status and the nature of the fruits and vegetables, commented Elizabeth A. Platz, ScD, MPH, associate professor at Johns Hopkins Bloomberg School of Public Health, in Baltimore, Maryland. "They looked at which vegetables might be the most helpful in preventing lung cancer, and also looked at the histologic types of lung cancer."

The researchers also looked at the relation between fruit and vegetable intake and never smokers. This is important, explained Dr. Platz, "because there are people diagnosed with lung cancer who have never smoked."

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