Broccoli may not fight lung cancer in non-smokers

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NEW YORK: Some studies have hinted that eating your broccoli might help prevent lung cancer. But a new study of non-smoking women finds no strong link between compounds found in cruciferous vegetables such as broccoli and lower risk of lung cancer.

The study, of nearly 1,000 non-smoking Chinese women with and without lung cancer, found no overall association between the women's risk of the cancer and their urinary levels of isothiocyanates -- compounds in cruciferous vegetables thought to have anti-cancer properties.

The results, reported in the journal Lung Cancer, conflict with those of some previous studies finding that among smokers and non-smokers alike, people who eat more cruciferous vegetables tend to have a lower lung cancer risk than those who shun the vegetables.

However, those studies do not prove that the vegetables -- which include broccoli, Brussels sprouts, cauliflower, cabbage and turnips -- are themselves protective. In addition, some research has suggested that if the veggies do offer a benefit, it may vary according to people's genetic make-up.

Specifically, studies have implicated variations in certain genes that govern the activity of GST enzymes, which, among other jobs, help regulate isothiocyanate levels in the body.

Isothiocyanates, or ITCs, trigger an increase in antioxidant enzymes that help counter cell damage and inflammation brought on by oxidative stress -- from sources like air pollution and tobacco smoke. Because cruciferous vegetables are the main dietary source of ITCs, researchers have speculated that the compounds may explain the connection between high consumption of the vegetables and lower lung cancer risk.

For the current study, researchers led by Dr. Jay H. Fowke, of Vanderbilt University Medical Center in Tennessee, used data from a large health study following 75,000 Shanghai women between the ages of 40 and 70.

The researchers focused on 209 non-smoking women who were diagnosed with lung cancer after the study's start. They matched each woman with several other women the same age who remained cancer-free.

When the researchers divided the women into four groups based on ITC levels -- measured from urine samples collected at the study's outset -- they found no overall relationship between the compound and lung cancer risk. That was true regardless of factors like the women's age and exposure to secondhand smoke.

There were some hints that variations in the women's GST genes made a difference. Among women who carried one or two copies of the gene GSTM1, those with higher ITC levels showed a lesser lung cancer risk -- but the difference did not reach statistical significance, which raises the possibility that it was just a chance finding.

On the other hand, among women who carried no copies of GSTM1, lung cancer risk tended to climb in tandem with ITC levels -- though, again, the statistical significance of that finding was not strong.

According to Fowke's team, the results call for continuing research into the relationship between cruciferous vegetables and lung cancer risk, and the role, if any, of GST or other genes.

Among the limitations of this study, they note, is the fact that the women were followed for only three years, and its reliance on a one-time measurement of ITC levels -- which would reflect cruciferous-vegetable intake over only the previous 8 to 72 hours.

Smoking is clearly the major risk factor for lung cancer, and quitting -- or preferably never starting -- remains the primary lifestyle measure for preventing the disease.

However, Fowke and his colleagues point out, about one-quarter of lung cancer cases worldwide are diagnosed in people who have never smoked. So it is important to identify any other modifiable risk factors for the disease.

Regardless of whether cruciferous vegetables have an effect on lung cancer risk, they are considered a healthy diet choice. The American Cancer Society and other medical groups recommend that adults eat at least five servings of vegetables and fruit each day in order to curb their risk of chronic diseases.