This issue of Life Extension Update reports yet another significant finding concerning the effect of nutrition on the risk of cancer presented at the Frontiers in Cancer Prevention Research conference. The research concerns a protective effect for cruciferous vegetables that is specific to smokers. Cruciferous vegetables, which include broccoli, cabbage, cauliflower, Brussels sprouts and kale, have been shown to provide protection against several types of cancer, yet the current research is the first comprehensive study to demonstrate a protective effect for the vegetables against lung cancer for smokers and former smokers.
At the American Association for Cancer Research's Seventh Annual International Conference on Frontiers in Cancer Prevention Research, held November 16-18, 2008 in National Harbor, Maryland, Roswell Park Cancer Institute post-doctoral fellow Li Tang, PhD reported the results of a hospital-based study, conducted by Dr Tang and colleagues, which compared lung cancer patients matched for smoking status with control subjects who did not have cancer. Analysis of dietary intake found a strong association between a lower risk of lung cancer and greater consumption of fruit, total vegetables, and cruciferous vegetables. While the intake of fruit and total vegetables had a stronger protective effect among those who had never smoked, the benefit for cruciferous vegetables was found to exist only in smokers. Depending upon the type of cruciferous vegetable consumed, as well as smoking status and duration, smokers experienced a 20 to 55 percent reduction in lung cancer risk. Among current smokers, only raw cruciferous vegetable consumption was found to be protective. When lung cancer subtypes were examined, significant reductions were found for squamous and small cell carcinoma, associated with heavy smoking. Concerning the protective mechanism of cruciferous vegetables in smokers, the authors write that their findings "are consistent with the smoking-related carcinogen-modulating effect of isothiocyanates, a group of phytochemicals uniquely present in cruciferous vegetables."
"Broccoli is not a therapeutic drug, but for smokers who believe they cannot quit nor do anything about their risk, this is something positive," Dr Tang commented. "People who quit smoking will definitely benefit more from intake of cruciferous vegetables."
"These findings are not strong enough to make a public health recommendation yet," Dr Tang added. "However, strong biological evidence supports this observation. These findings, along with others, indicate cruciferous vegetables may play a more important role in cancer prevention among people exposed to cigarette-smoking."
Related Health Concern: Lung cancer
Smokers, ex-smokers, and people who have never smoked should all consume five or more servings of colorful vegetables (including raw, darkly colored, and root vegetables) and fruits daily to achieve serum levels of micronutrients associated with the lowest risk of lung cancer. A diet rich in tomatoes, tomato-based products (containing lycopene), citrus fruits, and carotenoids (lutein, zeaxanthin, beta-cryptoxanthin, and retinol) reduces the risk of lung cancer (Holick CN et al 2002). Egg yolk is a bioavailable source of lutein and zeaxanthin (Johnson EJ 2002). Good food sources of carotenoids are spinach, kale, carrots, cantaloupes, cherries, and sweet potatoes.
Phytoestrogens (plant estrogens) from food sources are associated with a decrease in the risk of lung cancer in both current smokers and people who never smoked, but less so in former smokers. Food phytoestrogens include isoflavones, phytosterols, and lignans. High intake of the lignans enterolactone and enterodiol and use of hormone therapy are associated with a 50 percent reduction in the risk of lung cancer (Schabath MB et al 2005). The soy isoflavone genistein significantly prevented lung tumor formation and cancer metastasis in mice (Menon LG et al 1998). Phytoestrogens are also available as nutritional supplements.
Consumption of green tea by nonsmoking women is associated with a reduced risk of lung cancer, and the risks decrease with increasing consumption (Zhong L et al 2001). Experimental studies consistently show that green tea and its polyphenols (e.g. EGCG) can slow the growth of, and kill, lung cancer cells (Clark J et al 2006).
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