By now, it’s obvious that smoking can lead to disease, and that eating a diet rich in fruits and vegetables can protect against disease. Now researchers have discovered that natural chemicals in fruits and vegetables, as well as in wine and tea, might protect smokers against one disease in particular—lung cancer.
A team of researchers in California investigated the effects of natural plant components called flavonoids in 558 people with lung cancer and 837 people without lung cancer. Researchers interviewed the participants about their history of smoking, diet, and other cancer risk factors and compared these factors between lung cancer cases and healthy controls.
Smokers who had high levels of certain flavonoids had a lower risk of developing lung cancer, the researchers reported in the journal, Cancer. This is a particularly significant finding, considering that smoking is implicated in up to 90 percent of lung cancer cases, according to Zuo-Feng Zhang, MD, PhD, Professor of Epidemiology at the UCLA School of Public Health and Jonsson Comprehensive Cancer Center.
Smokers who ate three servings of vegetables, drank tea, and had a glass of wine each day had a lower risk of lung cancer than those who didn’t incorporate these components into their diets. Among the flavonoids that appeared to be most beneficial were catechin (found in green tea, black tea, red wine, strawberries), quercetin (found in apples, onions, beans), and kaempferol (found in red wine, apples, Brussels sprouts).
Flavonoids appear to protect against lung cancer in several ways: they prevent cancer cells from multiplying, trigger a process of programmed cancer cell death (apoptosis), block the formation of blood vessels that feed tumors, and inhibit the action of highly unstable oxidative molecules in the body called free radicals, among other functions.
The reason flavonoids affected lung cancer development in smokers but not in non-smokers might be that their antioxidant properties work specifically on the type of damaging molecules created by tobacco smoking. “Smoking results in increased oxidative stress and DNA damage, leading to lung cancer, and flavonoids’ antioxidant function may reduce the damage from tobacco smoking,” according to Dr. Zhang.
Why certain flavonoids are more protective against lung cancer development than others is still unknown. “Our results will encourage laboratory scientists to work on cell lines and animal models to find out why some flavonoids can, and some can’t protect against cancer development among smokers,” Dr. Zhang says. His team will also investigate which types of vegetables, and how many servings might offer the greatest protection against lung cancer.
Because this is the first study to document the effects of flavonoids on lung cancer, more research is needed before any real health recommendations can be made. However, it’s very clear from this and past research that quitting smoking, avoiding passive smoking, and eating a diet rich in fruits and vegetables may be a good way to protect against lung cancer, as well as other diseases.
Cui Y, Morgenstern H, Greenland S, Tashkin DP, Mao JT, Cai L, Cozen W, Mack TM, Lu QY, Zhang ZF. Dietary flavonoid intake and lung cancer – a population-based case-control study. Cancer. Published online March 7, 2008.