Green Salad, Gardening and Lung Cancer

Focused on Health - November 2008

By Rachel Winters

Researchers have found that eating at least four servings a week of green salad and working in the garden once or twice a week can significantly reduce your risk of developing lung cancer – whether you smoke or not.

“This is the first risk prediction model to examine the effects of diet and physical activity on the possibility of developing lung cancer,” said the lead author of the study, Michele R. Forman, Ph.D., a professor in  M. D. Anderson’s Department of Epidemiology and a nutritional epidemiologist.

The study findings are meaningful for the public because the resulting recommendations are seemingly easy to meet. Consuming four salads a week is tasty and affordable, and gardening is an enjoyable pastime that can help you relax and enhance your quality of life.

The study followed 3,800 people from three distinct groups: people who have never smoked, former smokers and current smokers. Participants were comprised of newly diagnosed lung cancer patients and healthy people from Kelsey-Seybold clinic, a Houston-based HMO.

Study results showed that never smokers who consumed three or fewer servings of salad per week increased their risk of developing lung cancer by 200%. Former smokers increased their risk by 250%, and current smokers showed a 270% increase.

An interesting element of the study was that while vegetable consumption has been linked to disease prevention overall, increasing your general vegetable intake was not, in fact, shown to decrease your risk of developing lung cancer. It seems that only the rich mix of phytochemicals in a green salad influences lung cancer risk.

“Salad is the key food in this study because it’s made-up of a multitude of phytochemicals and antioxidants that can prevent cancer,” said Forman.

Phytochemicals come from plants and have health-promoting properties that have been proven to enhance the immune system. Some of the different phytochemicals that can be found in a colorful salad include folate, which is found in dark green leafy vegetables such as spinach, turnip greens and lettuces, and lycopene, which is known for its presence in tomatoes.

Antioxidants, which can be found in a variety of fruits and vegetables, are substances or nutrients that, in some cases, may prevent or slow damage to the lungs from smoking or other sources. When cells use oxygen, they naturally produce by-products that can cause damage. Antioxidants combat these products and may prevent and repair damage done to the lungs. Antioxidants also have been proven to enhance the immune system and help DNA repair the lungs.

For the gardening component of the study, research showed that people who had never smoked could decrease their lung cancer risk by 50 percent by gardening once or twice a week. Spending the same amount of time in the garden decreased cancer risk for former smokers by 45 percent, and individuals who were smokers saw a 40 percent decrease.

While gardening was the one specific type of physical activity associated with a decrease in lung cancer risk, it is not necessarily the only active, outdoor behavior that might be beneficial in the fight against lung cancer. Gardening was specifically identified as having risk reduction potential in this study because it was the physical activity that most study participants had in common, making it the only activity with conclusive data.

“Gardening results are less clear for interpretation because the activity includes a range of behaviors,” said Forman. “Its benefits could be due to sun exposure and vitamin D, or to the actual exercise. Future research needs to examine exactly what components of gardening led to lung cancer risk reduction.”

Forman’s study, funded by the National Cancer Institute, was based on a larger case-control study and lung cancer risk prediction model conducted by Margaret R. Spitz, M.D., M.P.H.,professor and former chair of M. D. Anderson’s Department of Epidemiology. In 2007, Spitz developed one of the only existing lung cancer risk prediction models in the United States, which is currently published in the Journal of the National Cancer Institute.

Forman plans to extend her study by doing further research on physical activity. She also plans to analyze how alcohol consumption might affect lung cancer risk prediction. Spitz and colleagues are looking at the role of genetics and ethnic background as potential risk predictors for lung cancer.

“The bottom line for now, however, is to eat a balanced diet including salad, and to get some outdoor exercise,” said Forman. “The other obvious and clearest predictor of lung cancer is smoking. Stop smoking if you do, and don’t even think about starting if you don’t.”