Diet and Exercise Are Key Factors in Determining Lung Cancer Risk

Lisa M. Cockrell

December 10, 2007 (Philadelphia, Pennsylvania) — Smoking is not the only factor to be considered in the determination of a person's risk of developing lung cancer, according to a recent study presented at the American Association for Cancer Research (AACR) 6th Annual International Conference on Frontiers in Cancer Prevention Research. This study, highlighted at an AACR press conference on the effects of lifestyle on cancer prevention, suggested that, in addition to smoking, diet and physical activity are key in determining a person's overall risk of developing lung cancer. This is important, especially when considering that although smoking is the leading cause of lung cancer, approximately 15% of all lung cancers are diagnosed in people who have never smoked.
"The way we live our lives does influence our risk of getting cancer," said Tim Byers, MD, professor of preventative medicine at the University of Colorado, in Aurora, who was not involved in the study. "Choices we make in tobacco use, sun exposure, food, and physical activity all seem to add up to explain half or more of cancer risk in the population."
Recently, a model to predict lung cancer development in never, former, and current smokers was developed. Although this Spitz model showed clear associations with lung cancer development and smoking history, family history of respiratory disease, and exposure to second-hand smoke or dust, the model did not take into account the relative contributions of several other factors. In the current study, presented by Michele Forman, PhD, from the University of Texas MD Anderson Cancer Center, in Houston, fruit and vegetable intake, as well as physical activity, were examined as potential risk factors. According to Dr. Forman, this study was the first risk-prediction model for lung cancer that took into account, in addition to smoking, both diet and physical activity.
Data were obtained from the same people used in the generation of the Spitz model. Participants included lung cancer patients enrolled from the University of Texas MD Anderson Cancer Center and healthy matched controls recruited from a local private-physician clinic group. The controls were matched on age, sex, and smoking status. All study participants were categorized as either never, former, or current smokers.
A 135-point questionnaire modified from the National Cancer Institute was used to gather dietary data for all participants. For lung cancer patients, dietary data were gathered for the 1 year prior to diagnosis; for the healthy controls, data were gathered for the 1 year prior to recruitment. The questionnaire responses were standardized by converting to 2006 USDA food-pyramid guidelines. In additional, level of physical activity was established for the study participants.
Interestingly, the participants who ate fewer than 3 salads per week (or vegetables that were associated with salads, such as carrots) had more than twice the risk of developing lung cancer than those who consumed more than 4 salads per week. Importantly, this was shown to be true regardless of smoking status, although the effect was more dramatic in former and current smokers.
However, fruit consumption was not found to affect the risk for lung cancer. In addition, Dr. Forman emphasized that "all of the vegetables that we did find [that were associated with a decreased risk] were in the raw form, and this is very important because the raw form of vegetables may have higher levels of nutrients than the processed form."
Dr. Forman stated that another factor, physical activity, also reduced the risk for lung cancer across all smoking groups. For this study, the physical activity assessed was gardening, because current smokers rarely engaged in any other type of exercise. Participants who gardened on a weekly basis experienced a 33% to 46% decreased risk for lung cancer development, with those who never smoked showing the most dramatic decrease.
When the newer risk-prediction model, which incorporated both diet and exercise, was compared with the original Spitz prediction model, Dr. Forman said it was found to have "a significant increased improvement." However, she cautioned that this study was preliminary in that it did not take into account the effects of many other food groups, alcohol, or vitamin use. In addition, she suggested that 1 possible explanation for the decreased risk associated with salad consumption and gardening is that these individuals inherently have a preventive lifestyle overall. Future analyses to look closely at other preventive and lifestyle factors might add to this prediction model.
This study was funded by grants awarded from the Flight Attendant Medical Research Institute, the Public Health Service, and the National Cancer Institute and National Institutes of Health.
Sixth Annual International Conference on Frontiers in Cancer Prevention Research: Abstract B143. Presented December 7, 2007.