Abstract 5316: Recreational physical activity, body mass index, and waist circumference in relation to lung cancer incidence in a large US prospective cohort
Authors: Patel Alpa V. , Carter Brian D. , Stevens Victoria L. , Campbell Peter T. , Gapstur Susan M. 
Published: July 2017

Background: Physical activity has been associated with lower lung cancer risk in numerous studies with estimates ranging from 20-50% lower risk in the most versus the least active study participants. Underweight and obesity have also been associated with lower lung cancer risk, with a nonlinear, inverted U-shaped relationship. The associations between physical activity and obesity with lung cancer are likely significantly confounded by smoking since individuals who smoke are generally less active and leaner than non-smokers. However, few studies have been able to examine these associations stratified by smoking status.

Objective: To examine in detail whether an association between physical activity, BMI, and lung cancer exists in the absence of residual confounding by smoking.

Methods: Using data 118,225 men and women who were cancer-free at enrollment (1992) in the American Cancer Society Cancer Prevention Study-II Nutrition Cohort, we examined associations between recreational physical activity (MET-hours per week; none, 0.1-&lt;8.75 (reference), 8.75-17.4, 17.5+ MET-hours/week), body mass index (BMI, weight (kg)/height (meters)2; &lt;18.5, 18.5-22.0 (reference), 22.1-24.9, 25.0-29.9, 30.0+ kg/m2), and waist circumference (measured in 1997; sex-specific quartiles) in relation to lung cancer risk stratified by smoking status and years since quitting among former smokers (never, current, former &lt;10 years, former, 10-19 years, former 20+ years). Cox proportional hazards modeling was used to compute hazard rate ratios (RR) and 95% confidence intervals (CI) while adjusting for potential confounders.

Results: Follow-up included 2,384,545person-years during which 4,669 men and women were diagnosed with lung cancer (453 among never smokers; 1,452 among current smokers; 1,194 among former smokers &lt;10 years since quitting; 725 among former 10-19 years; and 845 among former 20+ years). Physically activity was not associated with lung cancer risk for any of the smoking strata except in former smokers less than 10 years since quitting (RR=0.78; 95% CI 0.68-0.91 for 17.5+ MET-hours/week). Similarly, BMI was inversely associated with lung cancer only in former smokers less than 10 years since quitting (RR=0.74; 95% CI 0.60-0.92 for 30+ kg/m2). Waist circumference was not associated with lung cancer risk in any smoking category.

Conclusion: While being physically active and maintaining a healthy body weight are important for prevention of various types of cancer, our results suggest that neither physical activity, body mass index, or waist circumference are associated with lung cancer risk, regardless of smoking status. Whether the associations between physical activity, BMI and lung cancer in ex-smokers who have recently quit are due to chance, confounding or reverse causality warrants further investigation.

Citation Format: Alpa V. Patel, Brian D. Carter, Victoria L. Stevens, Peter T. Campbell, Susan M. Gapstur. Recreational physical activity, body mass index, and waist circumference in relation to lung cancer incidence in a large US prospective cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5316. doi:10.1158/1538-7445.AM2017-5316