Influence of cardiorespiratory fitness on lung cancer mortality

Abstract

Purpose: Previous studies have suggested that higher levels of physical activity may lower lung cancer risk; however, few prospective studies have evaluated lung cancer mortality in relation to cardiorespiratory fitness (CRF), an objective marker of recent physical activity habits.

Methods: Thirty-eight thousand men, aged 20-84 yr, without history of cancer, received a preventive medical examination at the Cooper Clinic in Dallas, Texas, between 1974 and 2002. CRF was quantified as maximal treadmill exercise test duration and was grouped for analysis as low (lowest 20% of exercise duration), moderate (middle 40%), and high (upper 40%).

Results: A total of 232 lung cancer deaths occurred during follow-up (mean = 17 yr). After adjustment for age, examination year, body mass index, smoking, drinking, physical activity, and family history of cancer, hazard ratios (95% confidence intervals) for lung cancer deaths across low, moderate, and high CRF categories were 1.0, 0.48 (0.35-0.67), and 0.43 (0.28-0.65), respectively. There was an inverse association between CRF and lung cancer mortality in former (P for trend = 0.005) and current smokers (P for trend < 0.001) but not in never smokers (trend P = 0.14). Joint analysis of smoking and fitness status revealed a significant 12-fold higher risk of death in current smokers (hazard ratio = 11.9, 95% confidence interval = 6.0-23.6) with low CRF as compared with never smokers who had high CRF.

Conclusions: Although the potential for some residual confounding by smoking could not be eliminated, these data suggest that CRF is inversely associated with lung cancer mortality in men. Continued study of CRF in relation to lung cancer, particularly among smokers, may further our understanding of disease etiology and reveal additional strategies for reducing its burden.

Figure 1

Kaplan-Meier survival curves for lung cancer mortality by cardiorespiratory fitness (CRF) levels, Aerobics Center Longitudinal Study, Dallas, Texas, 1974–2003.

Figure 2

Multivariate risk for lung cancer mortality by smoking status and fitness level. The height of bars represent hazard ratios adjusted for age, examination year, alcohol use, BMI, physical activity, and family history of cancer.

Figure 3

Multivariate-adjusted hazard ratios for cardiorespiratory fitness (CRF) and lung cancer mortality in a subset of men (N=14,419) who had available data to calculate the pack-years in the Aerobics Center Longitudinal Study. The height of bars represent hazard ratios adjusted for age, examination year, pack-years smoking, alcohol use, BMI, physical activity, and family history of cancer.