Influence of Cardiorespiratory Fitness on Lung Cancer Mortality
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.
Physical inactivity is associated with an increased overall risk of cancer mortality and mortality associated with specific anatomic sites such as colon and breast. However, there is little information regarding the association of inactivity and lung cancer, which is the most common cause of cancer death in the United States. According to the most recent report from the American Cancer Society, in 2009, an estimated 116,090 new cases of lung cancer will be diagnosed, and approximately 88,900 men are expected to die from this disease. Cigarette smoking is the most important cause of lung cancer. Still, many nonsmokers die of the disease, and former smokers remain at elevated risk after quitting. It is estimated that in the United States alone, about 3000 lung cancer deaths occur each year in nonsmoking adults. It takes up to 20 yr for a majority of former smokers' rates to drop to those of never smokers. Therefore, it is plausible that other factors besides smoking may play an important etiologic role. Moreover, the majority of cigarette smokers do not develop lung cancer, and this fact adds to the likelihood that there may be other factors besides smoking that modify risk. One of these other factors might be physical activity.
Most previous cohort studies have reported an inverse association between risk of lung cancer and physical activity in men; however, some have not. These inconsistent findings may be due partly to the measurement errors inherent in self-reported physical activity. Cardiorespiratory fitness (CRF), an objective and a more reproducible measure that reflects the functional consequences of physical activity habits, may provide a better exposure with which to evaluate associations with lung cancer risk. To the best of our knowledge, only one study has been conducted on CRF and lung cancer mortality among men. However, this study examined only men with prediabetes and diabetes. To address cancer prevention strategies, it is important to investigate whether physical activity or CRF reduces cancer incidence or mortality in the general population prospectively. The objective of this report is to examine the risk of lung cancer mortality across levels of fitness, obtained by maximal exercise test on a treadmill, in a large cohort of men from the Aerobics Center Longitudinal Study (ACLS).
Abstract and Introduction
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.
Introduction
Physical inactivity is associated with an increased overall risk of cancer mortality and mortality associated with specific anatomic sites such as colon and breast. However, there is little information regarding the association of inactivity and lung cancer, which is the most common cause of cancer death in the United States. According to the most recent report from the American Cancer Society, in 2009, an estimated 116,090 new cases of lung cancer will be diagnosed, and approximately 88,900 men are expected to die from this disease. Cigarette smoking is the most important cause of lung cancer. Still, many nonsmokers die of the disease, and former smokers remain at elevated risk after quitting. It is estimated that in the United States alone, about 3000 lung cancer deaths occur each year in nonsmoking adults. It takes up to 20 yr for a majority of former smokers' rates to drop to those of never smokers. Therefore, it is plausible that other factors besides smoking may play an important etiologic role. Moreover, the majority of cigarette smokers do not develop lung cancer, and this fact adds to the likelihood that there may be other factors besides smoking that modify risk. One of these other factors might be physical activity.
Most previous cohort studies have reported an inverse association between risk of lung cancer and physical activity in men; however, some have not. These inconsistent findings may be due partly to the measurement errors inherent in self-reported physical activity. Cardiorespiratory fitness (CRF), an objective and a more reproducible measure that reflects the functional consequences of physical activity habits, may provide a better exposure with which to evaluate associations with lung cancer risk. To the best of our knowledge, only one study has been conducted on CRF and lung cancer mortality among men. However, this study examined only men with prediabetes and diabetes. To address cancer prevention strategies, it is important to investigate whether physical activity or CRF reduces cancer incidence or mortality in the general population prospectively. The objective of this report is to examine the risk of lung cancer mortality across levels of fitness, obtained by maximal exercise test on a treadmill, in a large cohort of men from the Aerobics Center Longitudinal Study (ACLS).