The mean ages at baseline and at the end of follow-up were 61.9 (standard deviation (SD), 5.4) and 69.1 (SD, 5.5) years, respectively. At baseline, 18% of the cohort reported not being physically active, and 19% indicated engaging in physical activity 5 or more times per week. Physical activity was positively associated with elements of a healthy lifestyle, including less smoking, lower body mass index, greater dietary intakes of fruit and vegetables, and less consumption of red meat. In addition, active participants were more likely to report a college education and to be married than their less active counterparts ().
Baseline Characteristics in 1995–1996 According to Physical Activity, NIH–AARP Diet and Health Study
Lung carcinoma risk was inversely associated with body mass index and educational level, and it was suggestively inversely related to intakes of fruit and vegetables. In contrast, lung carcinoma risk was positively associated with smoking, family history of cancer, and intakes of red meat and alcohol (data not tabulated).
During 3,600,331 person-years of follow-up (mean follow-up, 7.2 years; SD, 1.4), we documented 6,745 lung carcinoma cases, of which 14.8% were small cell, 40.3% were adenocarcinoma, 19.7% were squamous cell, 6.1% were undifferentiated large cell, 7.2% were non-small cell not otherwise specified, and 11.8% were lung carcinoma not otherwise specified. The risk of total lung carcinoma decreased in a linear fashion with increasing physical activity level (). In analyses that were adjusted for age and gender, participants who reported engaging in physical activity 5 or more times per week had a relative risk of 0.50 (95% confidence interval (CI): 0.46, 0.54; Ptrend
< 0.001) as compared with their inactive counterparts. After additional control for smoking status (current, former, or never smoking), the inverse association was substantially attenuated (relative risk (RR) = 0.68, 95% CI: 0.63, 0.74; not shown in ). When we further adjusted for the combination of smoking intensity and time since quitting, the relation became slightly weaker, but it remained statistically significant (RR = 0.77, 95% CI: 0.71, 0.83). Additional control for other potential confounding variables had little impact. When we examined physical activity in relation to mortality from lung cancer (n
4,793 cases), the multivariate relative risk was 0.79 (95% CI: 0.72, 0.87).
Relative Risk of Total Lung Carcinoma and Histologic Type of Lung Carcinoma According to Physical Activity, NIH–AARP Diet and Health Study, 1995–2003
Undiagnosed lung carcinoma may have caused subjects to report a lower physical activity level at the time the baseline questionnaire was administered, which would bias our results. After we excluded all cases of lung carcinoma that occurred during the first 4 years of follow-up (n
3,260 lung carcinoma cases excluded), results were not materially altered (multivariate RR comparing extreme categories
= 0.82, 95% CI: 0.74, 0.92). Findings were also virtually unchanged when we further minimized any impact that undiagnosed lung carcinoma may have had on physical activity levels by additionally excluding subjects who reported poor health at entry (n
3,392 lung carcinoma cases excluded; RR
0.83, 95% CI: 0.74, 0.93). When we repeated our analysis of excluding the first 4 years of follow-up, this time using mortality from lung cancer as an endpoint, the corresponding relative risk was 0.80 (95% CI: 0.71, 0.93).
Using data from a subcohort of study participants for whom we had a separate assessment of physical activity that included information on light and moderate to vigorous physical activity (n
3,836 cases), we found that both light activity (multivariate RR for >7 hours of activity per week vs. no activity
0.85, 95% CI: 0.76, 0.95) and moderate to vigorous activity (multivariate RR for >7 hours of activity per week vs. no activity
0.82, 95% CI: 0.74, 0.90) were inversely related to lung carcinoma.
We next investigated physical activity in relation to histologic types of lung carcinoma ().As in our analysis of total lung carcinoma, adjustment for smoking accounted for most of the difference between the age- and gender-adjusted models and the multivariate models. Physical activity showed an inverse or suggestively inverse relation with all histologic subtypes. The relative risks for small cell, adenocarcinoma, squamous cell, and undifferentiated large cell carcinomas were 0.82 (95% CI: 0.67, 1.01), 0.80 (95% CI: 0.71, 0.91), 0.78 (95% CI: 0.65, 0.93), and 0.86 (95% CI: 0.62, 1.21), respectively.
When we repeated the histology-specific analyses among cases of fatal lung cancer for which we had both incidence and mortality data, the corresponding relative risks for small cell, adenocarcinoma, squamous cell, and undifferentiated large cell carcinomas were 0.83 (95% CI: 0.66, 1.05), 0.86 (95% CI: 0.73, 1.02), 0.74 (95% CI: 0.59, 0.94), and 0.88 (95% CI: 0.59, 1.32), respectively.
Because lung carcinomas among ever smokers and never smokers may be differentially influenced by physical activity, we conducted additional analyses that were stratified by smoking status (). Increased physical activity was similarly related to decreased risk of total lung carcinoma among both current and former smokers (Pinteraction
= 0.301). In contrast, no relation of physical activity to total lung carcinoma was noted among never smokers, and that null association differed significantly from the inverse relation with physical activity observed among ever smokers (Pinteraction
Table 3. Multivariate Relative Risk of Total Lung Carcinoma and Histologic Type of Lung Carcinoma According to Physical Activity in Participants Defined by Smoking Status, Smoking Intensity, and Time Since Quitting Smoking, NIH–AARP Diet and Health Study, (more ...)
On evaluation of lung carcinoma subtypes by smoking status, we observed a similar pattern of an inverse association with physical activity among current and former smokers and no relation among never smokers for most histologic types, although the difference in the relation of physical activity to lung carcinoma by smoking status (ever vs. never smokers) was statistically significant only for total non-small cell lung carcinoma (Pinteraction
0.006) and, within that group, for adenocarcinoma (Pinteraction
= 0.019) (). For the group of current smokers, the inverse association with physical activity was most apparent for adenocarcinoma.
To evaluate whether the association between physical activity and lung carcinoma was modified by gender, age, race, education, body mass index, history of emphysema, intakes of fruit and vegetables, red meat, and alcohol, and use of nonsteroidal antiinflammatory drugs, we repeated our analyses within subgroups defined by those variables (). Physical activity was related to decreased lung carcinoma risk in almost all subgroups, suggesting no important effect modification (all Pinteraction > 0.05).
Multivariate Relative Risk of Total Lung Carcinoma According to Physical Activity in Participants Defined by Selected Variables, NIH–AARP Diet and Health Study, 1995–2003a