The majority of epidemiological studies investigating the relationship between physical activity (PA) and lung cancer risk support the role of recreational PA in lung cancer risk reduction. There have been fewer studies that have examined occupational PA in relation to lung cancer risk and inconclusive results have been reported with some evidence supporting a positive association. In most of these studies, the assessment of occupational PA was crude, based either on self-reported cross-sectional assessments or simple job title-based categorizations. Consideration of lifetime occupational PA and occupational PA accrued in different age windows may provide additional information regarding the direction and magnitude of the relationship, as well as the biologically relevant time window, between PA and lung cancer risk.
Methods: The relationship between lifetime occupational PA and lung cancer risk was examined in a population-based case-control study of 1,136 incident lung cancer cases and 1,457 controls conducted in Montreal, Canada. Lifetime job history was collected via in-person interviews; for each job, the main tasks conducted were also obtained. The energy expenditure for each job-related task was determined via expert assessment by an industrial hygienist and an exercise physiologist in units of metabolic equivalent of task (MET). For each job, an average MET value was calculated by weighting the MET values of each job-related task by the hours per week spent in each task. The average lifetime occupational PA level was then computed by weighting the average MET value for each job by the duration spent in that job. The interview also elicited information on the subject's habitual recreational PA.
Unconditional logistic regression was used to estimate adjusted odds ratios (OR) with 95% confidence intervals (CI) for lung cancer risk associated with average lifetime occupational PA and average occupational PA levels in different age windows while controlling for potential confounders. Specifically, average occupational PA in the age windows of 18-24, 24-44 and 45-64 years in relation to lung cancer risk was examined. Confounding was assessed by combining directed acyclic graphs and the change-in-estimate procedure as a novel approach for covariate selection. Effect modification by smoking, body mass index (BMI) and exposure to occupational carcinogens was also assessed. All analyses were conducted separately for men and women.
Results: The OR (95% CI) between average lifetime occupational PA and lung cancer risk, comparing the highest versus lowest quartile, was 1.38 (0.88-2.16) in men and 1.01 (0.58-1.76) in women. These associations were not modified by smoking level, BMI or occupational carcinogen exposure.
Occupational PA in men was not associated with lung cancer in any of the age windows in which exposure was examined. In women, the highest versus lowest quartile of occupational PA was associated with an increased risk of lung cancer in the age window of 18-24 years (OR=1.72: 1.00-2.94); in the age windows of 24-44 (OR=0.89: 0.53-1.48) and 45-64 years (OR=0.63: 0.38-1.02) no increase in lung cancer risk was observed.
When analyses were adjusted for recreational PA, results did not differ appreciably.
Conclusion: These results fail to support the previously reported protective effects of PA on lung cancer risk. To the limited extent that they show a deviation from the null hypothesis of no influence on risk, they actually suggest some increased risk of lung cancer with higher occupational PA, although this relationship was inconsistent between sexes and in different age windows.
This research was funded by the Canadian Cancer Society and the Guzzo-SRC Chair in Environment and Cancer.
Citation Format: Vikki Ho, Marie-Élise Parent, Javier Pintos, Michal Abrahamowicz, Lise Gauvin, Jack Siemiatycki, Anita Koushik. Lifetime occupational physical activity and lung cancer risk in men and women. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A47.