Is there link between occupational physical activity levels and lung cancer? A case-control study in Canadian men

Abstract

Background/Aim Many studies have looked at the association between daily physical activity levels and risk of lung cancer, but very little research has been conducted where occupational physical activity (OPA) levels are isolated from recreational physical activity levels. As Canadian jobs are becoming increasingly sedentary, and Canadians spend roughly 50% of their waking day at work, this is a concern. The purpose of this study was to determine whether a link exists between occupational physical activity levels and risk of lung cancer in Canadian men. Methods This study used National Enhanced Cancer Surveillance System (NECSS) data, a questionnaire-based case-control study conducted across eight Canadian provinces between 1994 and 1997. Cases of lung cancer were identified using provincial cancer registries and controls were selected from a random sample from the same province and with a similar age and sex distribution as that of the cancer cases. Occupational physical activity levels were defined by the Canadian Classification and Dictionary of Occupations (CCDO), which includes ancillary information on occupational physical activity scores in categories of sedentary, light, moderate, heavy, and very heavy physical activity. Analysis was conducted using last job held. Basic descriptive statistics were calculated to compare cases and controls as part of a preliminary analysis. SAS software was used to fit categorical linear models to the response frequencies. Results The NECSS data includes information on 1682 male lung cancer cases and 2054 male controls. For analysis purposes very heavy OPA and heavy OPA were combined due to small sample sizes. Overall, workers fell into four categories; heavy OPA (16%), moderate OPA (35%), light OPA (31%), and sedentary OPA (17%). The remaining 1% of workers had unknown OPA and were excluded from further analysis. Further stratification for smoking status showed similar distributions across OPA categories. Of cases who never smoked, 2% worked heavy OPA jobs, 1% worked moderate OPA jobs, 3% worked light OPA jobs, and 3% worked sedentary OPA jobs. Of cases who are ex-smokers 80% worked heavy OPA jobs, 80% worked moderate OPA jobs, 80% worked light OPA jobs, and 83% worked sedentary OPA jobs. Of cases who currently smoke, 18% worked heavy OPA jobs, 19% worked moderate OPA jobs, 17% worked light OPA jobs, and 14% worked sedentary OPA jobs. A main effects model yielded statistically significant results for OPA (P Conclusion We found some evidence that occupational physical activity levels are associated with an increased risk of lung cancer among Canadian males. Further analyses should consider other covariates and modelling interactions.