Physical activity and the risk of lung cancer in Canada.

A population-based case-control study of 2,128 cases with histologically confirmed incident lung cancer and 3,106 population controls aged 20-76 years was conducted to assess the impact of recreational physical activity on lung cancer risk in Canada in 1994-1997. The multivariable-adjusted odds ratios and 95% confidence intervals for the second, third, and fourth quartiles versus the lowest quartile of total recreational physical activity were, respectively, 0.82 (95% confidence interval: 0.68, 0.98), 0.76 (95% confidence interval: 0.63, 0.92), and 0.73 (95% confidence interval: 0.60, 0.89) (p for trend=0.0008). The risk reduction was observed for both men and women and was attributed to both moderate and vigorous activities. A greater risk reduction was found for squamous cell carcinoma in women, small cell carcinoma in men, and other types/unspecified histologic subtypes in both genders. The physical-activity-associated risk reduction was more profound among smokers and those with low and medium body mass indexes. This study provides additional evidence that recreational physical activity reduces lung cancer risk. More studies are needed to confirm the differences between histologic subtypes and between genders and to address the underlying biologic mechanisms.