Leisure-time physical activity and lung cancer: a meta-analysis

Objective: Several studies have evaluated the relationship between physical activity and lung cancer. To summarize and review these studies, we conducted a meta-analysis of all relevant reports published from 1966 through October 2003. Method: Adjusted odds ratios (ORs) from the original studies were pooled by the inverse of their variance, and all pooled estimates were accompanied by an assessment of heterogeneity across investigations. Test for linear trend across activity categories (low, moderate, high) were applied. Results: The combined ORs were 0.87 (95 confidence interval=0.79-0.95) for moderate leisure-time physical activity (LPA) and 0.70 (0.62-0.79) for high activity (ptrend=0.00). This inverse association occurred for both sexes, although it was somewhat stronger for women. No evidence of publication bias was found. Several studies were able to adjust for smoking, but none adjusted for possible confounding from previous malignant respiratory disease. Our simulations suggest that this condition is unlikely to entirely explain the inverse association. Conclusion: The findings of this meta-analysis indicate that higher levels of LPA protect against lung cancer. The inverse association is possible remains confounded by inadequately controlled smoking patterns. However on the whole, confounding seems an unlikely explanation for the findings of individual studies on non-smokers.