Weight Training and Risk of 10 Common Types of Cancer.

Introduction: Ample data support that leisure time aerobic moderate to vigorous physical activity (MVPA) is associated with lower risk of at least seven types of cancer. However, the link between muscle-strengthening activities and cancer etiology is not well understood. Our objective was to determine the association of weight lifting with incidence of 10 common cancer types.

Methods: We used multivariable Cox regression to estimate hazard ratios (HR) and 95% confidence intervals (CI) for association of weight lifting with incidence of 10 cancer types in the National Institutes of Health-American Association of Retired Persons Diet and Health Study follow-up. Weight lifting was modeled continuously and categorically. Dose-response relationships were evaluated using cubic restricted spline models. We explored whether associations varied by subgroups defined by sex, age, and body mass index using the Wald test for homogeneity. We examined joint categories of MVPA and weight lifting in relation to cancer risk for significant associations.

Results: After adjusting for all covariates including MVPA, we observed a statistically significant lower risk of colon cancer (Ptrend = 0.003) in individuals who weight lifted; the HR and 95% CI associated with low and high weight lifting as compared with no weight lifting were 0.75 (95% CI, 0.66-0.87) and 0.78 (95% CI, 0.61-0.98), respectively. The weight lifting-colon cancer relationship differed between men and women (any weight lifting vs no weight lifting: HRmen = 0.91; 95% CI, 0.84-0.98; HRwomen = 1.00; 95% CI, 0.93-1.08; Pinteraction = 0.008). A lower risk of kidney cancer among weight lifters was observed but became nonsignificant after adjusting for MVPA (Ptrend = 0.06), resulting in an HR of 0.94 (95% CI, 0.78-1.12) for low weight lifting and 0.80 (95% CI, 0.59-1.11) for high weight lifting.

Conclusions: Participants who engaged in weight lifting had a significantly lower risk of colon cancer and a trend toward a lower risk of kidney cancer than participants who did not weight lift.