Physical Activity and Weight Loss Reduce the Risk of Breast Cancer: A Meta-analysis of 139 Prospective and Retrospective Studies.

BACKGROUND: Physical activity and weight loss have been shown to reduce breast cancer incidence in numerous observational studies. The aim of this meta-analysis was to assess the effect of both physical activity and weight loss on breast cancer incidence. Specifically, we aimed to complete subgroup analyses by the intensity of physical activity and menopausal status at breast cancer diagnosis to further elucidate the relationship between physical activity, weight loss, and breast cancer incidence.

MATERIALS AND METHODS: Studies were obtained from a database search of MEDLINE, EMBASE, PubMed, Current Contents Connect, and Google Scholar through November 5, 2017. A random-effects model was used for pooled data.

RESULTS: There were 139 studies included in the meta-analysis, including 236,955 cases and 3,963,367 controls. Physical activity significantly reduced the risk of breast cancer (odds ratio [OR], 0.78; 95% confidence interval [CI], 0.76-0.81; P < .001), with high-intensity physical activity being slightly more protective (OR, 0.73; 95% CI, 0.65-0.81; P < .001) than low-intensity exercise (OR, 0.79; 95% CI, 0.72-0.86; P < .001). The effect size for general exercise was similar in both premenopausal (OR, 0.79; 95% CI, 0.73-0.87; P < .001) and postmenopausal (OR, 0.82; 95% CI, 0.78-0.86; P < .001) women. Additionally, weight loss reduced the risk of breast cancer incidence (OR, 0.82; 95% CI, 0.67-0.97).

CONCLUSION: Physical activity and weight loss significantly reduce the risk of breast cancer, irrespective of the timing and intensity of the exercise.