Physical Activity and Risk of Breast Cancer: A Meta-Analysis of 38 Cohort Studies in 45 Study Reports

• Published in: Value in health Vol. 22; no. 1; pp. 104 - 128
• Main Authors: Chen, Xuyu, Wang, Qiru, Zhang, Yanan, Xie, Qian, Tan, Xiaodong
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.2019; Elsevier Science Ltd
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Analysis; Bias; Body mass index; Breast cancer; Breast Neoplasms - diagnosis; Breast Neoplasms - epidemiology; Breast Neoplasms - prevention & control; Cohort analysis; Cohort Studies; Confidence intervals; Cost analysis; Energy Metabolism; Exercise; Female; Health insurance; Healthy Lifestyle; Humans; Internal Medicine; Low income groups; Medical technology; Meta-analysis; Middle Aged; Physical activity; Post-menopause; Prognosis; Protective Factors; Public Health; Quality assessment; Quality control; Recreation; Risk Assessment; Risk Factors; Risk Reduction Behavior; Sedentary Behavior; Statistical analysis; Systematic review; Time Factors; Workplaces; Young Adult; meta-analysis; breast cancer; systematic review; physical activity
• ISSN: 1098-3015; 1524-4733; 1524-4733
• DOI: 10.1016/j.jval.2018.06.020

To evaluate and quantify the association between physical activity (PA) and risk of breast cancer. A systematic review meta-analysis was conducted. The literature was independently and manually searched by 2 reviewers through 3 English databases (PubMed, Embase, and ISI Web of Science) for data till October 2017. The quality of included studies was assessed by the Newcastle-Ottawa Quality Assessment Scale. Fixed-effects models were used to estimate the pooled relative risk and 95% confidence intervals (95% CI). Dose–response analysis was chosen for quantifying the association between PA and risk of breast cancer. The Begg test and the Egger test were used to estimate potential publication bias. Heterogeneity between studies was evaluated with I2 statistics. The meta-analysis included 38 cohort studies published between 1994 and 2017, which included 68 416 breast cancer cases. The overall relative risk (ORR) for breast cancer was 0.87 (95% CI 0.84-0.90). The inverse association was consistent among all subgroup analyses. In subgroup analysis by menopausal status, the ORR of breast cancer was 0.83 (95% CI 0.79-0.87) for premenopausal status and 0.91 (95% CI 0.85-0.97) for postmenopausal status. In subgroup analysis by PA type, the ORR for total activity was 0.87 (95% CI 0.81-0.93), for recreational activity 0.88 (95% CI 0.85-0.91), for occupational activity 0.91 (95% CI 0.84-0.99), and for nonoccupational activity 0.87 (95% CI 0.83-0.92). The risk of breast cancer was significantly lower in people with exposure periods longer than 1 year and less than 5 years (ORR 0.62; 95% CI 0.46-0.78), followed by those with lifetime activity (ORR 0.81; 95% CI 0.69-0.93). The ORR for subjects with body mass index of less than 25 kg/m2 (0.88; 95% CI 0.83-0.93) was close to that for subjects with body mass index of more than 25 kg/m2 (0.87; 95% CI 0.77-0.97). A linear relationship was found between breast cancer risk and PA (recreational activity and total activity), and the ORR was reduced by 3% (95% CI 0.95-0.99) for every 10 metabolic equivalent of energy hours per week increment in recreational PA and by 2% (95% CI 0.97-0.99) for every 10 metabolic equivalent of energy hours per week increment in total PA. PA is significantly associated with a decrease in the risk of breast cancer. •Many studies found that physical activity (PA) is significantly associated with a decrease in the risk of breast cancer, and so did this study.•We also quantified the effect of PA, and so a dose–response analysis was chosen in our study.•All the studies we included were cohort studies, which could reduce bias.•To study the relationship between PA and breast cancer risk, which has a positive effect on breast cancer prevention.