Energy balance-related factors: epidemiologic evidence for deriving recommendations for breast cancer prevention and survival

Abstract

Background There is evidence that diets and active lifestyle that allows adequate body weight contribute to breast cancer prevention. It is important to keep the evidence base updated to inform lifestyle recommendations and provide useful guidance. Methods As part of the work for the World Cancer Research Fund (WCRF) International Continuous Update Project, the accumulated evidence from cohort studies and randomised controlled trials on energy balance-related factors (total energy intake, physical activity and adiposity) and risk of female breast cancer development and mortality after breast cancer, was systematically reviewed and meta-analysed. The evidence was graded (convincing, probable, limited) and compared with the conclusions published in the 2007 WCRF Second Expert Report. Results Overall, 230 publications were meta-analysed. Higher body fatness, as indicated by body mass index (BMI), and adult weight gain, convincingly increased (12% per 5 kg/m2 and 7% per 5 kg, respectively); and recreational and vigorous physical activity probably reduced (12% and 10% for high vs low levels) postmenopausal breast cancer risk. Evidence on abdominal and gluteofemoral fatness (waist and hip circumferences, waist-hip-ratio) supports these findings. As reported previously, BMI was inversely associated with premenopausal breast cancer risk. Physical activity remains graded limited suggestive, but new findings on vigorous physical activity suggested probable protection (21% for high vs low levels) against breast cancer in premenopausal women. Evidence from studies on breast cancer survivors was limited, but suggested that women with normal body weight and with higher levels of physical activity may have the most favourable survival after breast cancer. Conclusion The new accumulated evidence is consistent with the previous WCRF conclusions, and supports the recommendations for women to aim to have normal body weight (BMI 18.5-24.9 kg/m2) and be physically active (≥ 30 minutes/day moderate-vigorous activity), and to prevent gain in weight and waist circumference. Breast cancer survivors may potentially benefit by following these recommendations after cancer treatment.