Abstract
PurposeThe purpose of the present study was to systematically review the complex associations between energy balance-related factors and breast cancer risk, for which previous evidence has suggested different associations in the life course of women and by hormone receptor (HR) status of the tumor.MethodsRelevant publications on adulthood physical activity, sedentary behavior, body mass index (BMI), waist and hip circumferences, waist-to-hip ratio, and weight change and pre- and postmenopausal breast cancer risk were identified in PubMed up to 30 April 2017. Random-effects meta-analyses were conducted to summarize the relative risks across studies.ResultsOne hundred and twenty-six observational cohort studies comprising over 22,900 premenopausal and 103,000 postmenopausal breast cancer cases were meta-analyzed. Higher physical activity was inversely associated with both pre- and postmenopausal breast cancers, whereas increased sitting time was positively associated with postmenopausal breast cancer. Although higher early adult BMI (ages 18–30 years) was inversely associated with pre- and postmenopausal breast cancers, adult weight gain and greater body adiposity increased breast cancer risk in postmenopausal women, and the increased risk was evident for HR+ but not HR− breast cancers, and among never but not current users of postmenopausal hormones. The evidence was less consistent in premenopausal women. There were no associations with adult weight gain, inverse associations with adult BMI (study baseline) and hip circumference, and non-significant associations with waist circumference and waist-to-hip ratio that were reverted to positive associations on average in studies accounting for BMI. No significant associations were observed for HR-defined premenopausal breast cancers.ConclusionBetter understanding on the impact of these factors on pre- and postmenopausal breast cancers and their subtypes along the life course is needed.
Highlights
Breast cancer is the most frequent cancer and the leading cause of cancer death in women
The Third Expert Report published by the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) concluded that there is strong evidence that vigorous physical activity protects against premenopausal breast cancer, moderate or vigorous physical activity protects against postmenopausal breast cancer, and greater body fatness and weight gain in adult life causes postmenopausal breast cancer [8]
Previous studies have shown that adherence to the 2007 WCRF/AICR recommendations [9] is associated with reduced breast cancer risk [10–17], breast cancer mortality [18] and total mortality [19], and improved cancer survival [20]; signifying the importance of healthy lifestyles
Summary
Breast cancer is the most frequent cancer and the leading cause of cancer death in women. The Third Expert Report published by the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) concluded that there is strong evidence that vigorous physical activity protects against premenopausal breast cancer, moderate or vigorous physical activity protects against postmenopausal breast cancer, and greater body fatness and weight gain in adult life causes postmenopausal breast cancer (https://www.wcrf.org/dietandcancer) [8] These conclusions supported the recommendations for cancer prevention which promote healthy body weight (World Health Organisation definition: 18.5 to 24.9 kg/m2) and adequate energy balance throughout life (be physically active, eat a diet rich in wholegrains, vegetables, fruit and beans, limit consumption of ‘fast foods’ and other processed foods high in fat, starches or sugars, and sugar sweetened drinks). Previous studies have shown that adherence to the 2007 WCRF/AICR recommendations [9] is associated with reduced breast cancer risk [10–17], breast cancer mortality [18] and total mortality [19], and improved cancer survival [20]; signifying the importance of healthy lifestyles
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