12 November 2018

This article examined the findings from 31 prospective cohort studies of women between 30 and 79 years and involved over 3.3 million women [3]. The authors reported that there was no relationship between BMI and breast cancer risk in premenopausal women; however, in postmenopausal women, breast cancer risk increased by 3.4% for every 1 kg/m2 increment in BMI. When exploring the relationship between BMI and breast cancer further, the authors reported a reduction in risk of breast cancer with increasing BMI in studies of European women (relative risk (RR) 0.79, 95% CI 0.70–0.88) but not in Asian or American women, or the group as a whole. However, in postmenopausal women, higher BMI was associated with higher risks of breast cancer in the group as a whole, Asian women (RR 2.10; 95% CI 1.64–2.69), US women (RR 1.29; 95% CI 1.14–1.46), women with estrogen receptor-positive breast cancer (RR 1.32; 95% CI 1.23–1.42) and those with no past hormone therapy use (RR 1.43; 95% CI 1.21–1.68), but interestingly no increase in risk with increasing BMI in European women (RR 1.19; 95% CI 0.98–1.43) or those with a past history of hormone therapy use (RR 0.94; 95% CI 0.63–1.40).

Comment

Increasingly cancer risk has been linked to lifestyle, and, whilst there are very clear links with regard to obesity and some cancers in women, such as endometrial cancer, the relationship between BMI per se and some cancers is yet to be fully defined. Fat is an endocrinologically active organ, especially with regard to estrogen, and hence a link between increased fat mass and hormonally linked cancers seems logical. These findings are interesting and point to the importance of lifestyle and metabolic factors in breast cancer risk, and also to the role of health practitioners in promoting general health measures such as achieving a healthy weight for height, as a cancer risk reduction strategy.

Sonia Davison

Endocrinologist, Women’s Health Research Program, Monash University, Australia

Reference

Chen Y, Liu L, Zhou Q, et al. Body mass index had different effects on premenopausal and postmenopausal breast cancer risks: a dose-response meta-analysis with 3,318,796 subjects from 31 cohort studies. BMC Public Health 2017;17:936
https://www.ncbi.nlm.nih.gov/pubmed/29216920