SCIENCE BLOG: Alcohol and excess weight linked to breast cancer risk
Published 29 Mar 2018
A new UK study published last week in the British Journal of Cancer found that around a sixth of all breast cancer cases in the UK in 2015 were attributable to alcohol or excess weight (1). Crucially, it estimated that 38% of all cancers and 23% of breast cancers were preventable. This represents around 12,700 breast cancer cases out of around 55,000 cases diagnosed in the UK in 2015. The study carried out by Cancer Research UK is something we welcome here at Breast Cancer UK – because it reaffirms our belief that a significant number of breast cancers can be prevented.
The research found that alcohol could have been responsible for 8% of all breast cancers, with excess weight (“overweight/obesity”) responsible for 8.3%. That adds up to around 9000 breast cancer cases that might perhaps have been avoided. Other modifiable risk factors included never having breast fed (4.7%), use of hormone replacement therapy (2.1%) and use of oral contraceptives (0.8%). ‘Exposure to ionising radiation’, which includes exposure to naturally occurring radon, X-rays and radiotherapy, was estimated to be responsible for 1.5% of breast cancers (around 825 breast cancer cases).
One surprising element of the research was the finding that a lack of physical activity did not contribute to breast cancer. Yet an earlier paper by one of the authors (2) and many other studies have concluded that low levels of physical activity are associated with increased risk of breast cancer, and in general, the more activity the greater the reduction in risk (e.g. 3, 4, 5, 6). The positive effects of exercise are many; for example it can help to reduce weight loss and reduce concentrations of endogenous hormones, including oestrogen (7, 8) – so we don’t recommend you give up the exercise routine just yet!
We were disappointed but unsurprised that exposure to environmental chemicals such as those found in plastics, pesticides, cosmetics and packaging were not considered as possible risk factors. More surprising however, was that the research did not consider the contribution of shift work to breast cancer risk. Although the role of shift work (and light at night) in increasing breast cancer risk is unclear, with different meta-studies arriving at different conclusions (e.g. 9 and 10), it is disappointing that this study did not include an assessment of this potential risk factor.
Breast cancer has numerous risk factors, and many of these are outside of our control – being a woman, our age, our genes - but what this study does reaffirm is the notion that there are a number of risk factors that we can do something about. Drinking less alcohol, losing weight and reducing our use of synthetic oestrogens can all help to reduce risk. With this knowledge we may be able to reduce breast cancer rates now and in the future. Breast Cancer UK will continue to support research into identifying what causes breast cancer and how we can prevent it.
1. Brown, K. F. et al. (2018). The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. British Journal of Cancer 2018 Mar 23. doi: 10.1038/s41416-018-0029-6. [Epub ahead of print]
2. Parkin, D. M. (2011). Cancers attributable to inadequate physical exercise in the UK in 2010. British Journal of Cancer 105: S38-S41.
3. Wu, Y. et al. (2013). Physical activity and risk of breast cancer: a meta-analysis of prospective studies. Breast Cancer Research and Treatment 137(3): 869-888
4. Pizot, C. et al. (2016). Physical activity, hormone replacement therapy and breast cancer risk: A meta-analysis of prospective studies. European Journal of Cancer 52: 138-154.
5. Gonçalves, A. K. et al. (2014). Effects of Physical Activity on Breast Cancer Prevention: A Systematic Review. Journal of Physical Activity and Health 11: 445-454.
6. Theriau, C. F. et al. (2016). Voluntary physical activity abolishes the proliferative tumor growth microenvironment created by adipose tissue in animals fed a high fat diet. Journal of Applied Physiology 121: 139–153.
7. Schmidt, S. et al (2015). The integrative role of leptin, oestrogen and the insulin family in obesity-associated breast cancer: potential effects of exercise. Obesity reviews 16: 473–487.
8. McTiernan A. (2008). Mechanisms linking physical activity with cancer. Nature Reviews Cancer 8(3): 205–211.
9. Travis, R. C. et al. (2016). Night Shift Work and Breast Cancer Incidence: Three Prospective Studies and Meta-analysis of Published Studies. Journal of the National Cancer Institute 108(12): djw169.
10. Yuan, X. et al. (2018). Night Shift Work Increases the Risks of Multiple Primary Cancers in Women: A Systematic Review and Meta-analysis of 61 Articles. Cancer Epidemiology, Biomarkers and Prevention; 27(1): 25–40.