Milk and Breast Cancer.

By Dr. Ellen Conte (McDonell), ND.

A recent study found that milk consumption increased the risk of breast cancer.(1) Understandably, this may be worrisome for some women.

The observational study looked at food intake from a little over 50,000 women who did not have cancer, and followed them for almost 8-years. They found that women who consumed milk had a higher risk of breast cancer – about 50% higher for those who drank around 1 cup per day compared to those who drank none. There was no risk with yoghurt or cheese intake, which is reassuring. They also found that soy milk and other soy foods did not increase the risk of breast cancer, and that replacing cow’s milk with soy milk lowered the risk of breast cancer by about 30%.

So, what do we do with this?

The first important thing to note is that observational studies such as this cannot prove causation – meaning this study does not prove that milk causes breast cancer. Other studies have not found the same risk which is important to note.(2) Other studies have however found protective or neutral effects from soy, so the research is consistent for the lack of harm and often benefit of soy.(3)  At this time, the strongest statement we can make is that cow’s milk consumption may increase the risk of breast cancer, but more research is needed to know for sure.

While we’re waiting for more research to help clarify: given the uncertainty regarding the risk of cow’s milk and breast cancer, and the more consistent safe and potentially protective effects of soy, it seems a reasonable suggestion to reduce intake of cow’s milk and consider switching some or all of your cow’s milk to soy milk.  Other sources of dairy such as yoghurt and cheese can still be enjoyed and can help women to meet their protein and calcium-needs.  Dairy is not an essential part of a healthy diet, as indicated by Canada’s food guide, but dairy (particularly yoghurt and lower-fat cheeses) can certainly be part of a healthy diet if desired.  As always, discuss your health and nutrition with a healthcare provider to determine what is best for you.

Reference: Fraser GE, Jaceldo-Siegl K, Orlich M, Mashchak A, Sirirat R, Knutsen S. Dairy, soy, and risk of breast cancer: those confounded milks [published online ahead of print, 2020 Feb 25]. Int J Epidemiol. 2020;dyaa007. doi:10.1093/ije/dyaa007

References:

1.    Fraser GE, Jaceldo-Siegl K, Orlich M, Mashchak A, Sirirat R, Knutsen S. Dairy, soy, and risk of breast cancer: those confounded milks. Int J Epidemiol. 2020:dyaa007.
2.    Chen L, Li M, Li H. Milk and yogurt intake and breast cancer risk: A meta-analysis. Medicine. 2019;98(12):e14900-e14900.
3.    Chen M, Rao Y, Zheng Y, et al. Association between soy isoflavone intake and breast cancer risk for pre- and post-menopausal women: a meta-analysis of epidemiological studies. PloS one. 2014;9(2):e89288-e89288.