Does consumption of dairy and soy increase the risk of breast cancer?

A recent study conducted by researchers at Loma Linda University Health, investigated soy and dairy consumption in relation to risk of breast cancer. Entitled ‘Dairy, Soy, and Risk of Breast Cancer: Those Confounded Milks’, the study contained a cohort of 52,795 women in North America, initially free of cancer.

The findings of the study indicated that intakes of dairy calories and milk were associated with a slightly greater risk of breast cancer (independent of soy intake), whilst there was no association found between soy products and breast cancer. Fat levels of milk and consumption of yogurt and cheese showed no associations with breast cancer. A decreased risk of breast cancer was associated when substituting median intakes of soy milk for dairy milk, concluding that as milk intake increased so did the risk of breast cancer (when adjusted for soy intake).

Although the conclusions of the study were that the current guidelines for daily milk consumption could be viewed with some caution, its publication lead to the headline “One cup of milk a day associated with 50% increase in breast cancer risk.” This headline is misleading for a number of reasons. The study focuses purely on the relative risk as opposed to the absolute risk, and as the study was observational it didn’t establish the cause and effect. Dietary intake was also self-reported and only measured at baseline, which leaves room for errors. Furthermore, the study doesn’t take into account external contributors such as physical activity, smoking or alcohol – all of which could cofound the results. 

The results from this study also contradict with findings reported by The American Institute for Cancer Research which found no significant associations between dairy intake and breast cancer risk. This suggests that more research is needed to understand if there is a link between dairy intake and breast cancer.

Until further research is available, we continue to recommend eating dairy products in moderation (as per healthy eating guidelines) and to follow healthy lifestyle behaviours, which include a healthy dietary intake, regular physical activity and avoiding smoking.