Harvard researchers said that “dairy food is one of the most consistent predictors for prostate cancer in the published literature.” But it’s not just prostate cancer. Here’s a study that found a link between dairy food and lung, breast, and ovarian cancers:

Lactose Intolerance And Risk Of Lung, Breast And Ovarian Cancers: Aetiological Clues From A Population-Based Study In Sweden, British Journal of Cancer, January 2015

Conclusions: In this large cohort study, people with lactose intolerance, characterised by low consumption of milk and other dairy products, had decreased risks of lung, breast, and ovarian cancers, but the decreased risks were not found in their family members, suggesting that the protective effects against these cancers may be related to their specific dietary pattern.

Many studies rank dairy consumption from high to low and compare the highest group to the lowest group for cancer incidence. A drawback to that is relying on questionnaires, that is, relying on peoples’ memory and their inclination to tell the truth. Here we have a group of people who were, in effect, punished if they ate dairy (by their inability to digest milk sugar); researchers had more confidence that they were low consumers.

What is it about dairy food that could link it to cancer?

Milk and other dairy products can contain high amounts of fats, particularly saturated fat, and some growth factors, such as insulin-like growth factor I (IGF-I), and these dietary components have been suggested to be associated with the development of various types of cancers.

Furthermore, avoidance of milk may alter the human gut microbiome, which may affect the development of tumours.

I just posted a couple studies linking saturated fat to breast cancer.

My sense is that there are several components of dairy food that make it risky. It’s probably not just the fat, or the IGF-1, or the milk protein, or the galactose, or the environmental pollutants. It may be all of these acting together.