Dairy and Cancer

Our patients with cancer commonly ask us about dairy – can they have it? Is it healthy? And what about dairy and cancer? For even the general public, the health benefits of dairy are difficult to determine as it could be beneficial or harmful depending on its variable effects as well as someone’s individual health history. For people with cancer, it becomes even more confusing as there is conflicting evidence on its helpfulness or harmfulness. This blog post is meant to provide you with some of the new evidence around dairy and cancer to help you make an informed decision about this food.

Nutritionally, dairy products are high in calcium and protein, as well as saturated fat. Historically, we thought that drinking milk and eating dairy was essential for getting adequate calcium and maintaining bone health however there is more to this story. Healthy bones need more than just calcium, and the daily dose of calcium that has been studied in growing children (around 600mg) can be easily achieved without dairy (see chart below). A variety of plant foods are also rich sources of calcium, in addition to other important vitamins, minerals, phytonutrients, and fibre. More and more, we are coming to realize that we have overemphasized dairy for bone health and underestimated its risks. Canada’s latest Food Guide has de-emphasized dairy, with lower fat dairy products comprising a smaller portion of the recommended protein foods and water being the recommended drink.

Many studies have examined the relationship between dairy consumption and cancer. While the evidence is mixed overall, there have been several studies reporting an increased risk with breast, prostate, ovarian and lung cancer and interestingly a lowered risk with colorectal cancer. The increased risk could be due to insulin-like growth factor (IGF-1) and other hormones found in milk that may contribute to the growth and development of some cancers. The evidence with colorectal cancer is more conflicting, with the reduction in risk relating specifically to the calcium content in milk. Calcium has been shown to bind to cancer-causing bile acids in the gut, helping to eliminate them.

A recent observational study suggests that increased consumption of dairy milk shows association with greater breast cancer risk. The authors found that consuming as little as 1/4 to 1/3 cup of milk per day was associated with a 30% increased risk of breast cancer. By drinking one cup per day, the associated risk went up to 50%, and for those drinking two to three cups per day, the risk increased further, to 70% to 80%. Furthermore, they 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%. There was no risk associated with yogurt or cheese intake in this study.

Dairy quality is important, especially when looking at how cows are raised. Conventional dairy is produced using factory-farming methods where cows are raised to produce as much milk as fast as possible. Regulations for factory farming allow cows to exist indoors in close proximity where they are under a great deal of stress and are fed unfamiliar corn and grains instead of grass and hay that they would primarily eat in the wild. While it is illegal to administer synthetic growth hormones to dairy cows in Canada (but not in the US), all milk contains naturally occurring growth hormones including IGF-1 and somatotropin, which may impact human health. Dairy produced in factory farm settings may also contain high levels of estrogen and progesterone as these cows are milked throughout their, often frequent, pregnancies. In comparison, organic, grass-fed and pasture-raised cattle often have tighter regulations, allowing them to roam more freely and consume more appropriate feed.

The bottom line is that milk is not a super-food and ideally, for those with breast, ovarian, lung and prostate cancer, is best minimized or avoided all together. For other people, organic and small operation-produced milk can be enjoyed occasionally. Fermented dairy products like kefir and yogurt may be superior to milk, as they contain beneficial probiotic bacteria.

Here is a list of comparable plant foods rich in calcium and protein, and low in saturated fat:

Author: Tehsina Jaffer, Naturopathic Intern at the CCNM Integrative Cancer Centre

References:

1. https://food-guide.canada.ca/en/healthy-eating-recommendations/make-it-a-habit-to-eat-vegetables-fruit-whole-grains-and-protein-foods/eat-protein-foods/

2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6466433/

3. https://academic.oup.com/ije/advance-article-abstract/doi/10.1093/ije/dyaa007/5743492?redirectedFrom=fulltext

4. https://www.sciencedirect.com/science/article/pii/S2352304214000373

5. http://www.downtoearth.ph/understanding-meat-terms-grass-fed-pastured-and-organic/