Why Dairy Foods May Not Increase Breast Cancer Risk

Dairy foods, such as cheese, yogurt, and milk, are good sources of calcium. And while calcium is thought to be protective against developing breast cancer, the overall links between dairy foods and breast cancer have been inconsistent.

An analysis published in the American Journal of Clinical Nutrition pooled the data from 21 previous studies to examine the associations between dairy products, calcium, and risk of breast cancer, including subtypes defined by estrogen receptor status. Here is what you need to know about dairy and breast cancer risk.

The Dairy Debate

There has long been debate about dairy foods and breast cancer risk. Some studies show that calcium, vitamin D, and a beneficial dairy fat called conjugated linoleic acid can regulate cancer cell proliferation and be protective against breast cancer.

However, dairy foods also potentially increase circulating insulin-like growth factor-1 (IGF-1) concentrations, which may promote cancer cell growth. And some worry that hormones in cows (both naturally occurring and administered in farming) may also increase breast cancer risk.

“Dairy is definitely one of the primary topics that comes up in relation to cancer and nutrition,” says Shauna Lindzon, a consulting dietitian in Toronto, Ontario, where she teaches nutrition at a cancer support center.

“Most people know that dairy provides essential nutrients such as calcium, but it is common for them to worry that dairy may have adverse effects,” says Lindzon. “Typical concerns include that dairy may be inflammatory or contain harmful hormones.”  

What the Research Says

The study referenced above pooled information from over 1 million women, who were followed for between eight and 20 years in 21 different cohort studies. Diet was assessed using food frequency questionnaires, which looked at the intake of milk, hard cheese ricotta/cottage cheese, yogurt, and ice cream.

The researchers looked at associations between calcium, dairy products, and the risk of developing invasive breast cancer overall, as well as the risk of developing breast cancer subtypes based on estrogen receptor status.

There are many different types of breast cancers, and some are sensitive to specific hormones in the body, including estrogen. Breast cancer cells have receptors that use hormones to fuel their growth. That means that any foods or medication that fuel their growth is problematic, and is why scientists are interested in how dairy hormones may play a role.

"This study of over 1 million women from 21 different cohorts found that dairy products, overall, are unlikely to increase breast cancer risk, and that fermented dairy products may lower risk, especially of harder to treat estrogen receptor-negative tumors," explains Marji McCullough, Senior Scientific Director, Epidemiology Research, at the American Cancer Society, and one of the researchers on the study.    

What You Need to Know

Concerns about dairy and breast cancer were largely put to rest. The researchers found null or very weak inverse associations between the dairy foods studied, calcium (from food or supplements), and the risk of developing overall or estrogen receptor (ER)-positive breast cancer. Further, the researchers found that certain dairy foods, such as yogurt, ricotta cheese, and cottage cheese are associated with a weak reduction in the risk of breast cancer.

"Consumption of small amounts of yogurt were associated with lower breast cancer risk, especially for harder to treat estrogen receptive-negative tumors," says McCullough. "Cottage/ricotta cheese consumption was associated with lower risk of ER-cancers only."

McCullough explains that the reasons for this are unclear, but may be due to probiotic content or some other unmeasured correlates of a healthy lifestyle.

But before you run out and buy ricotta or cottage cheese, note that the difference was only seen in studies outside of North America. That’s because of differences in food regulations, food processing, farming practices, and/or nutrient content, and that North American versions of these cheeses may have fewer beneficial probiotics.

“I am not surprised by the results in this study,” says Lindzon, who says that dairy is safe to eat for people with or without breast cancer, and notes that the new study aligns with advice from the American Institute for Cancer Research.

McCullough says that based on these findings, it appears unlikely that consuming dairy products or diets high in calcium would increase breast cancer risk. She adds "because dairy foods may lower the risk of some cancers but may increase risk of others, the American Cancer Society does not recommend dairy food consumption for cancer prevention."

A Word From Verywell

If you like dairy foods, know that they are likely safe to enjoy and are not associated with increased breast cancer risk. If you avoid dairy for any reason, make sure to get enough calcium from other sources.