A new study that suggests drinking dairy milk increases the risk of breast cancer is making headlines, but before you skip the milk in your smoothie, AICR experts say to consider the overall research. AICR’s latest breast cancer report, the most comprehensive analysis of the global evidence, found no evidence linking dairy or dairy milk to breast cancer risk.
This latest study adds to the body of evidence and will become part of AICR/WCRF’s Continuous Update Project, an ongoing program that analyzes the research from around the world. It was funded by AICR’s affiliate organization in the United Kingdom: World Cancer Research Fund.
The study was published in the International Journal of Epidemiology.
Dairy, soy and study findings
The study included close to 53,000 women from the United States and Canada who are part of The Adventist Health Study. Seventh-day Adventists often follow unique dietary habits. In this group, close to 40 percent were either vegetarians or ate no animal foods, including milk and eggs. Instead, soy is a common protein source. Only about half of the participants consumed similar amounts of dairy as other women living in America.
When the women joined the study, they filled out questionnaires asking about their soy, dairy and other eating patterns, along with lifestyle habits and cancer risk factors. All the women were free of cancer at the start of the study.
After almost eight years, 1,057 women in the study had developed breast cancer.
There were no associations found between soy consumption and breast cancer, independently of dairy intake. There were also no clear links to breast cancer found with cheese and yogurt.
When comparing the women who consumed the lowest to the highest amounts, however, this study found higher intake of dairy calories and milk linked to increased breast cancer risk. This was after adjusting for relevant risk factors, such as family history, BMI and alcohol intake. The link was clearest with milk calorie intake, with a 50 percent increased risk of women among the top 10 percent of milk drinkers compared to those among the bottom 10 percent. Risk was similar for both full-fat and low-fat versions and pre-menopausal and post-menopausal cases.
In this study, increasing amounts of milk intake linked to increasing risk. Calculations that replaced dairy milk with soy milk showed a lower risk of breast cancer.
Dairy and cancer, in context
There may be factors unaccounted for that play a role in the increased risk, the authors note, and diet was measured only once when the women joined the study. These limitations are common in this type of study, and is why it is important to analyze a body of research.
“It’s important to note this is just one study looking at women at the extreme ends of the consumption spectrum — the top 10 percent versus bottom 10 percent — in a very specific population,” said AICR Vice President of Research Nigel Brockton. “For the best estimate of the risk of breast cancer associated with milk consumption, take a look at the American Institute for Cancer Research/World Cancer Research Fund analyses, which show no increased risk with higher milk consumption.”
The AICR/WCRF breast cancer report actually found limited evidence that dairy lowered the risk of pre-menopausal breast cancer. This evidence is only suggestive; more research is needed.
Among other cancers, AICR research found strong evidence that dairy decreases the risk of colorectal cancer. Because some evidence — not as strong — points to dairy products increasing the risk of prostate cancer, AICR does not have a specific recommendation for dairy intake and cancer prevention.
The US dietary guidelines recommend women consume 3 cups of dairy daily. The dairy group includes calcium-fortified soymilk, along with milk, cheese, cottage cheese and yogurt. Technically, it’s not 3 cups of dairy foods; it is what counts as a cup and that differs depending upon the food. For milk and yogurt, one cup of each counts as one cup. But to get that one cup equivalent for cheddar and other hard cheese you will need 1.5 ounces and for cottage cheese you will need two cups. You can find a more complete list of cup equivalents from the USDA here.
“Dairy is packed with nutrition,” said AICR’s Director of Nutrition Programs Sheena P. Swanner, MS, RDN, LD. “It is a good source of calcium, which is important for building bones and teeth along with helping to maintain bone density, and a good source of protein which helps to build/repair muscle. Dairy foods also contain essential vitamins and minerals, such as potassium and phosphorous. Nearly all milk is fortified with vitamin D, which helps promote absorption of calcium.”
If you are unable or do not want to consume dairy products, find foods that provide the range of nutrients that dairy provides, the guidelines note.
“Focus on foods first — whenever possible. It’s important to get nutrients from food sources versus supplements,” adds Swanner. “For example, people may be surprised that there are many different foods that you can include in your diet to get calcium.” Foods that contain calcium include: greens (collards, broccoli, kale, bok choy), edamame, soybeans, tofu, dried figs, fortified drinks such as orange juice, nuts/seeds such as almonds and sesame seeds and calcium fortified cereals.
Reducing your risk
When it comes to lowering breast cancer risk, research shows there are clear steps women can take. The recent AICR/WCRF breast cancer report analyzed 119 studies, including data on 12 million women and 260,000 cases of breast cancer.
For older women, staying a healthy weight is one of the most important steps to take to minimize their risk – along with lowering risk of many other common cancers. Limiting or drinking no alcohol and being physically active also lower the risk of breast cancers. You can find out more about how lifestyle links to breast cancer risk in our Continuous Update Project report.
In addition to WCRF, the study was supported by the National Cancer Institute.