People who are diagnosed with breast cancer and then go on to consume a steady diet of high-fat dairy foods increase their chances of dying years earlier than those who consumed low- to nonfat milk products, according to a new study by Kaiser Permanente researchers.
The study, published Thursday in the Journal of the National Cancer Institute, is considered the first to look at the differences in high-fat and low-fat dairy intake following a breast cancer diagnosis on long-term survival.
The results don't suggest that people eliminate dairy from their diet entirely. "But it can't hurt to alter consumption of higher-fat milk to low-fat or non fat," said Candyce Kroenke, staff scientist with the Kaiser Permanente Division of Research in Oakland and lead author of the study.
For the study, researchers looked at the dietary habits of nearly 1,900 women, mostly Northern California Kaiser patients, who were diagnosed with relatively early-stage, invasive breast cancer between 1997 and 2000.
Those who consumed one or more servings per day of high-fat dairy products -- such as whole milk and cream, condensed or evaporated milk, ice cream and custards -- had a 49 percent increased risk of dying from breast cancer during the 12-year follow-up than those patients who limited their amount of high-fat products, the study found. They also had a 64 percent higher risk of dying from any cause during that period, most often from cardiovascular diseases.
The study's authors theorized estrogen levels are elevated in milk products produced in Western countries because dairy cows are often pregnant to maximize production, and pregnancy elevates their estrogen levels.
Most breast cancer tumors are sensitive to the estrogen hormone, meaning the estrogen causes the cancer to grow. Researchers believe that the higher the fat content of the milk product, the higher the concentration of estrogen.
"It raises concerns that the way we produce milk should lead people to consider alternatives, especially if they have an elevated risk of breast cancer or if they have breast cancer and are trying to alter their lifestyles," Kroenke said.
Officials from the Dairy Council of California agreed that switching from full-fat to low- or non fat milk products may be a healthful choice for some people, but they questioned and disagreed with the study's conclusions.
"They've showed an association basically between whole milk consumption and deaths from breast cancer. That is very, very far from proving one causes the other," said Lori Hoolihan , nutrition research specialist with the Dairy Council of California.
Hoolihan said the researchers could not have accounted for every lifestyle or environmental factor that could contribute to increased mortality from breast cancer or other causes. She also said the amount of estrogen found in a cup of milk is so much less than in the human that it could not pose a risk.
But she said the variety of milk products allows people to make choices. "You don't want to give them up altogether because you're missing out on a huge nutrient package," she said.
Dr. Susan Kutner, chairwoman of Kaiser Permanente Northern California's Breast Care Task Force, said more research is needed on the potential link between high-fat dairy and breast cancer. She said dietary studies are difficult to do because they rely on participants to report their food and drink consumption.
Still, Kutner, who was not involved in the research, considered the study to be scientifically rigorous and said she would use it in discussions with her patients.
Kaiser patient Denise Pangelinan did not participate in the study nor was she familiar with the research, but she cut back on dairy products almost immediately after her breast cancer diagnosis in October 2011.
"When I got sick, the only thing I could control at that point was my diet, my attitude and exercise," said Pangelinan, 47, who consulted with a nutritionist who specialized in cancer.
Everything she learned and read encouraged her to greatly reduce the amount of dairy and meat in her diet so the study's conclusions made sense, she said. She now eats more vegetables, often in the form of smoothies.
"It's not to say I don't treat myself to a bowl of Ben & Jerry's now and then," she said. "But having a lot more green veggies in my diet has just given me overall better health."