Breast cancer researchers and nutritionists have struggled for years to answer a complex question: is dairy consumption related to breast cancer? Findings released today begin to chip away at the uncertainty. In women already diagnosed with breast cancer, consuming at least a half serving of high-fat dairy per day increased the risk of dying from the disease while low-fat dairy consumption had no effect.
The findings, which appear in the Journal of the National Cancer Institute, showed that high-fat dairy consumption also was linked with higher death rates from causes other than breast cancer in women enrolled in the study. However, the researchers did not find a significant association between high-fat dairy intake and breast cancer recurrence.
Women in the study were diagnosed with early-stage, primary breast cancer between 1997 and 2000, and they were treated with radiation, chemotherapy, and tamoxifen. Initially, 1893 women filled out comprehensive food frequency questionnaires; 1513 provided follow-up information 6 years later.
All women enrolled were asked about their intake of high-fat dairy products, including whole milk, cream, butter, cheese, ice cream, custard, and pudding. Their average age was about 58 years, and about 80% were white. About 75% were postmenopausal at diagnosis. During the median 12-year follow-up period, 349 women had a recurrence. Of 372 deaths, 189 women died of breast cancer.
“Specifically, women consuming 1 or more servings per day of high-fat dairy had a 64% higher risk of dying from any cause and a 49% increased risk of dying from their breast cancer during the follow-up period,” lead author Candyce Kroenke, ScD, MPH, of Kaiser Permanente in Oakland, Calif, said in a statement.
Kroenke and her colleagues also showed that women who ate and drank smaller amounts of high-fat dairy, one-half to 1 serving per day, had a 20% increased risk of dying of their breast cancer compared with women who ate less than half a serving per day.
The study found no link between overall dairy consumption and breast cancer recurrence or survival, the authors noted. They also found no link between calcium and vitamin D in dairy products and breast cancer outcomes. Kroenke and her colleagues suggested that estrogen, a known risk factor for breast cancer, is involved. Milk and products made from it in Western countries come primarily from pregnant cows, whose milk would contain higher levels of estrogen. Removing the fat from dairy products subsequently lowers the estrogen levels.