High-Fat Dairy Foods Linked to Worse Survival After Breast Cancer

Connection may come from hormones found in animal fat, researcher suggests

By Kathleen Doheny
HealthDay Reporter

THURSDAY, March 14 (HealthDay News) -- Eating high-fat dairy products may raise the risk of death years later for breast cancer survivors, according to a new study that followed almost 1,900 women for up to nearly 15 years.

High-fat dairy includes foods such as whole milk, cream for coffee and butter. Low-fat dairy includes skim milk, nonfat milk, low-fat yogurt or nonfat yogurt.

Women "who ate one or more servings of high-fat dairy a day had a 49 percent higher risk of breast cancer death compared to those who ate up to half a serving a day," said study author Candyce Kroenke, a staff scientist with the Kaiser Permanente Division of Research in Oakland, Calif.

The women in the higher-intake group -- eating one serving or more a of high-fat dairy per day -- had a 64 percent higher risk of dying from any cause compared to those who consumed little or none, she added.

The link was much weaker for high-fat dairy and a recurrence of the breast cancer, she said, and was not strong enough to be significant statistically.

The study, supported by the U.S. National Cancer Institute, is published March 14 in the Journal of the National Cancer Institute.

Previous research by others, Kroenke said, has not found that a low-fat diet protects against dying from breast cancer.

She decided to explore high-fat dairy foods since they contain more estrogens -- which tend to reside in fat -- than do low-fat dairy foods. Breast cancers known as estrogen receptor-positive (ER-positive) are more common than ER-negative and require estrogen to grow.

The women in the new study were diagnosed with early breast cancer between 1997 and 2000. They were patients at Kaiser Permanente in California or were registered with the Utah Cancer Registry.

Women supplied information about their diet at the study start. Most also gave information on diet six years later.

In all, 349 women had a cancer recurrence over the follow-up period. Of the 372 women who died during that time, 189 deaths (about half) were due to breast cancer.

The researchers divided the women into three groups, from low to high intake of high-fat dairy foods.

The lowest group ate less than a daily half-serving (or none) of high-fat dairy. The highest group had a serving a day or more.

One limitation, Kroenke said, is the reliance on self-reported food records, subject to mistakes as no one remembers perfectly. So the link between high-fat dairy and death risk may be underestimated, she said.