March 18, 2013 | by Hiu Chung So
For women, dairy intake is often associated with building and maintaining strong bones, but its connection to breast cancer risk is more nuanced. Some research suggests that consumption of dairy foods is linked to a higher risk of the disease; other research suggests a preventive effect.
But what if it’s dairy foods' fat content that matters? That potential connection was explored in a March 14 article in the Journal of the National Cancer Institute based on a survey and follow-up of nearly 1,900 women diagnosed with breast cancer.
Because estrogenic hormones are found in fat, the authors hypothesized that higher-fat dairy products (made primarily by pregnant and nursing cows) would contain more of these compounds, thereby fueling breast cancer cells’ growth and recurrence.
For the study, the participants’ dietary habits were analyzed and divided according to how much high-fat and low-fat dairy products they consumed each day. The participants' were then tracked for breast cancer recurrence or mortality.
After almost 12 years, the researchers found that high-fat dairy consumption was linked to a higher likelihood of death. The group with the highest consumption (more than one serving a day) had a 64 percent greater risk of mortality than the group with the lowest consumption (less than half a serving a day).
Furthermore, this connection applied to deaths both from breast cancer and from other causes — with a 49 and 67 percent higher risk, respectively. However, there was no significant connection between increased high-fat dairy consumption and the risk of breast cancer recurrence.
The greater death risk was not seen in women who consumed high amounts of low-fat dairy.
Leslie Bernstein, Ph.D., professor and director of City of Hope's Division of Cancer Etiology, commented to HealthDay that this study yielded “an interesting finding” but that the results showed only a link, not a cause and effect.
“The women were not [randomly assigned] to getting different diets,” said Bernstein, who is not involved in the study.
The study also was limited in that it relied on self-reported surveys of the participants’ diet, and that other factors — including the cancer’s stage upon diagnosis and treatment methods used — might affect death risk, too.
Bernstein and the authors agreed that further study is needed but that, in the meantime, it wouldn’t hurt for women to shift to low-fat dairy.
Such a move could not only reduce estrogen exposure, it would reduce the amount of calories consumed. That could help keep weight gain and obesity — a known risk factor for breast cancer — in check.