What food we eat and how we eat it, and the relationship this has to cancer prevention or cause, remains confusing.

The latest piece of the puzzle regarding the role of dairy products and whether they decrease the risk of ovarian cancer was recently discussed in the American Journal of Epidemiology (Vol. 156: 148-57).

The researchers, led by Marc T. Goodman, PhD, MPH, from the University of Hawaii in Honolulu, and the Norris Comprehensive Cancer Center at the University of Southern California in Los Angeles, were concerned about the conflicting findings in several studies regarding the role of dairy products in reducing the risk of ovarian cancer.

To learn more, the researchers studied 558 women from three different ethnic groups: white, Asian (including Japanese, Chinese, Filipino or Korean descent), and "other" which included women who were from the Pacific Islands or Hispanic.

These women were diagnosed with ovarian cancer either in Los Angeles or Hawaii from 1993 to 1999. The researchers also included 607 women who did not have ovarian cancer, but were "matched" to the women with ovarian cancer according to a number of factors, such as age, where they lived, and their ethnic background.

The team did extensive in-person interviews in the women's homes to find out the types of food the women usually ate.

Like many studies before, this report found that there was a decrease in the risk of ovarian cancer for several factors not related to dairy products, including pregnancy, use of oral contraceptives, and tubal ligation (a surgical procedure to "tie" the fallopian tubes to prevent pregnancy.)

The role of dairy products in reducing the risk of ovarian cancer was not clear.

The authors reported that, for example, a woman's risk of ovarian cancer was decreased the more dairy products she consumed.

Yet, if you break out the different types of dairy products, the researchers found that some decreased the risk of ovarian cancer, while others did not. For example, low-fat milk decreased the risk of ovarian cancer, but whole milk did not. Butter also decreased the risk of ovarian cancer, but yogurt, cheese, and ice cream did not.

What could be the explanation for these differences?

The answer may be in some of the minerals or other substances found in certain dairy products and not in others.

In this study, both the amount of calcium and lactose women consumed in dairy products were related to the risk of ovarian cancer, with higher intake resulting in lower risk. Vitamin D, which is present in dairy products, did not decrease risk.

There is also the possibility, the authors noted, that there may be other unknown factors in certain dairy products that account for the decreased risk.

The report said that women who used oral contraceptives and had high calcium intakes had a "particularly low risk of ovarian cancer" with a risk reduction of 64%.

Although the information about calcium supplements was not as conclusive, there was a suggestion that oral calcium may reduce risk of ovarian cancer as well. But the results were not as definite as they were for the dairy products mentioned before.

There are several possible explanations for these findings, according to the authors. Dairy products may affect various hormone levels that in turn could influence the development of ovarian and other cancers.

"Although these results are intriguing, we cannot rule out the possibility that both calcium and lactose are surrogates ("stand-ins") for another, unidentified component of dairy foods," explained the authors.

What should women do when it comes to all the various diet recommendations to prevent cancers, such as ovarian cancer?

The American Cancer Society's Cancer Facts & Figures 2002 suggests: "It is not presently clear how single nutrients, combinations of nutrients, overnutrition and energy imbalance, or the amount and distribution of body fat at particular stages of life affect one's risk of specific cancers.

"Until more is known about the specific components of diet that influence cancer risk, the best advice is to emphasize whole foods and the consumption of a mostly plant-based diet."