The following abstract was presented at the San Antonio breast Cancer symposium.

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Progesterone in Dairy Products Poses Risks: Presented at SABCS
By John Gever

SAN ANTONIO, TX -- December 14, 2007 -- Physicians may want to advise patients who are at high risk for breast cancer and other progesterone-sensitive conditions to avoid ice cream, butter, and other fatty dairy products, based on a study presented here at the 30th Annual San Antonio Breast Cancer Symposium (SABCS).

People absorb significant amounts of bovine progesterone (identical to human progesterone) from dairy products, thanks to the practice among dairy farmers of keeping dairy cattle pregnant most of the time, according to research led by William H. Goodson III, MD, Senior Clinical Research Scientist, California Pacific Medical Research Institute, San Francisco, California.

"Given the magnitude of milk use, we must consider the possibility that a single change in food production technology might have a major influence on the health of young persons who, with the best of intentions, are encouraged to drink milk," the report said.

Dr. Goodson presented the findings in a poster session on December 14. His group measured salivary progesterone levels in 17 male volunteers at baseline and 24 hours later after consuming three servings of high-fat dairy foods (2 tablespoons butter, 2 ounces cheese, and a quart of premium ice cream) between morning and afternoon. The procedure was repeated a week later.

Salivary progesterone levels were seen to spike by 30% to 100% in nearly all subjects after both sets of feedings.

Dr. Goodson said males were chosen because their normal concentrations of progesterone are lower and less cyclic than in females and hence an effect would be easier to measure.

"I'm more concerned about what happens in very young people, early in life when differences between males and females are less [significant]," Dr. Goodson said.

Dr. Goodson said most dairy cows began to be maintained in nearly constant pregnancy in the mid-20th century to maximize calf production. This results in increased progesterone levels in milk.

Unnoticed dietary progesterone might explain several medical trends identified in the latter half of the 20th century, including rising incidence of breast cancer and progressively earlier menarche in girls, Dr. Goodson's group suggested.

Because progesterone dissolves readily in fat, it should be absorbed more efficiently in high-fat products. Dr. Goodson said that plain milk, either skim or whole, is probably a less important source of dietary progesterone due to low concentration of fat (4% for whole milk). "It's the high-fat things that really get to you," he said.

The group measured progesterone levels in high-fat dairy products. Foods that were 70% to 80% dairy fat contained 175 to 300 ng/mL of progesterone, they found.

"The amount of progesterone in 200 mL of ice cream would be approximately one-one-hundredth of a pharmacological adult dose of 2 mg," according to the report.

Several previous studies have concluded that dairy consumption is unrelated to breast cancer incidence, according to Dr. Goodson and colleagues. But they also pointed to a more detailed study that examined particular dairy products, which did find associations between breast cancer incidence and high-fat cheeses as well as milk consumed in adolescence.

Another study found that women who ate ice cream -- but not low-fat frozen yogurt -- were significantly more likely to become pregnant. Dr. Goodson said dietary progesterone in ice cream could have been responsible by serving as progesterone replacement in women who may have luteal insufficiency, a form of infertility marked by low progesterone availability.

The implications of this hidden source of dietary progesterone are largely unexplored, Dr. Goodson said. "You could speculate a lot. It's an interesting place to begin speculating," he said.


[Presentation title: Milk Products Are a Source of Dietary Progesterone. Abstract 2028]