The Great Milk Debate: 9 Common Questions

At one time, milk was promoted as "the perfect food." Breast milk, of course, might be called the perfect food for an infant, but otherwise no one food is perfect or sufficient in itself. Still, milk and dairy products are very nutritious and the chief source of calcium in the American diet. They offer many benefits as part of a heart-healthy diet and are an essential component of the DASH diet, designed to control blood pressure. After decades of research, we know a great deal more now about milk. But legitimate questions, plus a number of myths, have multiplied.

The arguments about milk are highly politicized, with the dairy industry on one side and milk opponents on the other. Still, there is plenty of well-designed research, including some sponsored by the dairy industry and some from independent researchers. Here are answers to questions you may have.

Does drinking cow's milk cause cancer? Or protect against it?

I've heard both these claims. There's no clear link between milk and cancer--one way or the other. Dairy opponents say that milk increases the risk of breast, prostate, and ovarian cancer. A few studies support this idea, but other studies have not found any increased risk. In addition, milk may actually reduce the risk of colon cancer, because of its calcium and vitamin D. For example, a study in the British Journal of Nutrition in 2006 found that people who drank very little milk had a somewhat higher risk of colon cancer than those who drank at least a glass a day.

Should I avoid milk with rBST, the hormone some producers inject into dairy cows? I read this was a cause of early sexual development in girls.

Recombinant bovine somatotropin (rBST) is a growth hormone for cows, identical to the hormone they produce on their own. Cows injected with rBST produce more milk from the same amount of feed. This has ecological benefits: fewer cows making more milk saves feed, water, and farmland. It also might help reduce milk prices. But it makes cows more vulnerable to mastitis (an udder infection) and thus may require cows to be treated with antibiotics. There is no evidence that milk from cows injected with rBST is harmful to humans. Their milk is the same as any other milk--no chemical difference can be detected. All foods contain hormones naturally, and all milk contains BST. Still the public has been wary, and some producers now advertise that their milk comes from untreated cows and strongly imply it is safer. You can buy untreated milk if you wish, but there is no reason to fear rBST.

As for the early sexual development of girls, it is true that the age of menarche (onset of menstruation) has been gradually declining in the U.S. in the past century. In the mid-1990s (the latest data), menarche occurred a few months earlier (by as much as a year in some ethnic groups) than in the 1920s. No one knows what this means or why it is happening. But growth hormones in milk, in use only since the mid-1990s, are obviously not the cause. Better nutrition or the increasing levels of obesity among children may be at least partly responsible.

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