Milk is good for you, right? In general, it is. Sure, you can overdo it: 6 servings a day of whole milk has 900 calories, 48 grams of fat and 1,800 milligrams of calcium. Depending on the rest of your diet, that might be too much of a good thing.
But, in general, moderate intake of low-fat or skim milk is an excellent drink choice, especially if it is replacing highly sweetened drinks, like soda, that have little nutritional value.
There may be other "risks" associated with milk intake. There is a possible increased risk of prostate cancer among milk drinkers.
The notion that milk intake is linked to prostate cancer comes from studies that look at the diets of men with prostate cancer and compare them to the diets of similar men who don't have prostate cancer. Some of these studies have concluded that the risk of prostate cancer rises with increasing milk intake:
One review published in July 2009 by researchers in Brazil did not find a convincing link between prostate cancer risk and milk intake. But the researchers suggested that the issue deserved more study. They also found that milk intake might reduce the risk of type 2 diabetes and obesity.
One theory is that hormones in milk (including estrogen and "insulin like growth factor") might trigger prostate cancer or stimulate cancer cells to grow.
Another theory links cancer risk to milk's effects on vitamin D regulation. Milk is high in calcium. Past studies suggested that high calcium intake reduces conversion of vitamin D into its most potent form (1,25 dihydroxyvitamin D). This form of vitamin D may have a protective effect against cancer. With less of this form of the vitamin, cancer risk may increase. However, this remains an unproven theory. And, a study published in July 2009 found that calcium intake did not lower 1,25 dihydroxyvitamin D levels.
Given some evidence linking milk to prostate cancer, why do nutritionists consider milk and other dairy products part of a healthy diet?
There are several reasons:
In fact, most nutritionists do not warn of the dangers of milk because they don't believe the concern is needed.
If you are a man who likes to drink milk, I find no compelling scientific evidence to discourage you from doing so.
Then again, it's a good idea to keep an open mind. Future research could shed new light on the prostate cancer and milk connection. Whether we’re talking about milk or another dietary choice, we need studies to accurately estimate the risks of increasing intake as well as the risks of reducing it.
So, for now, consider milk a healthy food choice, as long as you stick with low-fat or nonfat versions and don't overdo it.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.