Identifying healthful eating strategies such as increasing fruits and vegetables and limiting fatty foods appeals to consumers as a way to take control of their health. However, as these strategies are reported in science and medical journals, not all scientists are in agreement on the purported health benefits (or risk). In a study recently published in the American Journal of Clinical Nutrition, Harvard University researchers reported that dairy foods increase a man's risk of prostate cancer. But a careful analysis of this study casts some doubt on these findings.

The study included 20,000 men from the large, ongoing Physicians' Health Study and who were cancer-free at its start in 1984. Several times within the first 2 years they provided information regarding their diet and lifestyle, including how much cold breakfast cereal, skim milk, whole milk, cheese, and ice cream they typically ate. The researchers considered these five foods to be the main contributors to dairy intake. For the next 11 years, the investigators noted any new cases of prostate cancer.

When analyzed closely...

The researchers reported that those men who consumed 2½ servings of dairy foods each day had about a 30% greater risk of prostate cancer than those who consumed little or no dairy products (RR=1.34, 95% CI 1.04, 1.71). However, when the results were controlled for total energy intake - a potential factor in prostate cancer risk - the association did not reach significance (RR=1.27, 95% CI 0.97-1.66).

Why is milk suspected?

In recent years, there have been other claims linking dairy foods to prostate cancer. This hypothesis has been supported mainly by studies showing that countries (such as the United States) that consume large amounts of milk, cheese, and other dairy foods have a higher incidence of prostate cancer than those countries where few dairy products are consumed (such as Japan). But it's impossible to pinpoint dairy foods as a cause of prostate cancer based on this observation alone. For instance, the Japanese also eat more fish and soy products and less red meat and tend to be slimmer. All of these factors may decrease cancer risk.

The researchers present a mechanism by which calcium (abundant in dairy foods) suppresses vitamin D production, which may protect against prostate cancer. However, this has not been fully substantiated.

At this point, the best-documented risk factors for prostate cancer are age, race, and family history of the disease. One of the few modifiable risk factors that has been identified is dietary fat, especially saturated fat. Saturated fat is found mainly in animal products including dairy foods, but low-fat or fat-free milk and cheese contain very little or no fat at all.

Make healthful food choices

So, should men avoid dairy foods as a way to minimize their risk for cancer? Obviously, more research is needed to fully define the role of diet in the development of prostate cancer. Current recommendations from the United States' National Cancer Institute are to choose a diet with more fruits, vegetables and whole-grain breads and cereals, and smaller amounts of eggs, red meat, full-fat dairy (whole milk, butter, most cheeses), margarine and cooking oils. While full-fat dairy should be limited, the calcium in low-fat or fat-free milk, yogurt, and cheese helps maintain strong bones and may lower high blood pressure.