Middle-aged adults who favor skim milk and other low-fat dairy foods may have lower blood pressure than others their age, a new study suggests.

Researchers in Spain found that among nearly 5,900 adults they followed over two years, those with the highest intake of low-fat dairy products were about half as likely to develop high blood pressure as those who consumed the fewest.

The apparent protective effect remained when the researchers accounted for other factors in high blood pressure risk - including overall diet, exercise, body weight and smoking.

Fattier dairy foods like whole milk and ice cream, however, were not a blood pressure boon, according to findings published in the American Journal of Clinical Nutrition.

Though some past research has linked low-fat dairy consumption to lower blood pressure, this is the first to find the relationship among middle-aged adults. Previous studies have focused on children and young adults, Dr. Alvaro Alonso, the lead author of the new study, told Reuters Health.

The findings from these studies do not prove that low-fat dairy foods have a direct benefit on blood pressure, noted Alonso, who is currently with the Harvard School of Public Health in Boston. But he said it at least seems that people who want to prevent high blood pressure can include low-fat dairy foods in their diets.

It’s not completely clear why dairy foods might help control blood pressure, but it does not appear to be due to calcium alone. In the current study, only calcium from low-fat dairy products was related to lower blood pressure risk, and past research has failed to find a clear association between higher calcium intake and lower blood pressure, Alonso said.

The study included 5,880 adults who ranged in age from 20 to 90 and were free from high blood pressure and cardiovascular disease at the start of the study. Participants completed questionnaires on their diets and other health and lifestyle factors, and the researchers followed up with them two years later to see how many had developed high blood pressure.

Overall, 180 people developed the condition during the study period. Those who had reported the highest intake of low-fat dairy - mostly in the form of skim and reduced-fat milk - were 54 percent less likely to develop high blood pressure than those with the lowest intakes.

Milk, the study authors note, provides certain proteins - caseins and whey proteins - that may act in a manner similar to blood-pressure-lowering drugs called angiotensin converting enzyme, or ACE, inhibitors. These proteins may help explain the study results, they speculate.

As for why only low-fat dairy had positive effects, it’s “plausible,” according to the researchers, that the saturated fat in richer dairy foods neutralizes any blood pressure benefits.

SOURCE: American Journal of Clinical Nutrition, November 2005.