Calcium gives black teens heart benefits.

African Americans face more than twice the risk that whites do of developing high blood pressure, a major risk factor for atherosclerosis. This hypertension, which also tends to develop earlier in blacks, underlies a stroke rate that is 80 percent higher than that of the general U.S. population and a 50 percent higher mortality rate from heart disease. A new study indicates that among healthy black teenagers, consuming adequate calcium can help hold blood pressure down.

"When you have a problem as prevalent as hypertension [in blacks] and find an agent that can reduce that problem early in life, it may end up having enormous public health consequences," observes study leader James H. Dwyer, an epidemiologist at the University of Southern California School of Medicine, Los Angeles.

In the early 1980s, several studies found increased hypertension in persons with diets low in dairy products. Although such foods are rich sources of calcium, they also contain many other minerals that might be protective, complicating the interpretation of the results. In the new study, Dwyer's team isolated calcium's potential role in young blacks by giving supplements of the mineral to 65 girls and 51 boys.

For 8 weeks, on school days a high school nurse administered to each participant either a 1.5-gram calcium supplement or a look-alike tablet containing no nutrients. Most agreed to switch to the opposite type of tablet for a second, 8-week period. Twenty switched yet again, back to the first tablet, for a third phase of the study. Every 2 weeks, the researchers took the blood pressure of those who were still participating in the trial.

On average, diastolic pressure fell by 2 millimeters of mercury (mmHg) during periods when the teens received the extra calcium. The diastolic pressure is the vascular system's low point, occurring when the heart's chambers are filling with blood. The greatest drop--almost 5 mmHg--occurred among teens reporting diets low in calcium, Dwyer's team says in the September AMERICAN JOURNAL OF CLINICAL NUTRITION.

Systolic pressure, the system's maximum, occurs as the heart contracts and pumps blood. Calcium pills had no effect on this pressure--except perhaps in the teens whose diets were low in calcium.

Though blood pressure was within the healthy range in all of the students, Dwyer notes that without the calcium supplement "they tended to be in the top half of the normal distribution." The 5-mmHg drop in diastolic pressure seen in the low-calcium group, therefore, "would be sufficient to bring a large proportion of them below the average," he says. In fact, he notes, this diastolic-pressure drop is roughly equivalent to what has been observed in some adults who follow a low-fat, heart-healthy diet or who take blood-pressure medicine.

The finding that calcium supplements confer the greatest blood-pressure benefit on those with the lowest dietary calcium intake is consistent with what's been seen in adults, observes Janice Lea of the Emory University School of Medicine in Atlanta. Moreover, she notes, because heart disease can begin in youth, the new findings reinforce that "it's important to target young people and educate them about appropriate diets."

Though this new study hints that many black children might benefit from calcium supplementation, "we'd need a lot more studies to know for sure," maintains Elijah Saunders of the University of Maryland School of Medicine at Baltimore. Indeed, he says, compared to many other hypertension risk factors, such as excessive sensitivity to dietary salt (SN: 5/3/86, p. 280), stress, eating too little potassium, or obesity, "I don't think that calcium is a major player."

However, he adds, "this new study is interesting," and its findings deserve further investigation.