Calcium as antihypertensive agent?

If there were a critics' pick list for minerals, calcium might take this year's honors. On the heels of a report linking high calcium intake to a lowered colorectal cancer risk (SN: 12/7/85, p.362) come data showing that calcium can lower high blood pressure.

The report, which appears in the December ANNALS OF INTERNAL MEDICINE, is from David A. McCarron and Cynthia D. Morris of the Oregon Health Sciences University in Portland. The researchers previously stirred controversy with a finding that calcium, potassium and vitamins A and C were more important than salt in blood pressure control (SN: 6/30/84, p.404).

In the current study, McCarron and Morris looked at 48 people with high blood pressure and 32 people with normal blood pressure before and after eight weeks of taking 1 gram a day of elemental calcium--clightly more than the National Research Council's 800-milligram recommended dietary allowance.

In the hypertensive subjects, reclining systolic (contracting) blood pressure dropped 3.8 millimeters of mercury and diastolic (relaxation) pressure dropped 2.3 mm. The average blood pressure of the others remained essentially unchanged.

Epidemiologic research has shown that a drop of a few millimeters or so of mercury in blood pressure readings for the entire population would significantly reduce hypertension-related illness and death.

Some people responded better than others -- 44 percent of the hypertensives had drops of 10 mm or greater.

"We're dealing with a nutrient already being underconsumed in our society," McCarron says. While it would be foolhardy to pop massive doses of calcium, says McCarron, making sure one gets the recommended standard is a good idea.

But while McCarron saw "absolutely no side effects," an accompanying editorial by Hunter Heath III and C. Wayne Callaway of the Mayo Clinic in Rochester, Minn., expresses concern about possible constipation, nausea, bloating, interference with drug absorption, kidney stone formation and kidney damage associated with taking calcium tablets.

What remains to be seen is in whom, and why, the blood pressure effect occurs. The study, funded by the federal government, two private organizations and Miles Laboratories, Inc., of Elkhart, Ind., was large enough to pick up the blood pressure change, "but to get predictors we wold have needed a study 10 times the size," says McCarron.

Says Michael Horan, head of hypertension research at the National Heart, Lung, and Blood Institute in Bethesda, Md., "With high blood pressure afflicting nearly 58 million Americans, we're of necessity always interested in non-pharmacological approaches to the problem." While he hadn't yet seen the McCarron study, he told SCIENCE NEWS that "the trial sounds reasonable" and that evidence is beginning to accumulate that dietary calcium may play a role in the modulation of blood pressure.