A new study adds to the growing evidence that calcium may help reduce high blood pressure in some people.

University of Wisconsin researchers, who actually were trying to study the effects of a certain kind of calcium supplement on women's bones, noticed that blood pressure went down in women who were already taking medication for high blood pressure.

Over the course of the study, average blood pressure went down 13 points in the women who took calcium, and up by seven points in those who didn't, says Nancy E. Johnson of the University of Wisconsin at Madison.

Calcium is present in milk, sardines, yogurt, broccoli and other foods, and also is available in supplement pills. The Wisconsin Milk Marketing Board Inc. was one of the sponsors of the research. Calcium is often recommended to prevent loss of bone mass (osteoporosis), and possible bone fracture, in women after menopause.

Why it seems to lower blood pressure is unclear, Johnson and several colleagues write in The American Journal of Clinical Nutrition. She says that doctors, who already urge high blood pressure patients to eat less sodium and more potassium, "should consider whether a patient might be calcium-sensitive."

Calcium did not lower the blood pressure of women who started the study with normal pressure, nor did it have any effect during exercise. Only resting blood pressure was affected.