Recent studies have linked high blood pressure with low levels of vitamin D. Both black and white Americans are affected, but blacks are hit with a double whammy — significantly higher rates of high blood pressure and heart disease, and lower levels of vitamin D.

Do you need to lower your blood pressure? You may want to consider taking a vitamin D supplement. — Big Cheese Photo/Corbis

Could supplements treat and perhaps prevent high blood pressure in older African Americans?

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Past studies have shown inconsistent results, possibly because of an insufficient number of black participants. In a recent study, published in the April issue of the journal Hypertension, researchers randomly assigned 250 African American men and women, average age 51, to one of four groups for a three-month study of vitamin D supplements.

Participants took one daily capsule of either a placebo, 1,000 international units (IU) of vitamin D, 2,000 IU of vitamin D or 4,000 IU of vitamin D.

The Institute of Medicine considers 4,000 IU daily a safe upper limit for vitamin D supplementation. Neither the research staff nor the participants knew who was getting which capsule.

The study found that the more vitamin D participants took, the greater their drop in blood pressure. Those taking the maximum dose of 4,000 IU daily saw a 4-point drop in systolic blood pressure — the top number in blood pressure readings and the most important one for older adults — while the group taking the placebo had a 1.7-point increase in systolic pressure. Systolic pressure measures the force of the blood in the arteries as the heart beats.

"The gains were modest but significant," says John Forman, M.D., lead author and assistant professor of medicine at Brigham and Women's Hospital in Boston.

Clyde Yancy, M.D., chief of the division of cardiology at the Northwestern University School of Medicine in Chicago, who was not involved in the research, says, "The findings are curious and certainly pique our interest about the role that vitamin D deficiency plays in the development of cardiovascular disease, but at best it's a slight role. Supplementation seems to make some difference, but not much more than can be accomplished by a heart-healthy diet."

Nissa Simon is a freelance health writer and frequent contributor to AARP.

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