U. ROCHESTER (US) — Low vitamin D levels may account for high blood pressure, which is more common and often more deadly in blacks than in whites.
Genetic factors common to blacks, including darker skin, reduce vitamin D synthesis—and a higher incidence of lactose intolerance among blacks, which can eliminate vitamin-D fortified milk from the diet, contributes further to lower dietary intake.
“Our study confirms that vitamin D represents one piece of the complex puzzle of race and blood pressure,” says Kevin Fiscella, professor of family medicine at the University of Rochester.
“And, since black-white differences in blood pressure represent thousands of excess deaths due to heart disease and stroke among blacks, we believe that simple interventions such as taking vitamin D supplements might have a positive impact on racial disparities.”
The research is reported in the Journal of General Internal Medicine.
An analysis of data from the National Health and Nutrition Examination Survey, 2001-2006 that included nearly 2,000 blacks and approximately 5,100 non-Hispanic whites, ages 20 and older, compared average systolic pressure and blood levels of vitamin D.
Most vitamin D is produced by the skin in response to sunlight and metabolized in the liver where it is converted to 25 hydroxyvitamin D or 25(OH) D, the form used to determine a person’s vitamin D status through a blood test. Deficiency is usually defined as less than 20 nanograms per milliliter; lower than 15 Ng/ml is inadequate to maintain bone health and normal calcium metabolism.
Fiscella’s data showed that 61 percent of blacks compared to 11 percent of whites have vitamin D levels in the lowest one-fifth of the population sample, whereas only 2 percent of blacks compared to 25 percent of whites had D levels in the highest group.
Fiscella notes some limitations to the study, and says vitamin D do not fully explain the racial differences in blood pressure.
“It is likely that other factors beyond vitamin D, such as psychological stress, medication adherence, and discrimination could contribute to this disparity,” he says.
“Further study using more refined measures of skin color is needed to tease apart the complex relationship between skin type, stress, vitamin D, and hypertension.”
The National Heart Lung and Blood Institute funded the research.
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