Doses of vitamin D more than six times the recommended daily limit can reduce arterial stiffness in blacks at risk for heart disease, a team of researchers at Augusta University in Georgia have found.

Arterial stiffness has long been an independent predictor of cardiovascular disease (CVD), first author Anas Raed, MD, and colleagues wrote in a PLOS ONE-published study, and evidence has suggested vitamin D deficiency could contribute to rigidity. Black patients in particular are at an increased risk for a deficiency, the authors wrote, since darker skin absorbs less sunlight and fat sequesters vitamin D.

Raed et al. studied 70 black patients between 13 and 45 years old—all of whom had arterial stiffness to some degree—for a period of four month. They found rapid, dose-response results in patients who consumed the most vitamin D.

Patients were administered a dose of either 4,000 international units of vitamin D, 2,000 IUs, 600 IUs or a placebo supplement. The recommended daily intake at the time was 600 IUs for most adults and children, according to the Institute of Medicine.

Using the American Heart Association-recommended gold standard for measuring arterial wall rigidity—pulse wave velocity—Raed and co-authors measured stiffness at four points during the study. Participants were administered monthly doses, rather than taking a pill at home, to ensure consistency.

Those who were on a regimen of 4,000 IUs of vitamin D saw the most positive results the quickest, the authors wrote, with a reduction in rigidity of 10.4 percent in just 16 weeks. The next tier of patients, who took in 2,000 IUs a month, saw a 2 percent decrease, while the placebo group experienced a 2.3 percent increase in stiffness.

The trial, believed to be the first of its kind, prompted the Institute of Medicine to alter their upper recommended limit of vitamin D to 4,000 IUs per day for adolescents and adults; the previous limit was half that amount.

“We think maybe in the future, when you go to your physician, he or she might check your arterial stiffness as another indicator of how healthy you are,” Raed said in a release from Augusta University.