Study: High Doses of Vitamin D Rapidly Reduce Arterial Stiffness

The mechanism of action is not fully understood, but additional trials are indicated

In just four months, high doses of vitamin D reduced arterial stiffness in young, overweight/obese, vitamin-deficient, but otherwise still healthy African-Americans, researchers say.

Rigid artery walls are an independent predictor of cardiovascular-related disease and death, and vitamin D deficiency appears to be a contributor, says Yanbin Dong, MD, PhD, geneticist and cardiologist at the Georgia Prevention Institute (GPI) at the Medical College of Georgia (MCG) at Augusta University.

So researchers looked at baseline and again 16 weeks later in 70 African-Americans 13 to 45 years of age—all of whom had some degree of arterial stiffness—taking varying doses of the vitamin best known for its role in bone health. In what appears to be the first randomized trial of its kind, they found that arterial stiffness was improved by vitamin D supplementation in a dose–response manner in this population, they wrote in the journal PLoS ONE.

Overweight/obese blacks are at increased risk for vitamin D deficiency because darker skin absorbs less sunlight—the skin makes vitamin D in response to sun exposure—and fat tends to sequester vitamin D for no apparent purpose, says Dong, the study's corresponding author.

Participants taking 4,000 international units (IU)—more than six times the daily 600 IU the Institute of Medicine currently recommends for most adults and children—received the most benefit, says Dr. Anas Raed, MD, research resident in the MCG Department of Medicine and the study's first author.

The dose, now considered the highest safe upper dose of the vitamin by the Institute of Medicine, reduced arterial stiffness the most and the fastest: 10.4% in four months. Stiffness was significantly and rapidly reduced, Raed says.

Two thousand IU decreased stiffness by 2% in that time frame. At 600 IU, arterial stiffness actually increased slightly (0.1%), and the placebo group experienced a 2.3% increase in arterial stiffness over the time frame.

The researchers used noninvasive, gold-standard pulse wave velocity to assess arterial stiffness. Reported measures were from the carotid artery in the neck to the femoral artery, a major blood vessel, which supplies the lower body with blood. The American Heart Association considers this the primary outcome measurement of arterial stiffness.

The varying doses, as well as the placebo participants took, were all packaged the same, so neither they or the investigators knew which dose, if any, people were getting until the study was complete. Both placebo and supplements were given once monthly—rather than daily at home—at the GPI to ensure consistent compliance.

While heart disease is the leading cause of death in the United States, according to the Centers for Disease Control and Prevention, African-Americans have higher rates of cardiovascular disease and death than whites and the disease tends to occur earlier in life. The authors write that arterial stiffness and vitamin D deficiency might be potential contributors.

Just how vitamin D is good for our arteries isn't completely understood, but it appears to impact blood vessel health in many ways. Laboratory studies have shown that mice missing a vitamin D receptor have higher activation of the renin-angiotensin-aldosterone system, Raed says. Activation of this system increases blood vessel constriction, which can contribute to arterial stiffness. Vitamin D can also suppress vascular smooth muscle cell proliferation, activation of garbage-eating macrophages, and calcification formation, all of which can thicken blood vessel walls and hinder flexibility. Vitamin D also reduces inflammation, an underlying mechanism for obesity-related development of coronary artery disease, Raed says.

Now it's time to do a larger-scale study, particularly in high-risk populations, and follow participants' progress for longer periods, Dong and Raed say. "A year would give us even more data and ideas," Raed adds.

Source: EurekAlert; January 2, 2018.