Supplementation improved arterial stiffness in just 16 weeks in a small, randomised controlled trial (RCT) of vitamin D deficient obese/ overweight African-Americans.
Improvements were dose-dependent, with the highest vitamin D dose of 4000 international units/ day (IU/d) inducing a 10.4% reduction in arterial stiffness, discovered researchers from the Medical College of Georgia at Augusta University.
“Arterial stiffness was improved by vitamin D3 supplementation in a dose-response manner in overweight African Americans with vitamin D deficiency,” concluded first author Dr. Anas Raed.
"It significantly and rapidly reduced stiffness," Raed added.
Arterial stiffness is acknowledged as an independent risk factor for cardiovascular (CV) events and mortality. Recent research has identified an association between vitamin D deficiency and arterial stiffness.
A fixed dose of 2000 IU/d had demonstrated improved arterial stiffness in African-American adolescents in previous work conducted by Dr. Yanbin Dong, leader of this study.However, this is the first RCT to identify a dose-dependent benefit of vitamin D on the condition.
The RCT included 70 participants aged 13-45 years. Subjects were given either placebo, or the monthly equivalent of daily vitamin D3 doses of 600, 2000, or 4000 IU/d. (Medical staff administered the supplements monthly to ensure compliance).
All subjects were deficient at baseline with blood levels below the 50 nanomoles/ litre (nmol/l) (20 nanogrammes/ millilitre (ng/ml) threshold.
Arterial stiffness was measured by Pulse Wave Velocity (PWV) from the carotid artery of the neck to the femoral artery. PWV measures the speed of blood flow between two points. (The higher the speed, the greater the degree of arterial stiffness).
The 2000 IU/d group improved arterial stiffness by 2% in the 16-week supplementation period. The 600 IU/d group experienced a marginal stiffening of the arteries of 0.1%, while the placebo group showed a 2% increase in stiffness.
High-risk population group
The study population was chosen because previous research had revealed African-Americans to have higher rates of CV disease, lower vitamin D levels and greater arterial stiffness than their white counterparts.
Skin pigmentation is known to affect vitamin D skin absorption capability, with dark-skinned individuals having reduced capacity. Additionally, research has shown that vitamin D is stored in body fat compartments in obese or overweight people, and is therefore not released into circulation.
Vitamin D response
The dose of 4000 IU/d is over 6 times the usual dose of 600 IU/d recommended for adults and children by the U.S Institute of Medicine (IoM). The Food and Nutrition Board of the IoM regard this as the safe upper limit daily dose.
Unsurprisingly, the response in vitamin D blood concentration was highest in the 4000 IU/d group. At the end of the 16-week trial, blood levels in the high-dose group had risen to 89 nmol/l (35.7 ng/ml), and 76 nmol/l (30.5 ng/ml) in the 2000 IU/d group.
This finding suggests that for this particular population group and outcome, raising vitamin D level above the minimum threshold for sufficiency (generally regarded as 75 nmol/l (30 ng/ml)) may provide extra benefits.
Source: PLOS ONE
Volume 12, issue 12: e0188424, doi: 10.1371/journal.pone.0188424
“Dose responses of vitamin D3 supplementation on arterial stiffness in overweight African Americans with vitamin D deficiency: A placebo controlled randomized trial”
Authors: Anas Raed, Yanbin Dong et al