The study, which is due to be published in the October issue of the Journal of Clinical Endocrinology & Metabolism, found that 2,000 IU of vitamin D per day could help decrease arterial stiffness by optimizing vitamin D status.
"While we think of the sun as providing humans with most of our body's requirements of vitamin D, 95 percent of the 44 black teenagers living in sunny Georgia who took part in this study were classified as vitamin D deficient," said Yanbin Dong, MD, PhD, of the Medical College of Georgia in Augusta and lead author of the study.
"Our study shows that vitamin D supplementation may improve cardiovascular health in black teens who don't get enough vitamin D from their diet and sun exposure."
The current recommended dietary adequate intake (AI) of vitamin D is 200 IU/day, but in October 2008 the American Academy of Pediatrics increased their recommendation for vitamin D intake for children and adolescents to 400 IU/day.
The authors highlight findings from previous research, which suggest that 1,000 to 2,000 IU is necessary to meet the body’s needs of vitamin D for most people.
Their study aimed to test whether 2,000 IU was an effective dose to improve vitamin D status in black teenagers, and to determine whether this would have any heart benefits.
The study recruited 44 black teenagers aged 15 to 18 who were randomly assigned to receive either 400 IU of vitamin D per day (control group) or 2,000 IU of vitamin D per day for 16 weeks.
Tests conducted at baseline, 4, 6 and 16 weeks included urine, height, weight, BMI, and fasting blood. Total body scans and blood pressure measurements were also conducted at the start and end of the trial.
The researchers also measured arterial stiffness using pulse wave velocity (PWV), a non-invasive procedure where a pulse is emitted at two arterial sites. The pulse's transit time and distance travelled is said to help researchers reliably calculate arterial stiffness.
Vitamin D status was also measured, with deficiency classified as 25(OH)D ≤50 nmol/L, and vitamin D sufficiency as 25(OH)D ≥75 nmol/L, and insufficiency as >50 to <75 nmol/L.
The researchers reported that those participants taking 400 IU of vitamin D per day did not achieve vitamin D sufficiency, while those who took 2,000 IU of vitamin D per day on average became vitamin D sufficient.
In addition, carotid-femoral PWV increased from baseline (5.38±0.53 m/s) to posttest (5.71±0.75 m/s) in the control group, whereas in the experimental group carotid-femoral PWV decreased from baseline (5.41±0.73 m/s) to posttest (5.33±0.79 m/s) (p=0.031).
“Our data suggest that supplementation of vitamin D could offer a means to elicit favorable functional alterations in the arterial system and in cardiovascular function in general,” said the researchers, but they highlighted that their data may be limited by the single-blinded study design.
“The present study indicates that the current AI of vitamin D should be revised upward in black youth. Of importance, atherosclerosis begins in youth, and therefore primary prevention of atherosclerosis should begin in adolescence,” they concluded.
A 16-week randomized clinical trial of 2,000 IU daily vitamin D3 1 supplementation in black youth: 25-hydroxyvitamin D, adiposity, and arterial stiffness
Journal of Clinical Endocrinology & Metabolism, to be published October 2010