Study Looks at Effect of Vitamin D Deficiency on Treatment for Hypertension

About one- third of US adults are deficient in vitamin D. Studies have shown a strong association between vitamin D deficiency and hypertension risk, as well as an inverse association between vitamin D levels and blood pressure. However, the effect of vitamin D supplementation on blood pressure management has not been closely studied.

At the 2013 American Heart Association Scientific Sessions, Thomas J. Wang, MD, director of the Division of Cardiovascular Medicine at Vanderbilt University Medical Center, and Physician-in-Chief at Vanderbilt Heart & Vascular Institute, presented results from the DAYLIGHT study that looked at whether “vitamin D supplementation would decrease blood pressure in individuals with both vitamin D deficiency and elevated blood pressure.”

For the study, researchers enrolled 534 patients who had 25-OH vitamin D levels ≤ 25 ng/ml, and who had been diagnosed with either pre-hypertension or stage 1 hypertension. Participants were randomized to receive either low-dose (400 IU/day) or high-dose (4000 IU/day) oral vitamin D3 for six months.

Also discussing the study results was cardiologist Keith C. Ferdinand, MD, professor of clinical medicine at Tulane University School of Medicine and chair of the National Forum for Heart Disease and Stroke. He noted that patients with a history of renal, liver, or cardiovascular disease, use of vitamin D supplements, or use of anti-hypertensive therapy were excluded from participating in the study.

He said the study population was 68% men and 32% women, the average age of participants was 39 years (participants’ age range was 18-50 years), and their systolic blood pressure ranged from 120-160 mm Hg (from normal to stage 2 hypertension, according to AHA categories). About half of the trial participants were overweight, and about half of participants were Afrinca-American. The six-month trial was done during winter months when there is less sunlight.

The primary endpoint of the study was mean 24-hour ambulatory systolic blood pressure. Secondary endpoints included 24-hour ambulatory diastolic blood pressure, daytime and nighttime ambulatory blood pressure, and clinic blood pressure.

According to the study write-up, the authors estimate that, after accounting for drop-outs, they “will have 80% power to detect a 2.8 mm Hg difference in the change in a 24-hour mean systolic blood pressure.”

The authors wrote in their conclusion that the DAYLIGHT study “is the first adequately powered, prospective, randomized trial of vitamin supplementation for elevated blood pressure. Because vitamin D deficiency is common and easy to treat, positive results could suggest a simple and cost-effective option for preventing or treating hypertension in the general population.”