Vitamin D Therapy in Individuals with Pre-Hypertension or Hypertension: The DAYLIGHT Trial
Background—A large body of epidemiological and experimental evidence suggests that vitamin D deficiency may promote hypertension. This raises the possibility that vitamin D supplementation could be a simple intervention to reduce blood pressure, but data from prospective, randomized trials are limited.
Methods and Results—A double-blind, randomized controlled trial was conducted at 4 sites in the United States. We enrolled 534 individuals aged 18 to 50 years with low vitamin D status (25-hydroxyvitamin D levels ≤ 25 ng/ml) and systolic blood pressure 120-159 mm Hg. Participants were randomized to high-dose (4,000 IU/day) versus low-dose (400 IU/day) oral vitamin D3 for 6 months. The primary endpoint was change in mean 24-hour systolic blood pressure. Secondary endpoints included change in ambulatory diastolic blood pressure and clinic systolic and diastolic blood pressures. The median age was 38 years, and 62% of participants were men. Forty-six percent of participants were white, and 48% were black. The median 25-hydroxyvitamin D level at baseline was 15.3 ng/ml. Four-hundred fifty-five participants (85%) had at least one follow-up blood pressure measurement; 383 participants (72%) completed the full, 6-month study. At the end of the study, there was no significant difference in the primary endpoint (change in mean 24-hour systolic blood pressure, -0.8 mm Hg versus -1.6 mm Hg in the high-dose and low-dose arms, p=0.71) or in any of the secondary endpoints. Further, there was no evidence of association between change in 25-hydroxyvitamin D and change in 24-hour systolic blood pressure at 6 months (Spearman correlation coefficient, -0.05, p=0.34). Results were consistent across pre-specified subgroups.
Conclusions—Vitamin D supplementation did not reduce blood pressure in individuals with pre- or stage I hypertension and vitamin D deficiency. Our findings suggest that the association between vitamin D status and elevated blood pressure noted in observational studies is not causal.
Clinical Trial Registration Information—ClinicalTrials.gov. Identifier: NCT01240512.
- Received June 17, 2014.
- Revision received September 28, 2014.
- Accepted October 22, 2014.