Effect of daily 2000 IU versus 800 IU vitamin D on blood pressure among adults age 60 years and older: a randomized clinical trial

Background: Observational studies report higher blood pressure (BP) among individuals with lower 25-hydroxyvitamin D concentration. Whether dosage of vitamin D supplementation has a differential effect on BP control remains unclear. Objective: The study aimed to determine if daily vitamin D supplementation with 2000 IU is more effective than 800 IU for BP control among older adults. Methods: This randomized, double-blind, ancillary trial of the Zurich Multiple Endpoint Vitamin D Trial in Knee Osteoarthritis enrolled adults aged >= 60 y who underwent elective surgery due to severe knee osteoarthritis. Participants were randomly assigned to receive high dose (2000 IU) or standard dose (800 IU) daily vitamin D-3 for 24 mo. Outcomes included daytime and 24-h mean systolic BP. BP variability and serum 25-hydroxyvitamin D concentration were examined in a post hoc and observational analysis. Results: Of the 273 participants randomly assigned, 250 participants completed a follow-up 24-h ambulatory BP monitoring (mean age: 70.4 +/- 6.4 y; 47.2% men). The difference in daytime mean systolic BP reduction between the 2000 IU (n = 123) and 800 IU (n = 127) groups was not statistically significant (-2.75 mm Hg vs. -3.94 mm Hg; difference: 1.18 mm Hg; 95% CI: -0.68, 3.05; P = 0.21), consistent with 24-h mean systolic BP. However, systolic BP variability was significantly reduced with 2000 IU (average real variability:-0.37mmHg) compared to 800 IU vitamin D3 (0.11mm Hg; difference: -0.48 mm Hg; 95% CI: -0.94, -0.01; P = 0.045). Independent of group allocation, maximal reductions in mean BP were observed at 28.7 ng/mL of achieved serum 25-hydroxyvitamin D concentrations. Conclusions: While daily 2000 IU and 800 IU vitamin D3 reduced mean systolic BP over 2 y to a small and similar extent, 2000 IU reduced mean systolic BP variability significantly more compared with 800 IU. However, without a placebo control group we cannot ascertain whether vitamin D supplementation effectively reduces BP. This trial was registered at www.clinicaltrials.gov as NCT00599807.