Effect of vitamin D supplementation during pregnancy on mid-to-late gestational blood pressure in a randomized controlled trial in Bangladesh

Abstract

Objective: To examine the dose-dependent effect of maternal vitamin D during pregnancy on blood pressure from mid-to-late gestation within the context of a randomized, placebo-controlled trial of vitamin D supplementation in Bangladesh (n = 1298).

Methods: Healthy women without hypertension were enrolled at 17-24 weeks gestation and randomized to one of four vitamin D doses during pregnancy: placebo, 4200, 16 800 or 28 000 IU/week. This substudy examined 1257 women with blood pressure measured at enrollment with at least one other timepoint (measurements included at 24 weeks, 30 weeks, and weekly from 36 weeks until delivery). Effects of vitamin D on SBP or DBP were analyzed using mixed-effects models.

Results: Vitamin D did not have an effect on SBP or DBP at 24 or 30 weeks; blood pressure was higher at 36 weeks for the highest dose versus placebo [mean difference (95% CI) mmHg: SBP = 2.3 (0.9-3.7); DBP = 1.9 (0.7-3.0)]. The differences in changes in SBP and DBP between vitamin D groups and placebo across intervals were small (P > 0.10), but the difference for 28 000 IU/week versus placebo was the highest from 30 to 36 weeks [SBP 0.2 (-0.1 to 0.5) and DBP 0.2 (-0.0 to 0.4) mmHg].

Conclusion: Vitamin D supplementation starting mid-pregnancy did not affect SBP or DBP until late gestation, and then only at the highest dose. These results do not support the clinical use of vitamin D in pregnancy to lower maternal blood pressure.

Trial registration: ClinicalTrials.gov NCT01924013.

FIGURE 1

SBP and DBP across treatment groups at enrollment (17–24 weeks gestation) Each box shows the interquartile range (25th to 75th percentile); the median depicted by the line in the middle of the box; upper and lower lines or whiskers show the adjacent values (1.5× interquartile range); outliers are shown as black circles. The mean (SD) SBP (mmHg) at enrollment by treatment group was: placebo, 98.3 (10.0); 4200 IU/week, 98.0 (8.8); 16 800 IU/week, 99.1 (9.6); 28 000 IU/week, 99.2 (9.3) and DBP was placebo, 62.0 (7.1); 4200 IU/week, 62.0 (7.1); 16 800 IU/week, 62.5 (7.4); and 28 000 IU/week, 62.0 (7.2). SD, standard deviation.

FIGURE 2

SBP and DBP across pregnancy by treatment group (placebo n = 250; 4200 IU n = 252; 16 800 IU n = 251; 28 000 IU n = 504). Lines represent predicted means estimated by mixed-effects models with cubic spline knots at 24, 30, and 36 weeks gestation (including all blood pressure values measured longitudinally from enrollment up to (but not including) the onset of labor) and interactions between treatment groups and gestational age spline terms.