Randomized, placebo-controlled, calcium supplementation trial in pregnant Gambian women accustomed to a low calcium intake: effects on maternal blood pressure and infant growth

Abstract

Background: Dietary calcium intake in rural Gambian women is very low (∼350 mg/d) compared with international recommendations. Studies have suggested that calcium supplementation of women receiving low-calcium diets significantly reduces risk of pregnancy hypertension.

Objective: We tested the effects on blood pressure (BP) of calcium carbonate supplementation (1500 mg Ca/d) in pregnant, rural Gambian women.

Design: The study was a randomized, double-blind, parallel, placebo-controlled supplementation trial from 20 wk of gestation (P20) until delivery (calcium: n = 330; placebo; n = 332). BP and anthropometric measures were taken at P20 and then 4 weekly until 36 wk of gestation (P36), and infant anthropometric measures were taken at 2, 13, and 52 wk postdelivery.

Results: A total of 525 (calcium: n = 260; placebo: n = 265) women had BP measured at P36 and subsequently delivered a healthy term singleton infant. Mean compliance was 97%, and urinary calcium measures confirmed the group allocation. At P20, the mean (±SD) systolic blood pressure (SBP) was 101.2 ± 9.0 and 102.1 ± 9.3 mm Hg, and diastolic blood pressure (DBP) was 54.5 ± 7.3 and 55.8 ± 7.8 mm Hg, in the calcium and placebo groups, respectively. The intention-to-treat analysis that was adjusted for confounders showed no significant effect of calcium supplementation on the change between P20 and P36 (calcium compared with placebo; mean ± SEM) in SBP (-0.64 ± 0.65%; P = 0.3) or DBP (-0.22 ± 1.15%; P = 0.8). There was no significant effect of supplementation on BP, pregnancy weight gain, weight postpartum, or infant weight, length, and other measures of growth. However, the comparability of the original randomly assigned groups may have been compromised by the exclusion of 20.7% of women from the final analysis.

Conclusions: Calcium supplementation did not affect BP in pregnancy. This result may have been because the Gambian women were adapted to a low dietary calcium intake, and/or obesity, high gestational weight gain, high underlying BP, tobacco use, alcohol consumption, and sedentary lifestyles were rare. This trial was registered at the International Standard Randomized Controlled Trial Register (www.controlled-trials.com/mrct/) as ISRCTN96502494.

FIGURE 1.

Flowchart of recruitment, exclusions, and losses for the trial Calcium requirements of pregnant women in The Gambia (http://www.controlled-trials.com/mrct/; ISRCTN96502494). For participant data excluded from analysis because of misclassification or multiple pregnancy, misclassified refers to women who were more advanced in gestation at enrollment than diagnosed by the midwife and, therefore, delivered a term baby earlier than anticipated; multiple pregnancy refers to one not identified as such at recruitment by the midwife. This classification became apparent later during pregnancy or at delivery. BP, blood pressure.