Randomized, placebo-controlled, calcium supplementation trial in pregnant Gambian women accustomed to a low calcium intake: effects on maternal blood pressure and infant growth
What this study found
Calcium supplementation did not lower maternal blood pressure or improve infant growth. In the calcium group, the P20 to P36 change in blood pressure was not meaningfully different from placebo for systolic blood pressure, 20.64 6 0.65% (P = 0.3), or diastolic blood pressure, 20.22 6 1.15% (P = 0.8). Infant outcomes were also unchanged, with birth weight 2.9 6 0.4 kg (n = 171), birth length 485 6 24 mm (n = 171), and 52-week weight 7.9 6 1.1 kg (n = 243). The authors concluded that the lack of benefit may reflect adaptation to chronically low calcium intake and other lifestyle factors…
- Study & population
- Randomized, double-blind, placebo-controlled trial in pregnant women in rural West Kiang, The Gambia, with very low habitual calcium intake and uncomplicated singleton pregnancies.
- Intervention
- Pregnant women in the active arm received 1500 mg elemental calcium per day as 3 oral chewable calcium carbonate tablets (500 mg each) from about 18 to 22 weeks' gestation until delivery, with tablets taken daily in the evening; during Ramadan they were taken after fasting ended and before the main meal.
- Key limitation
- Substantial post-randomization loss reduced the calcium arm from 330 randomized women to 260 in the final analytic set, and infant measurements were available for smaller subsets.
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Open PDFOriginal 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.