Calcium

Pregnancy

The NIH Office of Dietary Supplements (ODS) lists calcium RDAs during pregnancy of 1,000 mg/day for ages 19 to 50 and 1,300 mg/day for ages 14 to 18. MotherToBaby states that food, beverages, supplements, and vitamins contribute to total calcium intake. ODS lists pregnancy upper intake limits of 2,500 mg/day for ages 19 to 50 and 3,000 mg/day for ages 14 to 18. These are total daily intake limits, not supplement targets. WHO's 2018 guideline recommends 1,500 to 2,000 mg/day of calcium supplementation in pregnant women in populations with low dietary calcium intake. WHO's 6 Oct 2026 fact sheet still lists calcium supplementation in areas with low dietary calcium intake, and its 2026 guideline page says the evidence synthesis was completed and an update was in progress. The Cochrane 2025 review included 10 randomized trials with 37,504 participants. Compared with placebo, the main analysis found little to no difference in pre-eclampsia (RR 0.83, 95% CI 0.67 to 1.04; 6 trials, 15,364 women; low-certainty evidence); its large-trial sensitivity analysis was also consistent with little to no difference (RR 0.92, 95% CI 0.79 to 1.05; 4 trials, 14,730 women; high-certainty evidence). Allotey et al. (2026) screened 46 potentially eligible trials with 33,516 women; 7 trials shared individual participant data. The IPD meta-analysis found no clear evidence of an overall reduction in pre-eclampsia (OR 0.89, 95% CI 0.73 to 1.07; 5 trials, 14,763 women) and estimated OR 0.65 (95% CI 0.48 to 0.90) when supplementation started at 10 weeks. Cochrane 2024 reviewed calcium supplementation for outcomes other than prevention or treatment of hypertension. It included 19 trials with 17,370 women and found a probable small reduction in preterm birth before 37 weeks (RR 0.80; 11 trials, 15,379 women; moderate-certainty evidence) and little or no effect on low birth weight (RR 0.93; 6 trials, 14,162 women; low-certainty evidence). The 2024 review does not establish effects of excessive antacid use. MotherToBaby reports a few neonatal seizure case reports after high-dose calcium carbonate near the end of pregnancy. Borkenhagen et al. (2013) reported one term newborn with hypocalcemic seizures after maternal intake of 3 to 6 g/day calcium carbonate during the final four months. Thornton et al. (2013) described another neonatal case after extremely high third-trimester calcium carbonate intake. These are case reports, not estimates of risk at ordinary total intake.

Breastfeeding

MotherToBaby says calcium is present in breast milk and calcium carbonate within recommended amounts is unlikely to harm a nursing baby. NHS Specialist Pharmacy Service (SPS) says calcium carbonate can be used at recommended doses for heartburn or indigestion while breastfeeding and that specific infant monitoring is usually not required. SPS also says there is no published evidence of use during breastfeeding, and its rationale includes calcium's natural presence in breast milk and calcium carbonate's poor oral absorption. These sources discuss calcium carbonate antacid use, not all calcium supplement forms. Direct milk-level and infant follow-up evidence was not identified in the cited guidance.

What was tested

The Cochrane 2024 review evaluated routine calcium supplementation for pregnancy and infant outcomes other than preventing or treating hypertension. Cochrane 2025 separately assessed calcium supplementation for hypertensive disorders and related outcomes, using prospective registration and trial trustworthiness criteria. Allotey et al. (2026) combined individual participant data from seven trials and aggregate data from other eligible trials. These reviews studied calcium supplements, not specific brands or a head-to-head comparison of carbonate and citrate. The neonatal seizure reports concern individual cases after very high calcium carbonate intake near term. The breastfeeding guidance concerns antacid-dose calcium carbonate; it does not report a direct milk-level or infant follow-up study.