Bold claim: Calcium supplements don’t prevent pre-eclampsia, even in pregnancies with low calcium intake. New findings from a refreshed Cochrane review challenge decades of assuming calcium helps avert hypertensive problems during pregnancy.
Researchers from Stellenbosch University analyzed large trials and found strong evidence that taking calcium during pregnancy does not reduce the risk of pre-eclampsia. Pre-eclampsia is a dangerous condition that typically emerges in the later stages of pregnancy, characterized by high blood pressure and organ dysfunction. In severe cases, the only solution is delivering the baby, which may require premature birth if the condition worsens.
Despite longstanding WHO guidance recommending daily calcium supplementation in populations with low calcium intake, this review casts doubt on its effectiveness and consistency of the supporting evidence. The researchers pooled data from ten randomized controlled trials including 37,504 participants, comparing calcium to placebo and high-dose to low-dose regimens. The overall conclusion was that calcium supplementation during pregnancy does not meaningfully prevent pre-eclampsia.
Even when comparing different doses, results remained largely unchanged. Mortality for mothers was rare across studies, while data on other critical outcomes like neonatal death and severe complications remained highly uncertain.
Anke Rohwer of Stellenbosch University emphasizes that applying rigorous and transparent methods revealed no meaningful differences in key outcomes such as pre-eclampsia, maternal death, preterm birth, or neonatal mortality. Older studies were often of questionable quality, making re-evaluation essential to ground current guidelines in solid evidence.
Earlier reviews included many smaller or less reliable studies that suggested a protective effect of calcium supplementation. When those studies were excluded due to reliability concerns or methodological flaws, the supposed benefits largely vanished. Publication bias and small-study effects likely inflated the impression of benefit in the past.
Professor Catherine Cluver, co-author, notes that the trustworthiness of primary research matters greatly. With problematic trials removed, the calcium-pre-eclampsia link loses its support from large, dependable trials. The study used the TRACT checklist to assess study trustworthiness, aligning with newer tools like INSPECT-SR designed to flag unreliable research.
Taken together, the updated analysis argues that calcium supplementation during pregnancy does not prevent pre-eclampsia, challenging a long-held preventive strategy—especially in settings where dietary calcium is limited. Clinicians and policymakers are urged to recognize how the evidence base has evolved and to adjust recommendations accordingly.
Source details:
Cluver, C. A., et al. (2025). Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database of Systematic Reviews. DOI: 10.1002/14651858.cd001059.pub6. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001059.pub6/full.
