Calcium

Does calcium lower the risk of pre-eclampsia?

Updated 4 Nov 2026

Short answer

The newest evidence says little or not at all. A 2025 Cochrane review found little to no difference in pre-eclampsia in large trials (risk ratio 0.92, 14,730 women).[1] Older reviews found a much larger effect, driven by small trials.[2] The World Health Organization (WHO) recommends 1.5 to 2.0 g a day where calcium intake is low.[3]

What the newest review found

Pre-eclampsia is high blood pressure in pregnancy with protein in the urine or a low platelet count, usually after 20 weeks.[4]

The 2025 Cochrane review included 10 randomized trials with 37,504 people. It removed 20 trials used in earlier versions: 11 because the rules for inclusion changed and 9 because of doubts about their trustworthiness.[1] Its results for calcium against placebo:[1]

  • All trials. Risk ratio 0.83 in 6 trials with 15,364 women, or 9 fewer cases per 1,000. The result could be due to chance, and the certainty is low.[1]
  • Large trials only. Risk ratio 0.92 in 4 trials with 14,730 women. This means little to no difference, with high certainty.[1]
  • Preterm birth, large trials only. Risk ratio 0.97 in 4 trials with 14,429 women, again with high certainty.[1]

The calcium intake of the women before the trial and their risk of pre-eclampsia did not change these findings.[1]

Why older reviews showed more

The 2018 version of the review pooled 13 trials with 15,730 women and found a risk ratio of 0.45, or 55% lower risk. It rated this evidence as low quality and warned that small trials might have inflated the effect. In its largest trial, the drop was 8% and could be due to chance.[5]

A 2024 analysis looked at the same data by trial size. In the 3 largest trials, with 88% of the women, the risk ratio was 0.92. Adding the small trials moved it to 0.45.[2]

500 mg or 1,500 mg

Two trials, in India and Tanzania, each gave 11,000 women in a first pregnancy either 500 mg or 1,500 mg a day:[6]

  • India. Pre-eclampsia occurred in 3.0% with 500 mg and 3.6% with 1,500 mg.[6]
  • Tanzania. Pre-eclampsia occurred in 3.0% with 500 mg and 2.7% with 1,500 mg.[6]

The lower dose was not worse for pre-eclampsia in either trial. For preterm birth it was not worse in India, but this could not be shown in Tanzania.[6] These trials had no placebo group, so they do not show whether either dose works better than no calcium.[6]

A trial in 1,355 women that started 500 mg a day before conception made no difference to the risk.[4]

What official bodies say

WHO recommends 1.5 to 2.0 g of calcium a day for pregnant women in populations with low calcium intake.[3] The American College of Obstetricians and Gynecologists states that 1,500 to 2,000 mg a day might reduce the severity of pre-eclampsia in women who get less than 600 mg a day.[4] These positions and the 2025 review do not agree, because the review found no change in its results by calcium intake.[1]

Other outcomes and safety

A 2024 Cochrane review found that calcium probably lowers preterm birth before 37 weeks (risk ratio 0.80), with little effect on low birth weight.[7] The large trials in the 2025 review did not confirm the preterm result.[1]

A 2022 review of 7 trials found no advantage for the bone density of mothers or children, even when dietary calcium was low. It called the overall effect on bone health unknown, because the results were inconclusive.[8] The 2018 Cochrane review saw more cases of HELLP syndrome, a pregnancy complication, with calcium (16 against 6). The authors called this increase small in absolute numbers.[5]

Who should be careful

The daily need in pregnancy is 1,000 mg in the US (1,300 mg at age 14 to 18), the same as for other women of the same age.[4] In the US, pre-eclampsia is a leading cause of serious illness and death in mothers and newborns. Anyone who is pregnant should ask a doctor or midwife before taking a high dose.[4]

Sources (8)

  1. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cluver CA, Rohwer C, Rohwer AC Cochrane Database Syst Rev, 2025. PMID 41330480
  2. Calcium supplementation for the prevention of pre-eclampsia: Challenging the evidence from meta-analyses. Wright D, Wright A, Magee LA, Von Dadelszen P, Nicolaides KH BJOG, 2024. PMID 38302677
  3. Calcium supplementation during pregnancy to reduce the risk of pre-eclampsia. World Health Organization, 2023. www.who.int
  4. Calcium: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  5. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Hofmeyr GJ, Lawrie TA, Atallah ÁN, Torloni MR Cochrane Database Syst Rev, 2018. PMID 30277579
  6. Two Randomized Trials of Low-Dose Calcium Supplementation in Pregnancy. Dwarkanath P, Muhihi A, Sudfeld CR, Wylie BJ, Wang M, Perumal N, et al. N Engl J Med, 2024. PMID 38197817
  7. Calcium supplementation (other than for preventing or treating hypertension) for improving pregnancy and infant outcomes. Kongwattanakul K, Duangkum C, Ngamjarus C, Lumbiganon P, Cuthbert A, Weeks J, et al. Cochrane Database Syst Rev, 2024. PMID 39560075
  8. Calcium supplementation during pregnancy and maternal and offspring bone health: a systematic review and meta-analysis. Tihtonen K, Korhonen P, Isojärvi J, Ojala R, Ashorn U, Ashorn P, et al. Ann N Y Acad Sci, 2022. PMID 34780069

More about calcium

What is calcium?Which foods contain calcium?Does calcium need vitamin D to work?How much calcium can the body absorb at one time?What is calcium used for?What happens if you do not get enough calcium?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.