Does calcium supplementation prevent hypertensive disorders in pregnancy?
High-dose calcium supplementation (i.e., at least 1,000 mg per day) during pregnancy reduces the risk of developing hypertension and preeclampsia. The most significant risk reduction occurs in women at risk of hypertensive disorders and those with low-calcium diets. (Strength of Recommendation: A, based on consistent, good-quality patient-oriented evidence.)
Hypertensive disorders occur in up to 10% of pregnancies and are a major source of fetal and maternal morbidity and mortality.1 Although early recognition and treatment have improved some outcomes, the pathogenesis of preeclampsia spectrum disorders is still not well understood. The incidence of all hypertensive disorders of pregnancy is increasing in the United States, making the need for prevention even greater. More than one-half of women of childbearing age do not have adequate calcium intake.2
The authors identified 13 randomized controlled trials (RCTs) comparing high-dose calcium supplementation (at least 1,000 mg per day) with placebo or no calcium in 15,730 women. Meta-analysis showed a risk reduction with calcium supplementation for hypertension (relative risk = 0.65; 95% confidence interval [CI], 0.53 to 0.81) and for preeclampsia (relative risk = 0.45; 95% CI, 0.31 to 0.65). Eight of the RCTs looked specifically at women with low-calcium diets (less than 900 mg per day). These trials included 10,678 women, and found even greater risk reduction for hypertensive disorders with calcium supplementation (relative risk = 0.36; 95% CI, 0.20 to 0.65). There was also a decrease in preterm births, but no difference in neonatal intensive care unit (NICU) admissions or stillbirths. Overall, the number needed to treat (NNT) to prevent one case of preeclampsia in the general population is 28, and in patients at high risk of preeclampsia, the NNT is 7.
The authors also examined 10 RCTs that evaluated low-dose calcium supplementation in 2,234 women. Although there were reductions in hypertension, preeclampsia, NICU admissions, and preterm birth, most of the participants were already at high risk of preeclampsia. Because of the high risk of bias and small sample size, more studies are needed to determine the effectiveness of recommending low-dose calcium supplementation.
In persons with low-calcium diets who are at high risk of hypertensive disorders, calcium supplementation could prevent the development of these disorders. Based in part on this Cochrane review, the World Health Organization recommends supplementing at-risk pregnant women with the equivalent of 1.5 to 2.0 g of elemental calcium daily (i.e., 3,750 to 5,000 mg of calcium carbonate daily).3 Family physicians should consider calcium supplementation in conjunction with other recommendations for preventing pregnancy-related hypertensive disorders.