The March, 2006 issue of the American Journal of Obstetrics and Gynecology published the findings of a World Health Organization randomized trial that a daily calcium supplement helps prevent complications associated with preeclampsia among pregnant women whose intake of the mineral is low. Preeclampsia is a condition that can occur during pregnancy which is characterized by high blood pressure and protein in the urine, and can lead to life-threatening complications for both mother and child.

The double-blind, placebo-controlled trial was conducted at prenatal care centers in Argentina, Egypt, India, Peru, South Africa and Vietnam, and included more than 8,300 pregnant women whose dietary intake of calcium was less than 600 milligrams per day, which is 50 percent of the amount recommended during pregnancy. Half of the participants were given 1500 milligrams calcium per day, while the remainder received a placebo.

While the incidence of preeclampsia did not differ between the two groups, eclampsia and other severe complications including severe gestational hypertension were significantly lower among those who received calcium. Preterm and early preterm delivery were reduced by calcium in women under the age of twenty, a group that is at greatest risk of being deficient in the mineral and experiencing the resulting complications. Additionally, children of women who received calcium had a lower rate of death.

Coauthor Jose Villar, MD, states, "This large randomized trial in populations with low calcium intake demonstrates that while supplementation with 1.5 gm calcium/day did not result in a statistically significant decrease in the overall incidence of preeclampsia, calcium significantly decreased the risk of its more serious complications, including maternal and severe neonatal morbidity and mortality, as well as preterm delivery, the latter among young women."