Effect of Calcium Supplementation on Blood Lead Levels in Pregnancy: A Randomized Placebo-Controlled Trial

Background Prenatal lead exposure is associated with deficits in fetal growth and neurodevelopment. Calcium supplementation may attenuate fetal exposure by inhibiting mobilization of maternal bone lead and/or intestinal absorption of ingested lead. Objective Our goal was to evaluate the effect of 1,200 mg dietary calcium supplementation on maternal blood lead levels during pregnancy. Methods In a double-blind, randomized, placebo-controlled trial conducted from 2001 through 2003 in Mexico City, we randomly assigned 670 women in their first trimester of pregnancy to ingest calcium (n = 334) or placebo (n = 336). We followed subjects through pregnancy and evaluated the effect of supplementation on maternal blood lead, using an intent-to-treat analysis by a mixed-effects regression model with random intercept, in 557 participants (83%) who completed follow-up. We then conducted as-treated analyses using similar models stratified by treatment compliance. Results Adjusting for baseline lead level, age, trimester of pregnancy, and dietary energy and calcium intake, calcium was associated with an average 11% reduction (0.4 μg/dL) in blood lead level relative to placebo (p = 0.004). This reduction was more evident in the second trimester (−14%, p < 0.001) than in the third (−8%, p = 0.107) and was strongest in women who were most compliant (those who consumed ≥ 75% calcium pills; −24%, p < 0.001), had baseline blood lead > 5 μg/dL (−17%, p < 0.01), or reported use of lead-glazed ceramics and high bone lead (−31%, p < 0.01). Conclusion Calcium supplementation was associated with modest reductions in blood lead when administered during pregnancy and may constitute an important secondary prevention effort to reduce circulating maternal lead and, consequently, fetal exposure.