Calcium

High blood pressure with or without proteinuria is a major cause of maternal and perinatal morbidity and mortality worldwide. Preterm birth, a common association with hypertensive disorders, is the leading cause of early neonatal death and infant mortality, particularly in low-income countries. A number of observation studies led to the hypothesis that an increase in calcium intake during pregnancy might reduce the incidence of high blood pressure and pre-eclampsia among women with low calcium intake (Atallah et al . 2000). To date 12 randomised placebo controlled calcium supplementation trials during pregnancy have been published (Belizan et al . 1991, Villar et al . 1987, Purwar et al . 1996, Lopez-Jaramillo et al . 1997, Sanchez-Ramos et al . 1994, Lopez-Jaramillo et al . 1990, Lopez-Jaramillo et al . 1989, Villar & Repke 1990, Herrera et al. 1998, Crowther et al . 1999). 10 of them where analysed in a Cochrane review (Atallah et al . 2000) and the two more recent, in a recent discussion paper (Villar & Belizan 2000). In the Cochrane analysis, there was a slight reduction in blood pressure with calcium supplementation (RR 0.81 C.I. 0.74-0.89). In women at risk of hypertension and with low calcium intakes the effects were more marked with a RR of 0.35 (C.I. 0.21-0.57) and 0.49 (C.I. 0.38-0.62) respectively. The risk of pre-eclampsia also decreased after calcium supplementation (RR 0.70 C.I. 0.59-0.83). Here again the risk decrease was more important when women were either at risk of pre-eclampsia or when they had lower baseline calcium intakes with a RR of 0.22 (C.I. 0.11-0.43) and 0.32 (C.I. 0.21-0.49) respectively. There was no evidence that supplements decreased preterm delivery, although there was a reduction in risk among women at risk of hypertension. There was no effect of calcium supplementation on stillbirth or death before discharge from the hospital, but here were fewer babies with a low birth weight. Most of these findings have been replicated in the two more recently published trials (Herrera et al . 1998, Crowther et al . 1999). The present evidence supports the concept that calcium supplements during pregnancy can reduce pre-eclampsia when given to women with deficient calcium intake or when they are at risk for pre-eclampsia. The expected effect of supplementation might however be overestimated given that the total number of participants with low calcium intakes in all the analysed studies was rather small. There remains a need to conduct larger scale studies in calcium deficient populations. Calcium supplements during pregnancy seem however also to have a more sustained effect in the neonatal period and infancy. 591 children of a mean age of 7 years were followed up after their mothers where randomly assigned to a calcium supplement or a placebo group during pregnancy. The systolic blood pressure was lower in the children from the calcium supplemented group than in the placebo group. This effect was highest between the children who had a body mass index above the median of the population (Belizan et al . 1997).