Preliminary evidence of the effect of calcium supplementation on blood pressure in normal pregnant women

Calcium supplementation (other than for preventing or treating hypertension) for improving pregnancy and infant outcomes

BACKGROUND

Maternal nutrition during pregnancy is known to have an effect on fetal growth and development. It is recommended that women increase their calcium intake during pregnancy and lactation, although the recommended dosage varies among professionals. Currently, there is no consensus on the role of routine calcium supplementation for pregnant women other than for preventing or treating hypertension.

OBJECTIVES

To determine the effect of calcium supplementation on maternal, fetal and neonatal outcomes, excluding women with multiple gestation (other than for preventing or treating hypertension), including the occurrence of adverse effects.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (which includes results of comprehensive searches of CENTRAL, MEDLINE, Embase, CINAHL, two trials registers and relevant conference proceedings) on 3 December 2022. We also searched the reference lists of retrieved studies.

SELECTION CRITERIA

We considered all published, unpublished and ongoing randomised controlled trials (RCTs) comparing maternal, fetal and neonatal outcomes in pregnant women who received calcium supplementation versus placebo or no treatment. Cluster-RCTs were eligible for inclusion but none were identified. Quasi-RCTs and cross-over studies were not eligible for inclusion.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion. At least one review author assessed trials meeting the inclusion criteria for trustworthiness, consulting another review author in cases that were not immediately clear. Two review authors independently assessed the studies for risk of bias, extracted data, and checked trials for accuracy. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

Twenty-one studies met the inclusion criteria, but only 19 studies contributed data to the review. These 19 trials recruited 17,370 women, with 16,625 women included in the final analyses. The trials were generally at low risk of bias for randomisation and allocation concealment. We chose three outcomes for GRADE assessment: preterm birth less than 37 weeks, preterm birth less than 34 weeks and low birthweight (less than 2500 g). All trials compared calcium supplementation with placebo or no treatment with 17 trials comparing high-dose calcium (greater than 1000 mg/day). Calcium supplementation probably slightly reduces the risk of preterm birth less than 37 weeks (average risk ratio (RR) 0.80, 95% confidence interval (CI) 0.65 to 0.99; 11 trials, 15,379 women; moderate-certainty evidence), but probably has little effect on the risk of preterm birth less than 34 weeks (average RR 1.03, 95% CI 0.79 to 1.35; 3 trials, 5569 women; moderate-certainty evidence), and may have little or no effect on low birthweight (less than 2500 g) (average RR 0.93, 95% CI 0.81 to 1.07; 6 trials, 14,162 women; low-certainty evidence; 1 study reported low birthweight (less than 2500 g) but recorded 0 events in both groups. Thus, the RR and CIs were calculated from 5 studies rather than 6). We downgraded the evidence for imprecision (wide CIs crossing the line of no effect) and inconsistency (high levels of heterogeneity between the studies). There was no evidence that calcium supplementation had any effect on maternal weight gain during pregnancy; increasing bone mineral density in pregnant women; rate of intrauterine growth restriction; perinatal mortality; stillbirth or fetal death rate; increase birth length or fetal head circumference; and adverse effects such as postpartum haemorrhage, gall stones, gastrointestinal symptoms, headache, urinary stones, urinary tract infection or impaired renal function.

AUTHORS' CONCLUSIONS

This review indicates that calcium supplementation probably reduces preterm birth before 37 weeks. There are no clear additional benefits to calcium supplementation in preterm birth before 34 weeks or prevention of low birthweight. Large multicentre trials to detect the effect of calcium supplementation on fetal birthweight and preterm birth before 34 weeks as the primary outcomes are needed. Further research into the short- and long-term effects of calcium supplementation would also be beneficial.

The association between daily 500 mg calcium supplementation and lower pregnancy-induced hypertension risk in Bangladesh

BACKGROUND

Evidence suggests that daily supplementation of 1500 to 2000 mg of calcium during pregnancy reduces pregnancy-induced hypertension (PIH). However, the evidence on the efficacy of low-dose calcium supplementation on PIH is limited. This paper assesses the longitudinal correlation between low-dose calcium intake (500 mg daily) and change in blood pressure during pregnancy among a homogeneous population in terms of hypertension and pre-eclampsia.

METHODS

The study followed a retrospective cohort study design, and was carried out among 11,387 pregnant women from 10 rural upazilas (sub-districts) of Bangladesh where maternal nutrition initiative (MNI), implemented by Building Resources Across Communities (BRAC), was ongoing. The modified Poisson regression model was used to estimate the association (risk ratio) between consumption of calcium tablets and PIH.

RESULTS

The present research found that women who consumed 500 mg/d calcium tablets for more than 6 months during their pregnancy had a 45% lower risk of developing hypertension compared to those who consumed less calcium (RR = 0.55, 95% CI = 0.33-0.93).

CONCLUSIONS

Daily supplementation of 500 mg oral calcium during pregnancy for at least 180 tablets is associated with a considerably reduced risk of PIH, but this study is unable to confirm whether this association is causal. The causal relationship needs to be confirmed through a large scale randomized controlled trial.

Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

BACKGROUND

Pre-eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of pre-eclampsia, and may help to prevent preterm birth. This is an update of a review last published in 2014.

OBJECTIVES

To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes.

SEARCH METHODS

We searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (18 September 2017), and reference lists of retrieved studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs), including cluster-randomised trials, comparing high-dose calcium supplementation (at least 1 g daily of calcium) during pregnancy with placebo. For low-dose calcium we included quasi-randomised trials, trials without placebo, trials with cointerventions and dose comparison trials.

DATA COLLECTION AND ANALYSIS

Two researchers independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. Two researchers assessed the evidence using the GRADE approach.

MAIN RESULTS

We included 27 studies (18,064 women). We assessed the included studies as being at low risk of bias, although bias was frequently difficult to assess due to poor reporting and inadequate information on methods.High-dose calcium supplementation (≥ 1 g/day) versus placeboFourteen studies examined this comparison, however one study contributed no data. The 13 studies contributed data from 15,730 women to our meta-analyses. The average risk of high blood pressure (BP) was reduced with calcium supplementation compared with placebo (12 trials, 15,470 women: risk ratio (RR) 0.65, 95% confidence interval (CI) 0.53 to 0.81; I² = 74%). There was also a reduction in the risk of pre-eclampsia associated with calcium supplementation (13 trials, 15,730 women: average RR 0.45, 95% CI 0.31 to 0.65; I² = 70%; low-quality evidence). This effect was clear for women with low calcium diets (eight trials, 10,678 women: average RR 0.36, 95% CI 0.20 to 0.65; I² = 76%) but not those with adequate calcium diets. The effect appeared to be greater for women at higher risk of pre-eclampsia, though this may be due to small-study effects (five trials, 587 women: average RR 0.22, 95% CI 0.12 to 0.42). These data should be interpreted with caution because of the possibility of small-study effects or publication bias. In the largest trial, the reduction in pre-eclampsia was modest (8%) and the CI included the possibility of no effect.The composite outcome maternal death or serious morbidity was reduced with calcium supplementation (four trials, 9732 women; RR 0.80, 95% CI 0.66 to 0.98). Maternal deaths were no different (one trial of 8312 women: one death in the calcium group versus six in the placebo group). There was an anomalous increase in the risk of HELLP syndrome in the calcium group (two trials, 12,901 women: RR 2.67, 95% CI 1.05 to 6.82, high-quality evidence), however, the absolute number of events was low (16 versus six).The average risk of preterm birth was reduced in the calcium supplementation group (11 trials, 15,275 women: RR 0.76, 95% CI 0.60 to 0.97; I² = 60%; low-quality evidence); this reduction was greatest amongst women at higher risk of developing pre-eclampsia (four trials, 568 women: average RR 0.45, 95% CI 0.24 to 0.83; I² = 60%). Again, these data should be interpreted with caution because of the possibility of small-study effects or publication bias. There was no clear effect on admission to neonatal intensive care. There was also no clear effect on the risk of stillbirth or infant death before discharge from hospital (11 trials, 15,665 babies: RR 0.90, 95% CI 0.74 to 1.09).One study showed a reduction in childhood systolic BP greater than 95th percentile among children exposed to calcium supplementation in utero (514 children: RR 0.59, 95% CI 0.39 to 0.91). In a subset of these children, dental caries at 12 years old was also reduced (195 children, RR 0.73, 95% CI 0.62 to 0.87).Low-dose calcium supplementation (< 1 g/day) versus placebo or no treatmentTwelve trials (2334 women) evaluated low-dose (usually 500 mg daily) supplementation with calcium alone (four trials) or in association with vitamin D (five trials), linoleic acid (two trials), or antioxidants (one trial). Most studies recruited women at high risk for pre-eclampsia, and were at high risk of bias, thus the results should be interpreted with caution. Supplementation with low doses of calcium reduced the risk of pre-eclampsia (nine trials, 2234 women: RR 0.38, 95% CI 0.28 to 0.52). There was also a reduction in high BP (five trials, 665 women: RR 0.53, 95% CI 0.38 to 0.74), admission to neonatal intensive care unit (one trial, 422 women, RR 0.44, 95% CI 0.20 to 0.99), but not preterm birth (six trials, 1290 women, average RR 0.83, 95% CI 0.34 to 2.03), or stillbirth or death before discharge (five trials, 1025 babies, RR 0.48, 95% CI 0.14 to 1.67).High-dose (=/> 1 g) versus low-dose (< 1 g) calcium supplementationWe included one trial with 262 women, the results of which should be interpreted with caution due to unclear risk of bias. Risk of pre-eclampsia appeared to be reduced in the high-dose group (RR 0.42, 95% CI 0.18 to 0.96). No other differences were found (preterm birth: RR 0.31, 95% CI 0.09 to 1.08; eclampsia: RR 0.32, 95% CI 0.07 to 1.53; stillbirth: RR 0.48, 95% CI 0.13 to 1.83).

AUTHORS' CONCLUSIONS

High-dose calcium supplementation (≥ 1 g/day) may reduce the risk of pre-eclampsia and preterm birth, particularly for women with low calcium diets (low-quality evidence). The treatment effect may be overestimated due to small-study effects or publication bias. It reduces the occurrence of the composite outcome 'maternal death or serious morbidity', but not stillbirth or neonatal high care admission. There was an increased risk of HELLP syndrome with calcium supplementation, which was small in absolute numbers.The limited evidence on low-dose calcium supplementation suggests a reduction in pre-eclampsia, hypertension and admission to neonatal high care, but needs to be confirmed by larger, high-quality trials.

Calcium supplementation (other than for preventing or treating hypertension) for improving pregnancy and infant outcomes

BACKGROUND

Maternal nutrition during pregnancy is known to have an effect on fetal growth and development. It is recommended that women increase their calcium intake during pregnancy and lactation, although the recommended dosage varies among professionals. Currently, there is no consensus on the role of routine calcium supplementation for pregnant women other than for preventing or treating hypertension.

OBJECTIVES

To determine the effect of calcium supplementation on maternal, fetal and neonatal outcomes (other than for preventing or treating hypertension) as well as any possible side effects.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30th September 2014).

SELECTION CRITERIA

We considered all published, unpublished and ongoing randomised controlled trials (RCTs) comparing maternal, fetal and neonatal outcomes in pregnant women who received calcium supplementation versus placebo or no treatment. Cluster-RCTs were eligible for inclusion but none were identified. Quasi-RCTs and cross-over studies were not eligible for inclusion.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy.

MAIN RESULTS

Twenty-five studies met the inclusion criteria, but only 23 studies contributed data to the review. These 23 trials recruited 18,587 women, with 17,842 women included in final analyses. There were no statistically significant differences between women who received calcium supplementation and those who did not in terms of reducing preterm births less than 37 weeks' gestation (risk ratio (RR) 0.86, 95% confidence interval (CI) 0.70 to 1.05; 13 studies, 16,139 women; random-effects model) or less than 34 weeks' gestation (RR 1.04, 95% CI 0.80 to 1.36; four trials, 5669). Most studies were of low risk of bias. We conducted sensitivity analysis for the outcome of preterm birth less than 37 weeks by removing two trials with unclear risk of bias for allocation concealment; the results then favoured treatment with calcium supplementation (RR 0.80, 95% CI 0.65 to 0.99; 11 trials, 15,379 women). There was no significant difference in infant low birthweight between the two treatment groups (RR 0.93, 95% CI 0.81 to 1.07; six trials, 14,162 infants; random-effects model). However, when compared to the control group, women in the calcium supplementation group gave birth to slightly heavier birthweight infants (mean difference 56.40, 95% CI 13.55 to 99.25; 21 trials, 9202 women; random-effects model).Three outcomes were chosen for assessment with the GRADE software: preterm birth less than 37 weeks; preterm birth less than 34 weeks; and low birthweight less than 2500 g. Evidence for these outcomes was assessed as of moderate quality.

AUTHORS' CONCLUSIONS

This review indicates that there are no clear additional benefits to calcium supplementation in prevention of preterm birth or low infant birthweight. While there was a statistically significant difference of 56 g identified in mean infant birthweight, there was significant heterogeneity identified, and the clinical significance of this difference is uncertain.

Essential pre-pregnancy and pregnancy interventions for improved maternal, newborn and child health

The statistics related to pregnancy and its outcomes are staggering: annually, an estimated 250000-280000 women die during childbirth. Unfortunately, a large number of women receive little or no care during or before pregnancy. At a period of critical vulnerability, interventions can be effectively delivered to improve the health of women and their newborns and also to make their pregnancy safe. This paper reviews the interventions that are most effective during preconception and pregnancy period and synergistically improve maternal and neonatal outcomes. Among pre-pregnancy interventions, family planning and advocating pregnancies at appropriate intervals; prevention and management of sexually transmitted infections including HIV; and peri-conceptual folic-acid supplementation have shown significant impact on reducing maternal and neonatal morbidity and mortality. During pregnancy, interventions including antenatal care visit model; iron and folic acid supplementation; tetanus Immunisation; prevention and management of malaria; prevention and management of HIV and PMTCT; calcium for hypertension; anti-Platelet agents (low dose aspirin) for prevention of Pre-eclampsia; anti-hypertensives for treating severe hypertension; management of pregnancy-induced hypertension/eclampsia; external cephalic version for breech presentation at term (>36 weeks); management of preterm, premature rupture of membranes; management of unintended pregnancy; and home visits for women and children across the continuum of care have shown maximum impact on reducing the burden of maternal and newborn morbidity and mortality. All of the interventions summarized in this paper have the potential to improve maternal mortality rates and also contribute to better health care practices during preconception and periconception period.

Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

BACKGROUND

Pre-eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of pre-eclampsia, and may help to prevent preterm birth.

OBJECTIVES

To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (28 March 2013) and contacted study authors for more data where possible. We updated the search in May 2014 and added the results to the 'Awaiting Classification' section of the review.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing high-dose (at least 1 g daily of calcium) or low-dose calcium supplementation during pregnancy with placebo or no calcium.

DATA COLLECTION AND ANALYSIS

We assessed eligibility and trial quality, extracted and double-entered data.

MAIN RESULTS

High-dose calcium supplementation (≥1 g/day)We included 14 studies in the review, however one study contributed no data. We included 13 high-quality studies in our meta-analyses (15,730 women). The average risk of high blood pressure (BP) was reduced with calcium supplementation compared with placebo (12 trials, 15,470 women: risk ratio (RR) 0.65, 95% confidence interval (CI) 0.53 to 0.81; I² = 74%). There was also a significant reduction in the risk of pre-eclampsia associated with calcium supplementation (13 trials, 15,730 women: RR 0.45, 95% CI 0.31 to 0.65; I² = 70%). The effect was greatest for women with low calcium diets (eight trials, 10,678 women: average RR 0.36, 95% CI 0.20 to 0.65; I² = 76%) and women at high risk of pre-eclampsia (five trials, 587 women: average RR 0.22, 95% CI 0.12 to 0.42; I² = 0%). These data should be interpreted with caution because of the possibility of small-study effect or publication bias.The composite outcome maternal death or serious morbidity was reduced (four trials, 9732 women; RR 0.80, 95% CI 0.65 to 0.97; I² = 0%). Maternal deaths were not significantly different (one trial of 8312 women: calcium group one death versus placebo group six deaths). There was an anomalous increase in the risk of HELLP (haemolysis, elevated liver enzymes and low platelets) syndrome (two trials, 12,901 women: RR 2.67, 95% CI 1.05 to 6.82; I² = 0%) in the calcium group, however, the absolute number of events was low (16 versus six).The average risk of preterm birth was reduced in the calcium group (11 trials, 15,275 women: RR 0.76, 95% CI 0.60 to 0.97; I² = 60%) and amongst women at high risk of developing pre-eclampsia (four trials, 568 women: average RR 0.45, 95% CI 0.24 to 0.83; I² = 60%), but no significant reduction in neonatal high care admission. There was no overall effect on the risk of stillbirth or infant death before discharge from hospital (11 trials 15,665 babies: RR 0.90, 95% CI 0.74 to 1.09; I² = 0%).One study showed a reduction in childhood systolic BP greater than 95th percentile among children exposed to calcium supplementation in utero (514 children: RR 0.59, 95% CI 0.39 to 0.91). In a subset of these children, dental caries at 12 years old was also reduced (195 children, RR 0.73, 95% CI 0.62 to 0.87). Low-dose calcium supplementation (< 1 g/day)We included 10 trials (2234 women) that evaluated low-dose supplementation with calcium alone (4) or in association with vitamin D (3), linoleic acid (2), or antioxidants (1). Most studies recruited women at high risk for pre-eclampsia, and were at high risk of bias, thus the results should be interpreted with caution. Supplementation with low doses of calcium significantly reduced the risk of pre-eclampsia (RR 0.38, 95% CI 0.28 to 0.52; I² = 0%). There was also a reduction in hypertension, low birthweight and neonatal intensive care unit admission.

AUTHORS' CONCLUSIONS

Calcium supplementation (≥ 1 g/day) is associated with a significant reduction in the risk of pre-eclampsia, particularly for women with low calcium diets. The treatment effect may be overestimated due to small-study effects or publication bias. It also reduces preterm birth and the occurrence of the composite outcome 'maternal death or serious morbidity'. We considered these benefits to outweigh the increased risk of HELLP syndrome, which was small in absolute numbers. The World Health Organization recommends calcium 1.5 g to 2 g daily for pregnant women with low dietary calcium intake.The limited evidence on low-dose calcium supplementation suggests a reduction in pre-eclampsia, but needs to be confirmed by larger, high-quality trials. Pending such results, in settings of low dietary calcium where high-dose supplementation is not feasible, the option of lower-dose supplements (500 to 600 mg/day) might be considered in preference to no supplementation.

Randomized, placebo-controlled, calcium supplementation trial in pregnant Gambian women accustomed to a low calcium intake: effects on maternal blood pressure and infant growth

BACKGROUND

Dietary calcium intake in rural Gambian women is very low (∼350 mg/d) compared with international recommendations. Studies have suggested that calcium supplementation of women receiving low-calcium diets significantly reduces risk of pregnancy hypertension.

OBJECTIVE

We tested the effects on blood pressure (BP) of calcium carbonate supplementation (1500 mg Ca/d) in pregnant, rural Gambian women.

DESIGN

The study was a randomized, double-blind, parallel, placebo-controlled supplementation trial from 20 wk of gestation (P20) until delivery (calcium: n = 330; placebo; n = 332). BP and anthropometric measures were taken at P20 and then 4 weekly until 36 wk of gestation (P36), and infant anthropometric measures were taken at 2, 13, and 52 wk postdelivery.

RESULTS

A total of 525 (calcium: n = 260; placebo: n = 265) women had BP measured at P36 and subsequently delivered a healthy term singleton infant. Mean compliance was 97%, and urinary calcium measures confirmed the group allocation. At P20, the mean (±SD) systolic blood pressure (SBP) was 101.2 ± 9.0 and 102.1 ± 9.3 mm Hg, and diastolic blood pressure (DBP) was 54.5 ± 7.3 and 55.8 ± 7.8 mm Hg, in the calcium and placebo groups, respectively. The intention-to-treat analysis that was adjusted for confounders showed no significant effect of calcium supplementation on the change between P20 and P36 (calcium compared with placebo; mean ± SEM) in SBP (-0.64 ± 0.65%; P = 0.3) or DBP (-0.22 ± 1.15%; P = 0.8). There was no significant effect of supplementation on BP, pregnancy weight gain, weight postpartum, or infant weight, length, and other measures of growth. However, the comparability of the original randomly assigned groups may have been compromised by the exclusion of 20.7% of women from the final analysis.

CONCLUSIONS

Calcium supplementation did not affect BP in pregnancy. This result may have been because the Gambian women were adapted to a low dietary calcium intake, and/or obesity, high gestational weight gain, high underlying BP, tobacco use, alcohol consumption, and sedentary lifestyles were rare. This trial was registered at the International Standard Randomized Controlled Trial Register (www.controlled-trials.com/mrct/) as ISRCTN96502494.

Calcium supplementation (other than for preventing or treating hypertension) for improving pregnancy and infant outcomes

BACKGROUND

Maternal nutrition during pregnancy is known to have an effect on fetal growth and development. It is recommended that women increase their calcium intake during pregnancy and lactation, although the recommended dosage varies among professionals. Currently, there is no consensus on the role of routine calcium supplementation for pregnant women other than for preventing or treating hypertension.

OBJECTIVES

To determine the effect of calcium supplementation on maternal, fetal and neonatal outcomes (other than for preventing or treating hypertension) as well as any possible side effects.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (17 March 2011).

SELECTION CRITERIA

We considered all published, unpublished and ongoing randomised controlled trials (RCTs) comparing maternal, fetal and neonatal outcomes in pregnant women who received calcium supplementation versus placebo or no treatment. We excluded quasi- and pseudo-RCTs.

DATA COLLECTION AND ANALYSIS

Two review authors identified studies for inclusion and extracted the data. Two review authors performed data analysis.

MAIN RESULTS

This review includes data from 21 studies (involving 16,602 women). There were no statistically significant differences between women who received calcium supplementation and those who did not in terms of reducing preterm births (less than 37 weeks' gestation) (risk ratio (RR) 0.90; 95% confidence interval (CI) 0.73 to 1.11; 12 studies, 15615 women; random-effects model) and also in less than 34 weeks' gestation (RR 1.11; 95% CI 0.84 to 1.46; three trials, 5145 women). There was no significant difference in infant low birth weight between the two groups (RR 0.91; 95% CI 0.72 to 1.16; four trials, 13449 infants; random-effects). However, compared to the control group, women in the calcium supplementation group gave birth to slightly heavier birth weight infants (mean difference (MD) 64.66 g; 95% CI 15.75 to 113.58; 19 trials, 8287 women; random-effects).

AUTHORS' CONCLUSIONS

Calcium supplementation is associated with a significant protective benefit in the prevention of pre-eclampsia, and should be used for this indication according to a previous review. This review indicates that there are no additional benefits for calcium supplementation in prevention of preterm birth or low infant birth weight. While there was a statistically significant difference of 80 g identified in mean infant birth weight, there was significant heterogeneity identified, and the clinical significance of this difference is uncertain.

Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

BACKGROUND

Pre-eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of pre-eclampsia through a number of mechanisms, and may help to prevent preterm birth.

OBJECTIVES

To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (May 2010) and contacted study authors.

SELECTION CRITERIA

Randomised trials comparing at least 1 g daily of calcium during pregnancy with placebo.

DATA COLLECTION AND ANALYSIS

We assessed eligibility and trial quality, extracted and double-entered data.

MAIN RESULTS

We included 13 studies of good quality (involving 15,730 women). The average risk of high blood pressure was reduced with calcium supplementation rather than placebo (12 trials, 15,470 women: risk ratio (RR) 0.65, 95% confidence interval (CI) 0.53 to 0.81). There was also a reduction in the average risk of pre-eclampsia associated with calcium supplementation (13 trials, 15,730 women: RR 0.45, 95% CI 0.31 to 0.65). The effect was greatest for high-risk women (five trials, 587 women: RR 0.22, 95% CI 0.12 to 0.42), and those with low baseline calcium intake (eight trials, 10,678 women: RR 0.36, 95% CI 0.20 to 0.65).The average risk of preterm birth was reduced in the calcium group overall (11 trials, 15,275 women: RR 0.76, 95% CI 0.60 to 0.97) and amongst women at high risk of developing pre-eclampsia recruited to four small trials (568 women: RR 0.45, 95% CI 0.24 to 0.83).There was no overall effect on the risk of stillbirth or death before discharge from hospital (11 trials 15,665 babies; RR 0.90, 95% CI 0.74 to 1.09). The composite outcome maternal death or serious morbidity was reduced (four trials, 9732 women; RR 0.80, 95% CI 0.65 to 0.97). Most of the women in these trials were low risk and had a low calcium diet. Maternal deaths were reported in only one trial. One death occurred in the calcium group and six in the placebo group, a difference which was not statistically significant (RR 0.17, 95% CI 0.02 to 1.39).Blood pressure in childhood has been assessed in two studies, only one of which is currently included: childhood systolic blood pressure greater than 95th percentile was reduced (514 children: RR 0.59, 95% CI 0.39 to 0.91).

AUTHORS' CONCLUSIONS

Calcium supplementation appears to approximately halve the risk of pre-eclampsia, to reduce the risk of preterm birth and to reduce the rare occurrence of the composite outcome 'death or serious morbidity'. There were no other clear benefits, or harms.

Vaso-active factors in pregnancy

Pregnancy results in profound physiological changes in the cardiovascular system, yet these changes are completely reversible. It is apparent that vaso-active factors, some as yet probably unidentified, which act as humoral or local autocrine or paracrine regulators of vasular resistance, play a major role in these cardio-vascular changes. This role may be heightened in pregnancy when there has to be a large increase in blood flow to the uterus and placenta while maintaining adequate flow to other vascular beds. Our knowledge of the mechanisms of action of these vaso-active factors and their interactions with each other still remains incomplete. Alterations in synthesis and action of these vaso-active factors may occur in pregnancies associated with pregnancy-induced hypertension, pre-eclampsia or intra-uterine growth retardation. Investigation of such alterations may help to elucidate the roles of vaso-active factors in both normal and pathological situations. The gestational hormones oestrogen and progesterone, are obviously prime candidates as overall regulators of the cardiovascular changes of pregnancy and as agents which alter the synthesis or action of other vaso-active factors. Currently, much attention is being focused on the role of local autocrine or paracrine vaso-active factors which may be produced by the endothelium or by the underlying vascular smooth muscle cells and alterations in their production or action in the hyptertensive disorders of pregnancy. The endothelium forms the largest endocrine organ within the body and so its importance in the mediation of vascular events should not be under-estimated. The principal objective of this review is to examine the roles of these many autocrine and paracrine vaso-active factors during pregnancy and their relation with the overall regulation of the vascular system. Changes which may occur and be involved in the aetiology of pre-eclampsia and growth retardation will also be examined.

Supplemental Calcium and Risk Reduction of Hypertension, Pregnancy-Induced Hypertension, and Preeclampsia: An Evidence-Based Review by the US Food and Drug Administration

The labeling of health claims that meet the significant scientific agreement (SSA) standard (authorized health claims) and qualified health claims on conventional foods and dietary supplements requires premarket approval by the US Food and Drug Administration (FDA). FDA conducts an evidence-based review to determine whether there is sufficient evidence to support an authorized or qualified health claim. An evidence-based review was conducted on the human intervention and observational studies evaluating the role of supplemental calcium in reducing the risk of hypertension, pregnancy-induced hypertension, and preeclampsia. This review provides FDA's evaluation of the current scientific evidence on the role of supplemental calcium in reducing the risk of these three end points. Based on this evidence-based review, the agency concluded that the relationship between calcium and risk of hypertension is inconsistent and inconclusive, and the relationship between calcium and risk of pregnancy-induced hypertension and preeclampsia is highly unlikely.

Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

BACKGROUND

Pre-eclampsia and eclampsia are common causes of serious morbidity and death. Calcium supplementation may reduce the risk of pre-eclampsia through a number of mechanisms, and may help to prevent preterm labour.

OBJECTIVES

To assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group Trials Register (February 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2005, Issue 4), and contacted study authors.

SELECTION CRITERIA

Randomised trials comparing at least one gram daily of calcium during pregnancy with placebo.

DATA COLLECTION AND ANALYSIS

We assessed eligibility and trial quality, extracted and double-entered data.

MAIN RESULTS

Twelve studies of good quality were included. The risk of high blood pressure was reduced with calcium supplementation rather than placebo (11 trials, 14,946 women: relative risk (RR) 0.70, 95% confidence interval (CI) 0.57 to 0.86). There was also a reduction in the risk of pre-eclampsia associated with calcium supplementation (12 trials, 15,206 women: RR 0.48, 95% CI 0.33 to 0.69). The effect was greatest for high-risk women (5 trials, 587 women: RR 0.22, 95% CI 0.12 to 0.42), and those with low baseline calcium intake (7 trials, 10,154 women: RR 0.36, 95% CI 0.18 to 0.70). The composite outcome maternal death or serious morbidity was reduced (4 trials, 9732 women; RR 0.80, 0.65 to 0.97). Almost all the women in these trials were low risk and had a low calcium diet. Maternal deaths were reported in only one trial. One death occurred in the calcium group and six in the placebo group, a difference which was not statistically significant (RR 0.17, 95% CI 0.02 to 1.39). There was no overall effect on the risk of preterm birth (10 trials, 14,751 women: RR 0.81, 95% CI 0.64 to 1.03), or stillbirth or death before discharge from hospital (10 trials 15,141 babies; RR 0.89, 95% CI 0.73 to 1.09).Blood pressure in childhood has been assessed in one study: childhood systolic blood pressure greater than 95th percentile was reduced (514 children: RR 0.59, 95% CI 0.39 to 0.91).

AUTHORS' CONCLUSIONS

Calcium supplementation appears to almost halve the risk of pre-eclampsia, and to reduce the rare occurrence of the composite outcome 'death or serious morbidity'. There were no other clear benefits, or harms.

Correlation of maternal serum high-sensitive C-reactive protein levels with biochemical and clinical parameters in preeclampsia

OBJECTIVE

To investigate the relationship between serum high sensitive C-reactive protein (hsCRP) levels and biochemical and clinical parameters in preeclampsia (PE).

STUDY DESIGN

This cross-sectional study included 20 women with PE and 20 healthy pregnant women. They were recruited in the third trimester of pregnancy at the Firat University, Firat Medical Center, Department of Obstetric and Gynaecology in Elazig province. The standard biochemical and hematological parameters were measured by an advanced auto analyzer. Venous blood samples were collected at admission to the hospital at least 6h before delivery for measurement of hsCRP by a high sensitive immunonephelometric method.

RESULTS

Hemoglobin, serum hsCRP, creatinine, aspartat and alanine transaminase, lactate dehydrogenase, blood urea nitrogen and urine protein excretion were higher, and serum calcium levels were lower in patients with PE compared to control group values. In the preeclampsia group, correlation analysis tests showed a strong positive correlation between serum hsCRP levels and diastolic blood pressures (r=0.9, p=0.05, n=20) and urinary protein excretion (r=0.8, p=0.05, n=20), and a negative correlation between serum hsCRP and weight (r=-0.6, p=0.02, n=20) and length (r=-0.5, p=0.05, n=20) of the newborns. Serum hsCRP levels were also negatively correlated with weights (r=0.5, p=0.02, n=20) and lengths (r=0.5, p=0.05, n=20) of the newborns in the control group.

CONCLUSIONS

Serum hsCRP levels increase in women with PE. Elevated serum levels of hsCRP in preeclamptic women are correlated with clinical and biochemical parameters of PE. Determination of serum hsCRP levels may be used as a marker for the severity of PE.

Nutrient involvement in preeclampsia

Preeclampsia is a pregnancy-specific condition that increases maternal and infant mortality and morbidity. It is diagnosed by new-onset increased blood pressure and proteinuria during gestation; for many years these markers were the sole targets for study. More recently, increased attention to the multisystemic nature of the syndrome with involvement of almost all organs, activation of coagulation and increased sensitivity to pressor agents has expanded understanding of the disorder. The epidemiology of preeclampsia, being more common in poor women, long ago suggested that nutrients might be involved in the disorder. Numerous conflicting hypotheses were advanced but the testing of these hypotheses has either been done poorly or not at all. Review of the available data indicates very few studies that provide useful insights. In many studies the syndrome is poorly defined and in most studies nutritional data (questionnaires or biomarkers) are obtained on women with the clinical syndrome. In overtly preeclamptic women it is impossible to decipher cause from effect. Nonetheless, current concepts of the genesis of preeclampsia that include endothelial dysfunction, inflammatory activation, oxidative stress and predisposing maternal factors provide targets for well-designed nutritional investigation. In this review the current concepts of the pathogenesis of preeclampsia are reviewed and available data are assessed in light of these concepts. Targets for nutritional investigation based on the current knowledge of pathophysiology are suggested.

Association of very low birth weight with calcium levels in drinking water

It has been hypothesized that calcium supplementation can reduce smooth muscle contractibility and tone and that this effect can be clinically manifested by a reduction in blood pressure and a reduction in the incidence of premature delivery. Calcium supplementation has been reported to reduce blood pressure in pregnant and nonpregnant women. We performed a study to examine the relationship between the levels of calcium in drinking water and the risk of delivering a child of very low birth weight (VLBW). The study population comprised 1781 women residing in 252 municipalities who had a first-parity singleton birth between January 1, 1993 and December 31, 1997 and for whom complete information on maternal age, education, gestational age, birth weight, and sex of the baby were available. Data on calcium levels were obtained from the Taiwan Water Supply Corporation. The results of our study provide evidence that there is significant protective effect of calcium intake from drinking water on the risk of delivering a VLBW baby. This is an important finding for the Taiwan water industry and human health.

Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems

BACKGROUND

Calcium supplementation may prevent high blood pressure through a number of mechanisms and may help to prevent preterm labour.

OBJECTIVES

The objective of this review was to assess the effects of calcium supplementation during pregnancy on hypertensive disorders of pregnancy and related maternal and child adverse outcomes.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (October 2001) and the Cochrane Controlled Trials Register (Issue 3, 2001) and we contacted study authors.

SELECTION CRITERIA

Randomised trials comparing at least one gram daily of calcium during pregnancy with placebo.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed. Data extraction was carried out and double entered.

MAIN RESULTS

Eleven studies were included, all of good quality. There was a modest reduction in high blood pressure with calcium supplementation (relative risk 0.81, 95% confidence interval 0.74 to 0.89). The effect was greatest for women at high risk of hypertension (relative risk 0.45, 95% confidence interval 0.31 to 0.66) and those with low baseline dietary calcium (relative risk 0.49, 95% confidence interval 0.38 to 0.62). There was also a modest reduction in the risk of pre-eclampsia with calcium supplementation (relative risk 0.68, 95% confidence interval 0.57 to 0.81). The effect was greatest for women at high risk of hypertension (relative risk 0.21, 95% confidence interval 0.11 to 0.39) and those with low baseline calcium intake (relative risk 0.32, 95% confidence interval 0.21 to 0.49). There was no overall effect on the risk of preterm delivery, although there was a reduction in risk amongst women at high risk of hypertension (relative risk 0.42, 95% confidence interval 0.23 to 0.78). There was no evidence of any effect of calcium supplementation on stillbirth or death before discharge from hospital. There were fewer babies with birthweight < 2500g (RR 0.83, 95% CI 0.71-0.98). In one study, childhood systolic blood pressure > 95th percentile was reduced (RR 0.59, 95% CI 0.39-0.91).

REVIEWER'S CONCLUSIONS

Calcium supplementation appears to be beneficial for women at high risk of gestational hypertension and in communities with low dietary calcium intake. Optimum dosage requires further investigation.

Dietary calcium and pregnancy-induced hypertension: is there a relation?

The evidence that calcium plays a role in the etiology, prevention, and treatment of pregnancy-induced hypertension (PIH) is reviewed. The precise factors involved in the pathogenesis of PIH are unclear, but several alterations in calcium metabolism have been identified. Epidemiologic data suggest an inverse correlation between dietary calcium intake and incidence of PIH. Although evidence suggests a possible beneficial effect of supplemental calcium, contradictions persist in clinical trials of pregnant women. Presently, there is insufficient evidence to support routine calcium supplementation of all pregnant women. However, high-risk groups, such as pregnant teens, populations with inadequate calcium intake, and women at risk of developing PIH, may benefit from consuming additional dietary calcium.

Fetal growth and consequences for later life

There is evidence that an abnormal intrauterine environment has consequences for later life. Intrauterine growth retardation is associated with low insulin secretion during fetal life and probably a reduced development of insulin receptors. In later life these alterations can induce insulin resistance. Macrosomia is associated with an increased insulin secretion during fetal life and exhaustion of the insulin producing B cells. In later life a reduced insulin secretion is found. The working mechanisms have been explored in experimental studies. Normalisation of the diabetic intrauterine milieu can prevent consequences in later life. There are also indications that vascular changes in later life can be reduced by anti-oxidantia. In the human intrauterine growth retardation is related in later life with insulin resistance, vascular diseases and preeclampsia; macrosomia is related with gestational diabetes and breastcarcinoma.

Regulation of blood pressure with calcium-dependent dopamine synthesizing system in the brain and its related phenomena

The effects of calcium on blood pressure regulation remain controversial. Although the mechanism by which calcium increases blood pressure when it is given intravenously and acutely has been elucidated, that by which calcium reduces blood pressure when it is supplemented chronically and slightly through daily diet is unclear. From a number of animal experiments concerning the effects of calcium on blood pressure, we believe that calcium ions have two separate roles in the regulation of blood pressure through both central and peripheral systems: (1) calcium ions reduce blood pressure through a central, calcium/calmodulin-dependent dopamine-synthesizing system and (2) calcium ions increase blood pressure through an intracellular, calcium-dependent mechanism in the peripheral vasculature. These concepts were applied to elucidate the mechanisms underlying hypertension in spontaneously hypertensive rats (SHR) and changes in blood pressure in other experimental animals, and the following conclusions were reached. The decrease of the serum calcium level in spontaneously hypertensive rats (SHR) causes a decrease in calcium/calmodulin-dependent dopamine synthesis in the brain. The subsequent low level of brain dopamine induces hypertension. The increase in susceptibility to epileptic convulsions and the occurrence of hypertension in epileptic mice (El mice) may be linked through a lowering of calcium-dependent dopamine synthesis in the brain, and epilepsy and hypertension may be associated. Exercise leads to increases in calcium-dependent dopamine synthesis in the brain, and the increased dopamine levels induce physiological changes, including a decrease in blood pressure. Cadmium which is not distinguished from calcium by calmodulin, activates calmodulin-dependent functions in the brain, and increased dopamine levels may decrease blood pressure. In this report, our studies are considered in light of reports from many other laboratories.

Calcium supplementation and prevention of pregnancy induced hypertension

In a randomized controlled trial 201 healthy nulliparous women were randomly allocated by means of a computer generated randomization list. From 20 weeks of gestation until delivery they received either 2 g of oral elemental calcium (n = 103) per day or an identical placebo (n = 98). Eleven women (5.47%) were lost to follow-up after randomization. The study groups were very similar at the time of randomization; with respect to several clinical and demographic variables. Treatment compliance was very similar in both groups as was determined by pill count. The rate of pregnancy induced hypertension was lower in the calcium group than in the placebo group 8.24%; vs 29.03%; (RR = 0.28; 95% CI 0.14-0.59). The incidence of gestational hypertension was 6.18% in the calcium group and 17.20% in the placebo group (RR = 0.28; 95% CI 0.08-0.80), and the incidence of preeclampsia was 2.06% in the calcium group and 11.82% in the placebo group (RR = 0.13; 95% CI 0.01-0.64). In conclusion calcium supplementation given in pregnancy to nulliparous women reduces the incidence of pregnancy induced hypertension.

Complexity and complicity in eclampsia: barriers or bridges?

The aetiology of pre-eclampsia-eclampsia remains largely unclarified, despite over 100 years of systematic study. The assumption that the triggering event is linear and amenable to reductionist techniques has characterized these efforts. The main purpose of this paper is to show that complexity and complicity characterize most pathophysiological processes in pre-eclampsia-eclampsia, a situation suggesting that similar mechanisms must exist at the origin of the disease. The unique configuration of the intervillous space and the intensity of energy transference through the fetomaternal interface offer many dysfunctional possibilities, even in clinically normal pregnancies. The most characteristic seem to be: the shedding and deportation of trophoblast, the fragmentation of villi, the escape of fetal blood, and events associated with trophoblast damage, degeneration and death. The pathogenic potential of these natural processes seems to depend on the association with amplifiers and permissive factors, which vary from person to person and from time to time. Thus, considering the convergence of multiple factors and the presence of nonlinearity in some of their interactions as a plausible working hypothesis, further exploration on this subject should adhere to the rules of this different reality. To find the best possible method of inquiry and to recognize its limitations will be the surest way to avoid failure.

Calcium metabolism, calcium supplementation and hypertensive disorders of pregnancy

In recent years growing attention has been directed towards the possible role of calcium in the development of pregnancy-induced hypertension and preeclampsia. Several studies describe calcium metabolism in normal and hypertensive pregnancy, but so far, they have shown discrepant and inconsistent results. Intracellular free calcium, which plays an important role in vascular smooth muscle contraction, has been claimed as a pathogenic factor in hypertensive disorders of pregnancy. Although there is discordance in the data, a possible role of intracellular calcium in the development of hypertensive disorders of pregnancy cannot be excluded. Observational studies in pregnant women suggest an inverse association between calcium intake and the incidence of hypertensive disorders of pregnancy. Despite large methodological differences, the results from the calcium supplementation trials support this finding. Although it is rather difficult to isolate the effect of calcium intake from the intake of other mineral elements, results from calcium supplementation trials are supportive for calcium being the most important. Proposed mechanisms by which calcium supplementation may lower blood pressure involve changes in parathyroid hormone (PTH) level, the renin-angiotensin system and calcium as a modifier of vascular agent regulation, but none of these have yet been elucidated. At present, circumstantial evidence suggest a positive role for calcium in the prevention of hypertensive disorders of pregnancy, but definite evidence is lacking and further research is warranted.

Dietary calcium and blood pressure in experimental models of hypertension. A review

More than 80 studies have reported lowered blood pressure after dietary calcium enrichment in experimental models of hypertension. The evidence presented here suggests that dietary calcium may act concurrently through a number of physiological mechanisms to influence blood pressure. The importance of any given mechanism may vary depending on the experimental model under consideration. Supplemental dietary calcium is associated with reduced membrane permeability, increased Ca(2+)-ATPase and Na,K-ATPase, and reduced intracellular calcium. These results suggest that supplemental calcium may limit calcium influx into the cell and improve the ability of the VSMC to extrude calcium. This could be a direct effect of calcium on the VSMC or an indirect effect mediated hormonally. The calcium-regulating hormones have all been found to have vasoactive properties and therefore may influence blood pressure. Furthermore, CGRP and the proposed parathyroid hypertensive factor are both vasoactive substances that are responsive to dietary calcium. Therefore, diet-induced variations in calcium-regulating hormones may influence blood pressure. Modulation of the sympathetic nervous system is another important way that dietary calcium can influence blood pressure. There is evidence of altered norepinephrine levels in the hypothalamus as a consequence of manipulations of dietary calcium as well as changes in central sympathetic nervous system outflow. Dietary calcium has also been shown to specifically modify alpha 1-adrenergic receptor activity in the periphery. In some experimental models of hypertension, dietary calcium may alter blood pressure by changing the metabolism of other electrolytes. For example, the ability of calcium to prevent sodium chloride-induced elevations in blood pressure may be attributed to natriuresis. However, natriuresis does not account for all of the interactive effects of calcium and sodium chloride on blood pressure. Sodium chloride-induced hypertension may be due in part to calcium wasting and subsequent elevation of calcium-regulating hormones. Chloride is an important mediator of this effect because it appears that sodium does not cause calcium wasting when it is not combined with chloride. More attention to the central nervous system effects of dietary calcium is needed. Not only can calcium itself influence neural function, but many of the calcium-regulating hormones appear to affect the central nervous system. The influence of calcium and calcium-regulating hormones on central nervous system activity may have important implications for blood pressure regulation and also may extend to other aspects of physiology and behavior.

Calcium supplementation to prevent hypertensive disorders of pregnancy

BACKGROUND

Calcium supplementation has been reported to reduce blood pressure in pregnant and nonpregnant women. We undertook this prospective study to determine the effect of calcium supplementation on the incidence of hypertensive disorders of pregnancy (gestational hypertension and preeclampsia) and to determine the value of urinary calcium levels as a predictor of the response.

METHODS

We studied 1194 nulliparous women who were in the 20th week of gestation at the beginning of the study. The women were randomly assigned to receive 2 g per day of elemental calcium in the form of calcium carbonate (593 women) or placebo (601 women). Urinary excretion of calcium and creatinine was measured before calcium supplementation was begun. The women were followed to the end of their pregnancies, and the incidence of hypertensive disorders of pregnancy was determined.

RESULTS

The rates of hypertensive disorders of pregnancy were lower in the calcium group than in the placebo group (9.8 percent vs. 14.8 percent; odds ratio, 0.63; 95 percent confidence interval, 0.44 to 0.90). The risk of these disorders was lower at all times during gestation, particularly after the 28th week of gestation (P = 0.01 by life-table analysis), in the calcium group than in the placebo group, and the risk of both gestational hypertension and preeclampsia was also lower in the calcium group. Among the women who had low ratios of urinary calcium to urinary creatinine (less than or equal to 0.62 mmol per millimole) during the 20th week of gestation, those in the calcium group had a lower risk of hypertensive disorders of pregnancy (odds ratio, 0.56; 95 percent confidence interval, 0.29 to 1.09) and less of an increase in diastolic and systolic blood pressure than the placebo group. The pattern of response was similar among the women who had a high ratio of urinary calcium to urinary creatinine during the 20th week of gestation, but the differences were smaller.

CONCLUSIONS

Pregnant women who receive calcium supplementation after the 20th week of pregnancy have a reduced risk of hypertensive disorders of pregnancy.

Prevention and treatment of pregnancy-associated hypertension: what have we learned in the last 10 years?

High blood pressure (BP) complicates approximately 10% of all pregnancies. Hypertension in pregnancy falls into four categories: (1) preeclampsia-eclampsia, (2) chronic hypertension of whatever cause, (3) preeclampsia-eclampsia superimposed to chronic hypertension or renal disease, and (4) transient or late hypertension (gestational hypertension). Preeclampsia, the association of hypertension, proteinuria, and edema, accounts for more than 50% of all the hypertensive disorders of pregnancy and is a major cause of fetal and maternal morbidity and mortality. Unfortunately, distinguishing between preeclampsia and other causes of hypertension on clinical grounds can be difficult because of the lack of specific tests for differential diagnosis. Increased vascular resistance has been claimed as the primary cause of preeclampsia; however, a variable hemodynamic profile with relatively high cardiac outputs, normal filling pressures, and inappropriately high systemic vascular resistances is now reported by most investigators. Imbalance between vasodilator and vasoconstrictor eicosanoids may account for platelet activation and increased responsiveness to pressor peptides. Altered prostacyclin (PGI2) to thromboxane A2 (TxA2) ratio in maternal uteroplacental vascular bed may favor local platelet activation and vasoconstriction contributing to placental insufficiency and fetal distress. Alternatively, recent evidence seems to suggest that fetal umbilical placental circulation may be the site of the primary vascular injury. Whether low-dose aspirin prevents preeclampsia because it inhibits the excessive maternal TxA2 or whether the partial inhibition of fetal TxA2 is also of therapeutic value remains to be established. Treatment of severe hypertension in pregnancy is probably important to prevent cardiac failure or cerebrovascular accidents in the mother. The need for pharmacological therapy of mild to moderate hypertension is still debated, since no formal studies are available to clarify whether pharmacological treatment in such instances effectively reduces maternal or fetal risk. For the treatment of preeclampsia, hydralazine and nifedipine may be used when delivery is not applicable. Labetalol and diazoxide are effective for hypertensive emergencies. Life-threatening hypertension that does not respond to more conventional therapy is an indication for the use of sodium nitroprusside. For chronic hypertension, alpha-methyldopa remains the treatment of choice; if ineffective, hydralazine or beta-blockers are suitable. Effectiveness and safety of other molecules remain elusive.

Vascular reactivity in normal and abnormal gestation

Preeclampsia is characterized by enhanced pressor responsiveness to angiotensin II. This report summarizes studies by our laboratory to investigate possible roles for calcium, sodium, membrane pumps, and the vasoactive hormones, atrial natriuretic peptide (hANP) and endothelin, in modulating the change in vascular reactivity characteristic of preeclampsia. Urinary calcium excretion, 1 alpha-25(OH)2D3 levels, and serum free calcium levels were all decreased, whereas parathyroid hormone levels and intraplatelet calcium concentrations were increased in women with preeclampsia. Erythrocyte sodium content was elevated, while red blood cell membrane Na-K-ATPase activity was decreased in patients with severe disease. Preeclamptics also had elevated levels of hANP, which failed to increase further when saline was infused or when blood pressure was increased transiently with angiotensin II administration. Finally, endothelin levels that are reduced in normal gestation, were increased in preeclampsia. While the cause of increased vascular reactivity is still unclear, there appear to be changes in the intracellular cation environment, combined with loss of compensating mechanisms, both at the membrane and humoral level, as well as enhanced concentrations of a potent vasoconstrictor in blood; all which lead to increases in vasoreactivity and blood pressure in preeclampsia.

The clinical utility of the roll-over test in predicting pregnancy-induced hypertension in a high-risk Andean population

The utility of the roll-over test (ROT) as a prognostic tool for predicting pregnancy-induced hypertension (PIH) was examined in primiparas in Quito, Ecuador. In Study I, 14 of 16 subjects with a +ROT developed PIH (positive predictive value (PPV) = 88%); only 2 of 27 subjects with a -ROT developed PIH (negative predictive value (NPV) = 92.5%). In Study II (n = 66), the PPV and NPV were 71.4% and 78.6%, respectively. Data from these and previous studies indicate that although the ROT is not a perfect predictor, its advantages recommend usage in populations with high PIH-associated maternal and perinatal mortality.

The Canadian consensus report on non-pharmacological approaches to the management of high blood pressure

The Canadian Consensus Conference on Non-Pharmacological Approaches to the Management of High Blood Pressure reviewed in March, 1989 on its meeting in Halifax, Nova Scotia, data concerning the efficacy of eight interventional strategies used for controlling hypertension. These strategies were as follows: alcohol restriction, weight reduction, physical exercise, reduction of salt intake, relaxation/stress management, increase of potassium and calcium intake and combination of pharmacological and non-pharmacological management. The Panel of the Consensus Conference recommended as efficacious the following interventions: alcohol restriction for less than two standard drinks per day, reduction of excessive body weight, and reduction of salt intake. There is sufficient scientific evidence for recommending potassium rich diet for normotensives and hypertensive persons. The Panel also concluded that a combination of pharmacological and non-pharmacological management is an efficacious measure. The Panel at this point of time could not issue recommendations as to the value of relaxation/stress management, physical exercise and calcium intake.

[Preeclampsia: physiopathology and prospects for early detection]

Preeclampsia is a complication of pregnancy characterized by hypertension, edema and proteinuria, beginning after 20 weeks of gestation. Six percent of the pregnant women in North America develop this disease, which is associated with increased morbidity and mortality for the mother and her baby. The physiopathology remains uncertain despite many research efforts. Actual hypotheses seek to explain the vasospasm that characterizes the disease. Among the many factors influencing vascular reactivity and possibly implicated are: the renin-angiotensin system, prostaglandins, progesterone and its metabolites, calcium, magnesium, digoxin-like immunoreactive substance(s), auricular natriuretic factor, substances secreted by platelets and leukotrienes. Prevention of the disease is limited by the absence of a biological or clinical marker with good sensitivity and appropriate specificity. Many biochemical or hematological parameters have been reported: uric acid, calcium, magnesium, proteinuria, blood iron, hematocrit, platelet count, antithrombin III, estrogen and progesterone. The combination of several tests could be superior to the use of each test individually, providing a better sensitivity and improving the positive predictive value. With early detection, new therapies for the prevention of the disease could be experimented on the higher risk women before the apparition of clinical symptoms or signs. Furthermore, those tests could be used in the study of the pathophysiology and in the choice of the best therapy.

Possible involvement of atrial natriuretic factor in the antihypertensive action of a high-calcium diet in spontaneously hypertensive and Wistar-Kyoto rats

The present study was designed to determine the possible involvement of atrial natriuretic factor (ANF) in the hypotensive action of a high-calcium diet. The effects of increased dietary calcium (2.9% calcium, HCa) on blood pressure, urinary sodium excretion, and ANF were examined in 30 spontaneously hypertensive rats (SHR) and 30 Wistar-Kyoto rats (WKY). Control groups of 30 SHR and 30 WKY were fed normal calcium lab chow (0.4% calcium, NCa). The HCa diet reduced blood pressure and serum phosphorus concentration and increased urinary excretion of sodium and calcium in SHR and WKY. The HCa diet also caused a sustained increase in plasma ANF concentration and, finally, a decrease in atrial ANF concentration in both groups. A significant inverse correlation was observed between ANF concentrations in plasma and atria of the four experimental groups. Plasma ANF concentration was positively correlated with daily calcium consumption, and blood pressure was inversely correlated with daily calcium consumption in HCa- and NCa-SHR groups and in HCa- and NCa-WKY groups, respectively. Furthermore, a significant inverse correlation between blood pressure and plasma ANF concentration was observed in SHR groups and in WKY groups, respectively. The observed sustained increment in endogenous plasma ANF concentration, which is probably caused by increased secretion from the atrium, may contribute, in part, to the blood-pressure-lowering effects of the HCa diet.

Effect of calcium carbonate on blood pressure in normotensive and hypertensive people

Forty-seven patients with mild hypertension and 48 normotensive patients entered a blinded, parallel study in which they received a placebo, 10 mmol/day calcium carbonate (CaCO3), or 20 mmol/day CaCO3. There were no significant differences in blood pressure changes among the groups. In the hypertensive group and in patients with the highest blood pressure there were individual falls in systolic pressure, particularly in the group receiving 10 mmol daily CaCO3. In the hypertensive group the changes were: with placebo, -3 +/- 2/-2 +/- 2 mm Hg; with CaCO3 (10 mmol), -7 +/- 3/-2 +/- 2 mm Hg; and with CaCO3 (20 mmol), -2 +/- 3/1 +/- 2 mm Hg. No change was significant, and no pressure changes of patients taking CaCO3 differed significantly from changes of patients taking placebo. Ten of 33 patients taking placebo, 11 of 31 taking 10 mmol/day CaCO3, and nine of 31 taking 20 mmol/day CaCO3 were classified as responders from their systolic blood pressure fall. These response rates did not differ. Eight patients had falls of systolic blood pressure greater than 15 mm Hg. Five were on 10 mmol/day CaCO3 and three on 20 mmol/day CaCO3. This response was significantly different from that with placebo. Univariate analyses failed to reveal any predictive dietary or biochemical parameter. After 3 months of not taking CaCO3, 12 patients classified as responders, including six of the eight with a fall of 15 mm Hg or more, were rerandomized to placebo or to 20 mmol/day CaCO3. In the rechallenge, responses to CaCO3 and placebo were similar, neither causing a significant pressure fall. Calcium carbonate did not reduce blood pressure. The apparent response in a few patients was not verified by rechallenge. The present study does not support calcium supplementation as a useful nonpharmacological measure for reducing elevated blood pressure.

Effect of oral calcium on blood pressure response in salt-loaded borderline hypertensive patients

To clarify the mechanism of the antihypertensive effect of oral calcium loading, we studied the effect of low versus high calcium intake on salt-induced blood pressure elevations in patients with borderline hypertension. After a 7-day period of dietary salt restriction (50 meq/day), 27 patients were placed on a high salt (300 meq/day), low calcium (250 mg/day) diet for 7 days; 14 of these patients were given 2,160 mg/day of supplementary calcium (Ca group), and 13 patients were given placebo (non-Ca group). With a high salt intake, the percent increase in mean blood pressure was smaller in the Ca group than in the non-Ca group (+2.85 +/- 1.22% vs. +8.63 +/- 1.66%, respectively, p less than 0.01). The Ca group showed a smaller weight gain (p less than 0.05) and a greater urinary excretion of sodium (p less than 0.005) than the non-Ca group. In the Ca group, but not in the non-Ca group, high salt intake resulted in an increase in intraerythrocyte magnesium content (p less than 0.01), which was correlated inversely with the salt-induced changes in mean blood pressure (r = -0.54, p less than 0.05). While the increase in cellular magnesium was greater in the Ca group, the changes in red blood cell sodium and sodium/potassium ratio were not different between the two groups. The results suggest that oral calcium supplementation may prevent a rise in blood pressure in patients on a high salt, low calcium diet by attenuating the sodium retention.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic hypertension in diabetes mellitus

Hypertension occurs more frequently in diabetics and markedly exacerbates the vascular morbidity and mortality resulting from this metabolic disorder. However, the etiology of hypertension in diabetics remains poorly understood. Like aging persons, diabetics have increased systemic resistance and a probable reduction in baroreceptor sensitivity. They also have an expanded total body sodium pool and a tendency to lower levels of plasma renin activity. Some of these factors suggest that a subtle calcium deficiency could also be of etiologic importance.

Salt sensitivity and systemic hypertension in the elderly

Aging in industrialized societies is accompanied by increases in the incidence and prevalence of hypertension, with a disproportionately greater increase occurring among aging blacks than among aging whites. This geriatric hypertension is generally of a salt-sensitive nature with a disproportionate frequency of isolated systolic hypertension. Although salt-taste acuity declines with age, salt sensitivity among the elderly does not appear to result from a compensatory increase in salt intake. Rather, age-related increases in salt sensitivity result, in part, from a reduced ability to appropriately excrete a salt load, which is due to a decline in renal function and to a reduced generation of natriuretic substances such as prostaglandin E2 and dopamine. Age-associated declines in the activity of membrane sodium/potassium-adenosine triphosphatase (Na/K-ATPase) may also contribute to geriatric hypertension because this results in increased intracellular sodium that may cause reduced sodium-calcium exchange and thereby increase intracellular calcium and vascular resistance. Reductions in cellular calcium efflux due to reduced calcium-ATPase activity may similarly cause an increase in intracellular calcium and vascular resistance. Increasing dietary calcium intake may represent an effective nonpharmacologic treatment for some salt-sensitive persons because it appears to reduce intracellular calcium by (1) suppressing parathyroid hormone-mediated calcium influx, (2) increasing Na/K-ATPase activity, and (3) reducing intravascular volume due to calcium-induced natriuresis.

The relationship between calcium intake and pregnancy-induced hypertension: up-to-date evidence

In 1980 we pointed to a relationship between calcium intake and pregnancy-induced hypertension. The original epidemiologic observations showed an inverse association between calcium intake and incidence of eclampsia after adjusting by several confounding factors. A series of recent randomized clinical trials have demonstrated a reduction in blood pressure with calcium supplementation in animals, in healthy and mildly hypertensive subjects, and in pregnant women. It is hypothesized that parathyroid hormone plays a role since it is affected by calcium intake and can partially regulate the concentration of free cytosolic ionized calcium, thus triggering smooth muscle contraction. Randomized clinical trials showing a reduction in the incidence of pregnancy-induced hypertension with calcium supplementation have not as yet been published. However, preliminary observations appear to support this hypothesis.

Effect of marginal calcium intake on blood pressure in the Wistar rat

Epidemiological studies in man suggest that blood pressures tend to be higher in persons with low calcium (Ca) intakes. Previous studies in normal rats have shown that severe Ca restriction raises blood pressure. The chronic effect of moderate Ca restriction is not known. We evaluated the effect upon systolic blood pressure of rearing young Wistar rats on a diet marginally adequate in Ca. Male weanling Wistar rats (8 rats per group) were placed on one of four diets containing 0.5% Ca (control diet), 0.4% Ca, 0.3% Ca, or 0.2% Ca. The three experimental diets were made up by replacing CaHPO4 in the salt mix with (NH4)H2PO4. Content of PO4 and electrolytes other than Ca was the same for all 4 diets. Sodium (Na) content was 0.1%. Diets were fed for 19 weeks. Rats did not grow normally on the 0.2% Ca diet, but growth was normal on the other three diets. There was no overall statistically significant effect of diet upon systolic pressure. During the first nine weeks of study there were no significant differences between groups and no consistent trends. During the last seven weeks, however, there was a consistent trend toward higher systolic pressures as Ca intake decreased. The mean change in blood pressure during the last five weeks of study from the baseline value at 4 weeks of age was significantly greater in rats consuming 0.2% Ca and tended to be greater in rats consuming 0.3 and 0.4% Ca than in controls. On several occasions, group mean systolic pressures were significantly greater in rats on the experimental diets than in controls. Systolic pressures for individual rats, averaged over the last seven blood pressure measurements, varied over a wider range in the experimental groups than in rats eating the control diet, and the distribution in the experimental groups was shifted toward higher systolic pressures. The results suggest that rearing normal rats on a diet marginally adequate in Ca may lead to a modest elevation in the blood pressures of some, but not all rats. The effect, however, is of much smaller magnitude than that observed with severe Ca restriction.

Cations and hypertension: sodium, potassium, calcium, and magnesium

The association between sodium intake and hypertension has been studied for almost a century. More recently, it has been suggested that abnormalities in dietary intake of potassium, calcium, and magnesium may play a major role in the pathogenesis of hypertension. A critical analysis of selected data from animal and human studies is discussed.