Effect of calcium supplementation on pregnancy-induced hypertension and preeclampsia: a meta-analysis of randomized controlled trials

Dietary intakes of selected elements from longitudinal 6-day duplicate diets for pregnant and nonpregnant subjects and elemental concentrations of breast milk and infant formula

As part of a longitudinal investigation into mobilization of lead from the maternal skeleton during pregnancy and lactation, we have determined the daily intake of selected elements (hereafter called micronutrients) for various subjects and compared these intakes with recommended and/or published intakes, especially those of the United States, through the U.S. National Health and Nutrition Examination Survey (NHANES). We also sought to ascertain whether there was any seasonal effect in the diets. Six-day duplicate diets were collected from 15 pregnant and 16 nonpregnant migrants to Australia, 6 pregnant Australian control subjects, and 8 children of nonpregnant migrants (6 to 11 years). Samples of breast milk and infant formula were also analyzed. Blended samples were analyzed by inductively coupled plasma mass spectrometry for the elements Ca, Cu, Fe, Mg, P, K, Na, Zn, Ba, Sr, and Pb. Daily intakes of micronutrients were only about half of the daily intake estimated for non-Hispanic white females and infants in the U.S. NHANES III. Estimates of daily intakes from breast milk were also considerably lower for the migrant and Australian infants compared with the values extracted from tables of food composition and dietary recall for non-Hispanic white infants in the U.S. NHANES III. For example, Ca was a factor of approximately 3 times lower, Fe approximately 50, and Zn approximately 4. We consider our estimates a reliable indication of the daily intakes for several reasons, including the collection of up to nine quarterly collections of 6-day duplicate diets and retention of subjects in a longitudinal prospective study. The low intakes of the essential elements such as Ca, Fe, and Zn in all these population groups are of potential concern from a public health viewpoint.

Calcium modulation of hypertension and obesity: mechanisms and implications

Regulation of intracellular calcium plays a key role in hypertension and obesity. Dysregulation of calcium homeostasis appears to be a fundamental factor linking these conditions. Regulation of intracellular calcium in key disease-related target tissues by calcitrophic hormones provides the opportunity to modulate disease risk with dietary calcium. Overall, sub-optimal calcium intakes contribute to the etiology of salt-sensitivity and hypertension. High salt diets exert a calciuretic effect, serving to exacerbate the physiological consequences of sub-optimal calcium diets. Among these are increases in 1,25-dihydroxyvitamin D, which increases vascular smooth muscle intracellular calcium, thereby increasing peripheral vascular resistance and blood pressure. Dietary calcium reduces blood pressure in large part via suppression of 1,25-dihydroxyvitamin D, thereby normalizing intracellular calcium. The practical relevance of this approach has been confirmed in the DASH (Dietary Approaches to Stop Hypertension) trial, which demonstrated that increasing low-fat dairy product and fruit and vegetable consumption exerted profound blood pressure-lowering effects. The magnitude of this effect among hypertensives was comparable to that typically found in pharmacological trials of mild hypertension. 1,25-dihydroxyvitamin D also stimulates calcium influx in human adipocytes, resulting in stimulation of lipogenesis, inhibition of lipolysis and expansion of triglyceride stores. Accordingly, suppression of 1,25-dihydroxyvitamin D by dietary calcium has been identified as a target, which may contribute to the prevention and management of obesity. Indeed, laboratory, clinical and population data all indicate a significant anti-obesity effect of dietary calcium, although large-scale prospective clinical trials have not yet been conducted to definitively demonstrate the scope of this effect. Thus, available evidence indicates that increasing dietary calcium intakes may result in reductions in fat mass as well as in blood pressure.

Preeclampsia: from epidemiological observations to molecular mechanisms

Preeclampsia is the main cause of maternal mortality and is associated with a five-fold increase in perinatal mortality in developing countries. In spite of this, the etiology of preeclampsia is unknown. The present article analyzes the contradictory results of the use of calcium supplementation in the prevention of preeclampsia, and tries to give an explanation of these results. The proposal of an integrative model to explain the clinical manifestations of preeclampsia is discussed. In this proposal we suggest that preeclampsia is caused by nutritional, environmental and genetic factors that lead to the creation of an imbalance between the free radicals nitric oxide, superoxide and peroxynitrate in the vascular endothelium. The adequate interpretation of this model would allow us to understand that the best way of preventing preeclampsia is the establishment of an adequate prenatal control system involving adequate antioxidant vitamin and mineral supplementation, adequate diagnosis and early treatment of asymptomatic urinary and vaginal infections. The role of infection in the genesis of preeclampsia needs to be studied in depth because it may involve a fundamental change in the prevention and treatment of preeclampsia.

Supplementary calcium in prevention of pre-eclampsia

OBJECTIVE

To study the effect of calcium supplementation on reduction of pre-eclampsia in Iranian women at high risk of pre-eclampsia.

METHODS

Thirty pregnant women at high risk of developing pre-eclampsia were randomized to 2 g of daily calcium and placebo. Subjects and investigators were blinded to treatment allocation. The inclusion criteria were positive rollover test, having at least one risk factor for pre-eclampsia, between 28 and 32 weeks of pregnancy, and blood pressure less than 140/90 (mm Hg). Exclusion criteria were having any chronic condition. Pre-eclampsia was defined as systolic/diastolic blood pressure over 140/90 plus proteinuria. All the subjects were followed up to delivery.

RESULT

A sevenfold reduction in the occurrence of pre-eclamsia were seen among the calcium group compared with the placebo group (7 out of 15 developed pre-eclampsia in control group vs. 1 out of 15 in calcium group, P=0.014). No major effect on pregnancy induced hypertension was seen (66% in placebo and 76% in calcium group developed hypertension) but the onset of hypertension was delayed 3 weeks in the calcium group. A longer duration of pregnancy was seen in calcium than placebo (mean+/-S.D.=37+/-2 for calcium and 34+/-2 for placebo, P<0.05). Infants born to the calcium group, on average, were 552 g heavier than infants born to the placebo group, P<0.05.

CONCLUSION

Calcium supplementation is beneficial for preventing pre-eclampsia among Iranian women at high risk of developing pre-eclampsia.

Effects of a short-term vitamin D(3) and calcium supplementation on blood pressure and parathyroid hormone levels in elderly women

Calcium supplementation is effective in reducing blood pressure in various states of hypertension, including pregnancy-induced hypertension and preeclampsia. In addition, calcitropic hormones are associated with blood pressure. The hypothesis is that short-term therapy with calcium and vitamin D(3) may improve blood pressure as well as secondary hyperparathyroidism more effectively than calcium monotherapy. The effects of 8 weeks of supplementation with vitamin D(3) (cholecalciferol) and calcium on blood pressure and biochemical measures of bone metabolism were studied. The sample consisted of 148 women (mean +/- SD age, 74 +/- 1 yr) with a 25-hydroxycholecalciferol (25OHD(3)) level below 50 nmol/L. They received either 1200 mg calcium plus 800 IU vitamin D(3) or 1200 mg calcium/day. We measured intact PTH, 25OHD(3), 1,25-dihydroxyvitamin D(3), blood pressure, and heart rate before and after treatment. Compared with calcium, supplementation with vitamin D(3) and calcium resulted in an increase in serum 25OHD(3) of 72% (P < 0.01), a decrease in serum PTH of 17% (P = 0.04), a decrease in systolic blood pressure (SBP) of 9.3% (P = 0.02), and a decrease in heart rate of 5.4% (P = 0.02). Sixty subjects (81%) in the vitamin D(3) and calcium group compared with 35 (47%) subjects in the calcium group showed a decrease in SBP of 5 mm Hg or more (P = 0.04). No statistically significant difference was observed in the diastolic blood pressures of the calcium-treated and calcium- plus vitamin D(3)-treated groups (P = 0.10). Pearson coefficients of correlation between the change in PTH and the change in SBP were 0.49 (P < 0.01) for the vitamin D(3) plus calcium group and 0.23 (P < 0.01) for the calcium group. A short-term supplementation with vitamin D(3) and calcium is more effective in reducing SBP than calcium alone. Inadequate vitamin D(3) and calcium intake could play a contributory role in the pathogenesis and progression of hypertension and cardiovascular disease in elderly women.

Reliable assessment of the effects of treatment on mortality and major morbidity, I: clinical trials

This two-part review is intended principally for practising clinicians who want to know why some types of evidence about the effects of treatment on survival, and on other major aspects of chronic disease outcome, are much more reliable than others. Although there are a few striking examples of treatments for serious disease which really do work extremely well, most claims for big improvements turn out to be evanescent. Unrealistic expectations about the chances of discovering large treatment effects could misleadingly suggest that evidence from small randomised trials or from non-randomised studies will suffice. By contrast, the reliable assessment of any more moderate effects of treatment on major outcomes--which are usually all that can realistically be expected from most treatments for most common serious conditions--requires studies that guarantee both strict control of bias (which, in general, requires proper randomisation and appropriate analysis, with no unduly data-dependent emphasis on specific parts of the overall evidence) and strict control of random error (which, in general, requires large numbers of deaths or of some other relevant outcome). Past failures to produce such evidence, and to interpret it appropriately, have already led to many premature deaths and much unnecessary suffering.

Prevention of pre-eclampsia: status and perspectives 2000

Because pre-eclampsia is a relatively common complication of pregnancy and forms a major cause of maternal, fetal, and neonatal morbidity and mortality, attempts at prevention are justified, but hampered by the fact that as yet no reliable and acceptable screening tests for women at risk are available. Analysis of the many interventions advocated to prevent or delay the onset of pre-eclampsia reveals that dietary calcium supplementation and prophylactic low-dose aspirin treatment have shown promise of efficacy in small randomized, placebo-controlled trials, but the results of large, multicenter trials are generally disappointing. The disappointing results obtained in large, multicenter trials may in part be explained by the lack of strict criteria for inclusion, late initiation of treatment, use of ill-defined end points, different timing of aspirin ingestion, and low patient compliance. Recent evidence that supplementation with vitamins C and E could prevent pre-eclampsia awaits confirmation. Future clinical trials on prevention of pre-eclampsia should be based on results of basic research.

Calcium requirements of physically active people

Dietary calcium and physical activity have been independently, but inconsistently, associated with the development of increased peak bone mass and reduced bone loss later in life. An examination of the literature points to important effects of dietary calcium on bone health. During the development of peak bone mass, calcium intakes of <1 g/d are associated with lower bone mineral density. At intakes approaching calcium requirements, physical activity is a more important predictor of bone mineral density than is calcium intake. In studies of postmenopausal women, calcium intakes of 1 g (25 mmol/d) appear to be necessary to effect a positive impact of exercise on bone mineral density in the spine. Calcium intakes recommended for protecting bone health appear to be adequate to protect against other disorders with an etiology that includes inadequate dietary calcium. Calcium requirements as modified by physical activity need to be determined for each population subgroup according to sex, age, race, and cultural environment.

Role of nutrition in the prevention of toxemia

Toxemia of pregnancy is called the disease of theories because, over decades of research, numerous causes have been proposed but none proved. Although many nutritional factors have been suggested as playing a causal role in the etiology of toxemia, mortality from this disease has not varied over time or between circumstances as one would expect a nutritional disease to do. This does not mean that there is no nutritional influence, but it does mean that the available evidence does not show that nutrition makes a major difference in maternal mortality from toxemia of pregnancy.

Nutrition and maternal mortality in the developing world

This review relates nutritional status to pregnancy-related death in the developing world, where maternal mortality rates are typically >/=100-fold higher than rates in the industrialized countries. For 3 of the central causes of maternal mortality (ie, induced abortion, puerperal infection, and pregnancy-induced hypertension), knowledge of the contribution of nutrition is too scanty for programmatic application. Hemorrhage (including, for this discussion, anemia) and obstructed labor are different. The risk of death is greatly increased with severe anemia (Hb <70 or 80 g/L); there is little evidence of increased risk associated with mild or moderate anemia. Current programs of universal iron supplementation are unlikely to have much effect on severe anemia. There is an urgent need to reassess how to approach anemia control in pregnant women. Obstructed labor is far more common in short women. Unfortunately, nutritional strategies for increasing adult stature are nearly nonexistent: supplemental feeding appears to have little benefit after 3 y of age and could possibly be harmful at later ages, inducing accelerated growth before puberty, earlier menarche (and possible earlier marriage), and unchanged adult stature. Deprived girls without intervention typically have late menarche, extended periods of growth, and can achieve nearly complete catch-up growth. The need for operative delivery also increases with increased fetal size. Supplementary feeding could therefore increase the risk of obstructed labor. In the absence of accessible obstetric services, primiparous women <1.5 m in height should be excluded from supplementary feeding programs aimed at accelerating fetal growth. The knowledge base to model the risks and benefits of increased fetal size does not exist.

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.

Bioavailability of the calcium in fortified soy imitation milk, with some observations on method

BACKGROUND

Calcium-fortified soy milk is growing in popularity, particularly among vegetarians, but the bioavailability of its calcium was not previously known. Additionally, the validity of isotopic labeling methods for fortified liquid products had not been established.

OBJECTIVES

The objectives of this study were to compare the bioavailability of the calcium in fortified soy milk with that of calcium in cow milk and to evaluate the method of labeling soy milk for bioavailability testing.

DESIGN

A within-subject comparison of extrinsically labeled cow milk with intrinsically and extrinsically labeled soy milks was undertaken in 16 healthy men. In all tests, 300-mg Ca loads were given as a part of a light breakfast after an overnight fast. The milks were physically partitioned into liquid and solid phases to enable evaluation of tracer distribution.

RESULTS

Calcium from intrinsically labeled soy milk was absorbed at only 75% the efficiency of calcium from cow milk. Extrinsic labeling of soy milk did not produce uniform tracer distribution throughout the liquid and solid phases and resulted in a 50% overestimate of true absorbability.

CONCLUSION

Calcium-fortified soy milk does not constitute a calcium source comparable to cow milk, and extrinsic labeling of such calcium particulate suspensions does not produce the uniform tracer distribution needed for bioavailability testing. Hence, intrinsic labeling of the fortificant is required for such liquid suspensions.

A prospective management study of slow-release aspirin in the palliation of uteroplacental insufficiency predicted by uterine artery Doppler at 20 weeks

OBJECTIVE

To investigate the effect of low-dose, slow-release aspirin in reducing the incidence and/or severity of pregnancy complications in women identified as high risk of developing problems associated with uteroplacental insufficiency, namely pre-eclampsia or delivering a small-for-gestational age (SGA) baby.

DESIGN

A prospective, randomized management study. One thousand and twenty-two women of mixed parity underwent color flow/pulsed Doppler (CFPD) imaging of the uterine arteries at the time of the 17-23 week (mean 19.9) anomaly scan. Women who were screen positive were randomized to a control or treatment group. The treatment group was given 100-mg slow-release aspirin (Disprin CV) daily and followed up at regular intervals. Women in the routine group received routine antenatal care. Main outcome measures were pre-eclampsia and SGA < 3rd centile. Secondary outcome measures were: SGA < 10th centile, pre-eclampsia requiring delivery before 34 weeks, placental abruption, an Apgar score < 7 at 5 min, admission to neonatal intensive care unit or a pregnancy that resulted in a stillbirth or neonatal death. Odds ratios (OR) with 95% confidence intervals (CI) were calculated for severe and any complications.

RESULTS

Two hundred and sixteen women were screen positive according to the defined criteria. One hundred and three women were assigned to the treatment group and 113 to the control group. The difference in the incidence of pre-eclampsia and SGA < 3rd centile between the control and treatment groups did not reach statistical significance. There was a statistically significant reduction in any (OR 0.41 (CI 0.35-0.45), P < 0.01) and severe pregnancy complications (OR 0.43 (CI 0.21-0.84), P < 0.05) in the treatment group compared with the controls.

CONCLUSIONS

The administration of slow-release aspirin to women identified as high risk, using color Doppler imaging of the uterine arteries at 20 weeks' gestation, did not significantly alter the incidence of pre-eclampsia or delivery of a SGA baby. It did, however, improve the outcome by reducing the overall incidence of complications associated with uteroplacental insufficiency.

The role of calcium in health and disease

Skeletal fragility at the end of the life span (osteoporosis) is a major source of morbidity and mortality. Adequate calcium intake from childhood to the end of the life span is critical for the formation and retention of a healthy skeleton. High intakes of calcium and vitamin D potentiate the bone loss prevention effects of hormone replacement therapy in postmenopausal women. Pregnancy and lactation are not risk factors for skeletal fragility, although lactation is associated with a transient loss of bone that cannot be prevented by calcium supplementation. Low calcium intake has been implicated in the development of hypertension, colon cancer, and premenstrual syndrome, and it is associated with low intakes of many other nutrients. Encouragement of increased consumption of calcium-rich foods has the potential to be a cost-effective strategy for reducing fracture incidence later in life and for increasing patients' dietary quality and overall health.

Calciuria in symptom-free primigravid women remote from term: is the response to an oral calcium challenge predictable?

OBJECTIVE

This study was undertaken to compare the calciuric response in symptom-free primigravid women to an oral calcium load between those with normal urinary calcium excretions and those with relatively low urinary calcium excretions.

STUDY DESIGN

This was a prospective clinical trial. Eligible primigravid women between 16 and 20 weeks' gestation provided a 24-hour urine sample for determination of urinary calcium/urinary creatinine ratio. On the basis of these results the patients were divided into 2 groups: a relatively hypocalciuric group, in which the urinary calcium excretion was </=3.4 mg. kg-1. 24 h-1, and a normocalciuric group, in which the urinary calcium excretion was >3.4 mg. kg-1. 24 h-1. All participants undertook a 3-day low calcium dietary regimen. On the fourth day women underwent an oral calcium challenge. A 2-hour urine sample was collected before ingestion of 1 g calcium carbonate (preload). One hour after ingestion the women again collected a 2-hour urine sample (postload). The urinary calcium/urinary creatinine ratios in the preload and postload samples were determined and compared within and between the groups.

RESULTS

The mean change (+/-SD) between the preload and postload urinary calcium/urinary creatinine ratios in the relatively hypocalciuric group was 0.60 +/- 1.44 (P =.04); that in the normocalciuric group was 3.09 +/- 2.26 (P =.11 ). There was a 5-fold difference in the response to calcium load between the hypocalciuric women and the normocalciuric women (0.60 vs 3.09), although this difference was not statistically significant (P =.20).

CONCLUSIONS

Both hypocalciuric and normocalciuric women responded to an oral calcium challenge by an increase in the calcium excretion. The cause of the hypocalciuria in women at increased risk for preeclampsia is therefore not simply poor absorption of calcium.

Optimality of the birth population reduces learning and behaviour disorders and sudden infant death after the first month

The weight distribution pattern of all births can be divided into a "skewing to the left" to lower weights and high neonatal mortality, a "skewing to the right" to higher weights (>3500g) and minimum neonatal and postneonatal mortality, and a "symmetrical distribution" with mortality in between. This study was initiated with the hypothesis that a deficit in newborns of more than 3500 g would adversely affect postneonatal death. Higher and rising postneonatal mortality solely attributable to sudden infant death of unknown cause (sudden infant death syndrome; SIDS) was observed in the Nordic countries with a lower proportion of heavy newborns. Minor environmental intervention almost eliminated excess mortality from this cause, supporting raised susceptibility with a depressed birthweight in postneonatal SIDS. This contrasts with classical neonatal low birthweight SIDS, which is stable despite numerous attempts at reduction, supporting a multi-factorial aetiology: low maternal age, low education, low socioeconomic status, maternal smoking, infection, etc. The postneonatal SIDS epidemic associated with a deficit in heavy newborns is thought to be a result of changing behaviour in pregnancy: moderate iatrogenic dietary restriction and young women favouring a low-calorie, low-fat diet, especially in the third trimester when the foetus is most vulnerable, which delays myelination and somatic growth and renders the infant susceptible to minor morbidity and irregularity. The timing of death and neuropathological findings suggestive of repeated hypoxic episodes in more than 80% of cases of SIDS prior to death support this theory. The similar weight distribution patterns in SIDS and all births in Denmark, the UK and the USA suggest a substantial proportion of the neonates in these countries could be growth-retarded and at risk of hypoxic episodes in infancy. A few cases, particularly males (sex-ratio = 1.7), suffer SIDS, the majority survive. Many, mostly males, present minor CNS signs and learning and behaviour problems. The male predominance accords with males more than 500 g higher optimal birthweight than females and susceptibility to a depressed weight at birth. In order to prevent postneonatal dying, SIDS and reduce learning/behaviour disorders it is necessary to raise the proportion of heavy newborns by promoting foetal growth rate equal to the maternal intrinsic rate by eating to one's appetite a balanced diet, favouring a diet high in marine fat, especially in third trimester, in order to ensure maturation of the CNS and prolong gestation, thereby increasing birthweight. Although the increased survival of some very low birthweight neonates confounds the issue, a division between SIDS in neonatal and postneonatal death is recommended in order to assess the proportion of "avoidable infant death" as opposed to persistent classical neonatal SIDS.

Serum calcium and parathormone during normal pregnancy in Malay women

OBJECTIVE

To ascertain the calcium status in normal pregnant Malay women.

METHODS

In a cross-sectional study, serum parathormone (PTH) and calcium concentrations, and 24-h urinary calcium excretion were estimated in age-matched normotensive pregnant women, over the 3 trimesters.

RESULTS

No statistically significant differences were evident in serum ionised calcium concentrations between the pregnant women in the 3 trimesters. Serum total calcium however, was significantly lower in women in the 3rd trimester of pregnancy (2.29+/-0.16, 2.26+/-0.13, and 2.16+/-0.12 mmol l(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.001). Serum parathyroid hormone concentration was significantly higher in the 3rd trimester of pregnancy (3.37+/-3.31, 4.36+/-4.55, and 7.17+/-6.6 pg ml(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.05). No significant differences were evident in serum sodium and potassium concentrations between the 3 groups. Urinary calcium excretion was significantly lower in women in the 3rd trimester of pregnancy (3.41+/-1.80, 3.56+/-3.31, and 2.46+/-1.71 mmol day(-1) in the 1st, 2nd, and in the 3rd trimesters, respectively; P < 0.05). No significant differences were evident in urine output, creatinine clearance, or in the excretion of sodium and potassium between the 3 groups.

CONCLUSIONS

It appears that a significant fall in serum total calcium occurs in the 2nd half of normal human pregnancy when there is also an increased fetal demand and perhaps also a relatively insufficient maternal intake and/or intestinal absorption. The lower urinary calcium excretion probably occurs secondary to this and may suggest a fall in total body calcium and an attempt by the body to conserve calcium. While under normal circumstances, this level of fall in total calcium may not be significant, the coincidence of occurrence of hypertensive disorders of pregnancy during this stage of pregnancy, and the evident link between low calcium intake and pregnancy-induced hypertension (PIH) and its possible amelioration with calcium supplementation, suggests a need to assess calcium status in pregnant women with a view to providing calcium supplementation during pregnancy.

Calcium supplementation in nulliparous women for the prevention of pregnancy-induced hypertension, preeclampsia and preterm birth: an Australian randomized trial. FRACOG and the ACT Study Group

A multicentre, randomized controlled double-blind trial in 5 maternity hospitals in Australia assessed the effect of a daily supplement of calcium (1.8g oral calcium or an oral placebo) taken daily until delivery, from less than 24 weeks' gestation, on the frequency of pregnancy-induced hypertension, preeclampsia and preterm birth (< 37 weeks' gestation) in 456 nulliparas with a singleton pregnancy. Treatment with calcium reduced the risk of preeclampsia (relative risk 0.44 [95% CI, 0.21-0.90], p = 0.02) and the risk of preterm birth (relative risk 0.44 [95% CI, 0.21-0.90], p = 0.02). No significant differences were seen between the 2 groups in the frequency of pregnancy-induced hypertension, although the study only had statistical power to detect large differences in this outcome. An updated systematic review of the 9 randomized trials of calcium supplementation in pregnancy shows a significant reduction in the risk of hypertension and preeclampsia although no effect on preterm birth. Calcium supplementation during pregnancy reduced the risk of preeclampsia and preterm birth in this nulliparous population. The available evidence for systematic review of all the randomized trials of calcium supplementation shows benefit in reducing the risk of hypertension and preeclampsia.

Dietary calcium and mineral/vitamin supplementation: a controversial problem

There is a consensus that adequate calcium intake during bone development, and possibly in adulthood and senescence, helps to prevent bone resorption and osteoporosis. The uptake of dietary calcium should be sufficient to maintain both normal serum calcium concentrations and parathyroid hormone levels in the low normal range throughout the day, otherwise, increased bone resorption occurs. Calcium intake varies with race and with environmental and dietary conditions. Estimating the appropriate amount of calcium to be added to dietary sources for an optimal supplementation regimen is therefore difficult. Few intervention studies have evaluated the dose-effect relationship for calcium supplementation conclusively. The mechanisms regulating fractional calcium absorption as a function of intake suggest that very high daily doses are probably useless. They may be unsafe in the long term because of the risks of hypercalciuria and kidney stones, and of an imbalance in the ratio of calcium to magnesium. Concomitant supplementation with limited amounts of magnesium may reduce this risk and improve mineralization. Dietary intake is 500-600 mg/day in most studies, making 400 mg/day an appropriate supplementary dose for most premenopausal women (RDA 1000 mg/day). After the menopause and during lactation (RDA 1200-1500 mg/day), 800 mg/day is probably appropriate, particularly if low doses of vitamin D are taken concomitantly.

Nutritional interventions for the prevention of maternal morbidity

OBJECTIVE

To review the effectiveness of nutritional interventions to prevent maternal morbidity.

METHODS

This is an overview of systematic reviews and individual randomized controlled trials (if no systematic review available) of nutritional interventions during pregnancy. For each nutrient intervention the main maternal morbidity data reported were extracted. These were pre-eclampsia/eclampsia, pregnancy-induced hypertension, hemorrhage, anemia, infection and obstructed labor. In addition, the trial settings, the number of trials and participants' characteristics were systematically extracted.

RESULTS

The systematic reviews considered in this paper had only few trials that reported the selected maternal outcomes. Outcome measures are based sometimes on one trial only. Most of the interventions compared single micronutrient supplementation with placebo/no treatment and did not show significant benefits for the supplementation groups. Calcium supplementation in women at high risk of pregnancy hypertension reduced the incidence of high blood pressure (RR, 0.35; 95% CI, 0.21-0.57) and pre-eclampsia (RR, 0.22; 95% CI, 0.11-0.43). Similarly, in women with low dietary calcium intake, calcium supplementation resulted in a significant reduction in the incidence of high blood pressure (RR, 0.49; 95% CI, 0.38-0.62) and pre-eclampsia (RR, 0.32; CI, 0.21-0.49). In women at low risk of pregnancy hypertension or with adequate baseline calcium intake, the beneficial effects of calcium supplementation are small and unlikely to be of clinical significance. Both, iron and folate supplementation reduced the number of women with low pre-delivery hemoglobin.

CONCLUSIONS

Routine calcium supplementation seems to be a promising intervention for pregnant women at risk of developing preeclampsia or have low calcium intake, but these findings need to be confirmed with a trial with adequate power in different settings. In populations with high incidence of nutritional anemia routine iron and folate supplementation should be recommended during ante-natal care. It is unclear at this stage if adding vitamin A to iron and folate supplementation in anemia prevalent areas provides further benefits. There is inadequate data on the benefits or harms of routine iron or folate supplementation in adequately nourished populations. With regard to other micronutrient supplementation, such as zinc, magnesium and fish oil, randomized controlled trials with sufficient power to detect clinically important differences in maternal and infant outcomes are needed.

Urinary calcium/creatinine ratio as a predictor of preeclampsia

Hypocalciuria has been associated with preeclampsia (gestational hypertension with proteinuria or other maternal organ dysfunction) but not usually with pure gestational hypertension or normal pregnancy. We hypothesized that hypocalciuria would be a marker of emerging preeclampsia in women presenting with gestational hypertension who later developed preeclampsia. Eighty-one women with de novo hypertension in the second half of pregnancy (n = 81) were enrolled prospectively. At first assessment, calcium/creatinine ratio was determined in a spot urine. Patients were followed until delivery and were classified subsequently according to the occurrence of preeclampsia. Gestational hypertensive patients who became preeclamptic (n = 31) had lower urinary calcium/creatinine ratios at presentation (ratio = 0.07, interquartile range [IQR] = 0.04-0.11) than women who remained as gestational hypertensives (n = 50; ratio = 0.17, IQR = 0.08-0.21; P = .002). Intact plasma parathyroid hormone (PTH) concentrations were similar between groups. Using a receiver operator curve, the best threshold value for the development of preeclampsia was a calcium/creatinine ratio of 0.10, which yielded a sensitivity of only 68% and a specificity of 70%. A low calcium/creatinine ratio preceded the emergence of preeclampsia by 12 (7-24) (median [IQR]) days among a group of women with gestational hypertension. Though this implies primary or secondary disturbances of renal calcium handling even before preeclampsia is clinically apparent, this measurement does not have sufficient sensitivity to recommend its use as a screening test for the emergence of preeclampsia.

The prevention and management of pre-eclampsia and eclampsia

Pre-eclampsia and eclampsia remain one of the leading causes of maternal morbidity and mortality worldwide. They also contribute to perinatal morbidity and mortality as well. Multiple strategies have been proposed for the prevention of pre-eclampsia, with mixed results. Likewise, different strategies for the management of pre-eclampsia have been proposed, also with mixed results. While the prevention of pre-eclampsia remains unachievable, meticulous medical management of mother and fetus will contribute to an overall lowering of pre-eclampsia and eclampsia's contribution to perinatal and maternal morbidity and mortality.

Dietary factors in the pathogenesis and treatment of hypertension

Data accumulated from epidemiological observations, intervention trials and studies on experimental animals provide a growing body of evidence of the influence of various dietary components on blood pressure. Dietary sodium, usually taken in the form of sodium chloride (common salt), is positively associated with blood pressure, and in many hypertensive patients reduction in sodium intake lowers blood pressure. On the other hand, in certain patients potassium, calcium and magnesium may be protective electrolytes against hypertension. Dietary fats, especially n-3 polyunsaturated fatty acids, may also influence blood pressure, whereas the possible role of other macronutrients, such as proteins and carbohydrates, or vitamins in the regulation of blood pressure is less well understood. Occasional ingestion of coffee transiently increases blood pressure, but the effects of habitual coffee consumption are controversial. Excessive use of alcohol on a regular basis has been associated with elevated blood pressure. It has also been shown in case reports that large amounts of liquorice lead to the development of hypertension. Thus, with appropriate dietary modifications, it is possible to prevent the development of high blood pressure and to treat hypertensive patients with fewer drugs and with lower doses. In some patients antihypertensive medication may not be at all necessary.

Hypertension and pregnancy-related hypertension

Pregnant women with hypertension can be divided into two groups: normotensive women who develop the uniquely pregnancy-related syndrome of preeclampsia, which is characterized by hypertension, proteinuria, and edema; and women with chronic hypertension who become pregnant and are at increased risk for developing superimposed preeclampsia. Preeclampsia is a syndrome of generalized endothelial dysfunction initiated by abnormal placentation and consequent placental under-perfusion, release of cytokines and other toxins, and vasoconstriction and platelet activation. Preeclampsia is the major cause of both maternal and fetal morbidity and mortality and may be complicated by eclampsia (seizures) and hepatic and renal failure. The process is completely reversible by delivery of the fetus and placenta, but intrauterine growth retardation and premature delivery pose major threats to the fetus and may require care in tertiary care center. Treatment of preexisting or pregnancy-induced hypertension does not prevent or reverse the process, but is justified to prevent maternal cardiovascular complications, especially during labor and delivery.

Summing up evidence: one answer is not always enough

Are meta-analyses the brave new world, or are the critics of such combined analyses right to say that the biases inherent in clinical trials make them uncombinable? Negative trials are often unreported, and hence can be missed by meta-analysts. And how much heterogeneity between trials is acceptable? A recent major criticism is that large randomised trials do not always agree with a prior meta-analysis. Neither individual trials nor meta-analyses, reporting as they do on population effects, tell how to treat the individual patient. Here we take a more rounded approach to meta-analyses, arguing that their strengths outweigh their weaknesses, although the latter must not be brushed aside.

Perivascular sensory nerve Ca2+ receptor and Ca2+-induced relaxation of isolated arteries

The present study tested two hypotheses: (1) that a receptor for extracellular Ca2+ (Ca2+ receptor [CaR]) is located in the perivascular sensory nerve system and (2) that activation of this receptor by physiological concentrations of extracellular Ca2+ results in the release of vasodilator substance that mediates Ca2+-induced relaxation. Reverse transcription-polymerase chain reaction using primers derived from rat kidney CaR cDNA sequence showed that mRNA encoding a CaR is present in dorsal root ganglia but not the mesenteric resistance artery. Western blot analysis using monoclonal anti-CaR showed that a 140-kD protein that comigrates with the parathyroid CaR is present in both the dorsal root ganglia and intact mesenteric resistance artery. Immunocytochemical analysis of whole mount preparations of mesenteric resistance arteries showed that the anti-CaR-stained perivascular nerves restricted to the adventitial layer. Biophysical analysis of mesenteric resistance arteries showed that cumulatively raising Ca2+ from 1 to 1.25 mol/L and above relaxes precontracted arteries with an ED50 value of 2.47+/-0.17 mmol/L (n=12). The relaxation is endothelium independent and is unaffected by blockade of nitric oxide synthase but is completely antagonized by acute and subacute phenolic destruction of perivascular nerves. A bioassay showed further that superfusion of Ca2+ across the adventitial surface of resistance arteries releases a diffusible vasodilator substance. Pharmacological analysis indicates that the relaxing substance is not a common sensory nerve peptide transmitter but is a phospholipase A2/cytochrome P450-derived hyperpolarizing factor that we have classified as nerve-derived hyperpolarizing factor. These data demonstrate that a CaR is expressed in the perivascular nerve network, show that raising Ca2+ from 1 to 1.25 mol/L and above causes nerve-dependent relaxation of resistance arteries, and suggest that activation of the CaR induces the release of a diffusible hyperpolarizing vasodilator. We propose that this system could serve as a molecular link between whole-animal Ca2+ balance and arterial tone.

Diet and nutrition in primary care. From antioxidants to zinc

This article reviews the role of diet in primary prevention based on current epidemiologic and clinical studies. Special consideration is given to circumstances which may require individualizing the dietary prescription. The role of dietary supplements in primary care is discussed. Particular emphasis is given to studies highlighting the clinical importance of specific minerals. Additionally, the practical application of antioxidant vitamins is presented in light of recent research findings.

Effects of elements on blood pressure

This article present a comprehensive review of all known elements involved in blood pressure control. Data source was by computerized literature searches. A total of 28 elements have been documented as being involved in blood pressure control. The individual elements react directly and indirectly in a variety of metabolic and structural activities known to participate in blood pressure regulation. Reports from both experimental animal and human subjects are presented. The role of certain elements in blood pressure control is controversial. Conversely, important established functions of dosage, absorption, storage, and excretion of individual elements are known and are described in relation to blood pressure control. Some elements are pressor, whereas others are depressor in action, and this article demonstrates the important role elements play in the control of blood pressure.