The effect of calcium consumption on iron absorption and iron status

Calcium supplementation for people with overweight or obesity

BACKGROUND

Obesity is a major health problem worldwide as it can lead to high blood pressure, heart disease, stroke, diabetes, and insulin resistance. The prevalence of overweight and obesity is increasing worldwide across different age groups. There is evidence of an inverse relationship between calcium intake and body weight. The clinical relevance of a small reduction in body weight has been questioned. However, at a population level, a small effect could mitigate the observed global trends.

OBJECTIVES

To assess the effects of calcium supplementation on weight loss in individuals living with overweight or obesity.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, LILACS (Latin American and Caribbean Health Science Information database), and two clinical trials registries. The date of the last search of all databases (except Embase) was 10 May 2023. No language restrictions were applied.

SELECTION CRITERIA

We included randomised controlled trials evaluating the effect of calcium in participants with overweight or obesity of any age or gender. We excluded studies in participants with absorption problems. We included studies of any dose with a minimum duration of two months. We included the following comparisons: calcium supplementation versus placebo, calcium-fortified food or beverage versus placebo, or calcium-fortified food or beverage versus non-calcium-fortified food or beverage. We excluded studies that evaluated the effect of calcium and vitamin D or mixed minerals compared to placebo.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Our primary outcomes were body weight, health-related quality of life, and adverse events. Our secondary outcomes were anthropometric measures other than body weight, all-cause mortality, and morbidity.

MAIN RESULTS

We found 18 studies that evaluated the effect of calcium compared to placebo or control, with a total of 1873 randomised participants (950 participants in the calcium supplementation groups and 923 in the control groups). All included studies gave oral calcium supplementation as the intervention. We did not find any studies evaluating calcium-fortified foods. We excluded 38 studies, identified four ongoing studies, and listed one study as 'awaiting classification'. Sixteen studies compared calcium supplementation to placebo; two studies compared different doses of calcium supplementation. Doses ranged from very low (0.162 g of calcium/day) to high (1.5 g of calcium/day). Most studies were performed in the USA and Iran, lasted less than six months, and included only women. Low-certainty evidence suggests that calcium supplementation compared to placebo or control may result in little to no difference in body weight (mean difference (MD) -0.15 kg, 95% confidence interval (CI) -0.55 to 0.24; P = 0.45, I2 = 46%; 17 studies, 1317 participants; low-certainty evidence). We downgraded the certainty of the evidence by two levels for risk of bias and heterogeneity. None of the included studies reported health-related quality of life, all-cause mortality, or morbidity/complications as outcomes. Only five studies assessed or reported adverse events. Low-certainty evidence suggests a low frequency of adverse events, with no clear difference between intervention and control groups. Moderate-certainty evidence shows that calcium supplementation compared to placebo or control probably results in a small reduction in body mass index (BMI) (MD -0.18 kg/m2,95% CI -0.22 to -0.13; P < 0.001, I2 = 0%; 9 studies, 731 participants) and waist circumference (MD -0.51 cm, 95% CI -0.72 to -0.29; P < 0.001, I2 = 0%; 6 studies, 273 participants). Low-certainty evidence suggests that calcium supplementation compared to placebo or control may result in a small reduction in body fat mass (MD -0.34 kg, 95% CI -0.73 to 0.05; P < 0.001, I2 = 97%; 12 studies, 812 participants).

AUTHORS' CONCLUSIONS

Calcium supplementation for eight weeks to 24 months may result in little to no difference in body weight in people with overweight or obesity. The current evidence is of low certainty, due to concerns regarding risk of bias and statistical heterogeneity. We found that the degree of heterogeneity might be partly explained by calcium dosage, the presence or absence of a co-intervention, and whether an intention-to-treat analysis was pursued. While our analyses suggest that calcium supplementation may result in a small reduction in BMI, waist circumference, and fat mass, this evidence is of low to moderate certainty. Future studies could investigate the effect of calcium supplementation on lean body mass to explore if there is a change in body composition.

Current iron therapy in the light of regulation, intestinal microbiome, and toxicity: are we prescribing too much iron?

Iron deficiency is a widespread global health concern with varying prevalence rates across different regions. In developing countries, scarcity of food and chronic infections contribute to iron deficiency, while in industrialized nations, reduced food intake and dietary preferences affect iron status. Other causes that can lead to iron deficiency are conditions and diseases that result in reduced intestinal iron absorption and blood loss. In addition, iron absorption and its bioavailability are influenced by the composition of the diet. Individuals with increased iron needs, including infants, adolescents, and athletes, are particularly vulnerable to deficiency. Severe iron deficiency can lead to anemia with performance intolerance or shortness of breath. In addition, even without anemia, iron deficiency leads to mental and physical fatigue, which points to the fundamental biological importance of iron, especially in mitochondrial function and the respiratory chain. Standard oral iron supplementation often results in gastrointestinal side effects and poor compliance. Low-dose iron therapy seems to be a valid and reasonable therapeutic option due to reduced hepatic hepcidin formation, facilitating efficient iron resorption, replenishment of iron storage, and causing significantly fewer side effects. Elevated iron levels influence gut microbiota composition, favoring pathogenic bacteria and potentially disrupting metabolic and immune functions. Protective bacteria, such as bifidobacteria and lactobacilli, are particularly susceptible to increased iron levels. Dysbiosis resulting from iron supplementation may contribute to gastrointestinal disorders, inflammatory bowel disease, and metabolic disturbances. Furthermore, gut microbiota alterations have been linked to mental health issues. Future iron therapy should consider low-dose supplementation to mitigate adverse effects and the impact on the gut microbiome. A comprehensive understanding of the interplay between iron intake, gut microbiota, and human health is crucial for optimizing therapeutic approaches and minimizing potential risks associated with iron supplementation.

In vitro evaluation of the effect of yogurt acid whey fractions on iron bioavailability

A side effect of the raised consumption of Greek yogurt is the generation of massive amounts of yogurt acid whey (YAW). The dairy industry has tried several methods for handling these quantities, which constitute an environmental problem. Although the protein content of YAW is relatively low, given the huge amounts of produced YAW, the final protein amount in the produced YAW should not be underestimated. Taking into consideration the increased interest for bioactive peptides and the increased demand for dietary proteins, combined with protein and peptides content of YAW, efforts should be made toward reintroducing the latter in the food supply chain. In this context and in view of the prevalent dietary iron deficiency problem, the objective of the present study was the investigation of YAW fractions' effect on Fe bioavailability. With this purpose, an in vitro digest approach, following the INFOGEST protocol, was coupled with the Caco2 cell model. To evaluate whether YAW digest fractions exert positive, negative or neutral effect on Fe bioavailability, they were compared with the ones derived from milk, a well-studied food in this context. Milk and YAW showed the same effectiveness on both Fe bioavailability and the expression of relative genes (DCYTB, DMT1, FPN1, and HEPH). Focusing further on YAW fractions, by comparison with their blank digest control counterparts, it resulted that YAW 3- to 10-kDa digests fraction had a superior effect over the 0- to 3-kDa fraction on Fe-uptake, which was accompanied by a similar effect on the expression of Fe metabolism-related genes (DCYTB, FPN1, and HEPH). Finally, although the 3- to 10-kDa fraction of bovine YAW digests resulted in a nonsignificant increased Fe uptake, compared with the ovine and caprine YAW, the expression of DCYTB and FPN1 genes underlined this difference by showing a similar pattern with statistically significant higher expression of bovine compared with ovine and bovine compared with both ovine and caprine, respectively. The present study deals with the novel concept that YAW may contain factors affecting Fe bioavailability. The results show that it does not exert any negative effect and support the extensive investigation for specific peptides with positive effect as well as that YAW proteins should be further assessed on the prospect that they can be used in human nutrition.

Calcium-Deficit Diet Improves Iron Content in Ovariectomized Rats

In women, menopause is associated with disorders related to calcium and iron content, which may increase the risk of osteoporosis. This study aimed to determine the effect of calcium deficiency on the iron content in ovariectomized rats. This study included 30 3-month-old female rats, which were divided into three groups: group C (n = 10)-control group fed the standard diet; group O-ovariectomized rats fed the standard diet; and group D-ovariectomized rats fed the calcium-deficit diet. After 3 months of experimental intervention, the weight of the rats was measured, and blood and tissue samples were collected. Morphological parameters were analyzed in whole blood, and serum levels of leptin, estrogen and C-reactive protein, and total antioxidant status were determined. The iron content was measured in tissues, and histological analysis was performed in the femur. The results obtained demonstrated that ovariectomy significantly decreased the iron content in bones, hair, spleen, liver, and kidneys. The calcium-deficit diet increased the iron content in tissues and the hemoglobin level in ovariectomized rats and also enhanced the number of osteoblasts in bones compared with the O group. In conclusion, calcium deficiency improved the iron content in ovariectomized rats in this 12-week study.

Patterns of 25-Hydroxyvitamin D3, Calcium Status, and Anemia in the Saudi Population: A Cross-Sectional Study

BACKGROUND

Emerging evidence suggests an intricate relationship between vitamin D, Ca²⁺, and inflammation-driven anemia. We, thus, investigated the patterns of serum 25(OH)D₃, Ca²⁺, ferritin, and iron in healthy and anemic members of the Saudi population.

METHODS

A population-based, retrospective, cross-sectional study was designed to analyze data for 14,229 subjects, aged 3-110 years, obtained from Al-Borg Medical Laboratories, over a six-year period (2014-2020). Gender and age differences were analyzed for 25(OH)D₃, Ca²⁺, hemoglobin, ferritin, and iron.

RESULTS

Vitamin D deficiency was extremely prevalent (98.47%) irrespective of age or gender, despite an increasing trend with age, in clear contrast to serum Ca²⁺. Ferritin was significantly lower in young adult and adult females, compared to elderly females, whereas iron was significantly reduced in females; in particular, adult females compared to young adults or elderly adults. Only anemic adult males had significantly lower 25(OH)D₃, while Ca²⁺ was consistently significantly diminished in anemics of all age groups, independent of gender. Notably, hypocalcemic subjects were 2.36 times more likely to be anemic. Moreover, ferritin, but not iron, was significantly diminished in anemics, which was only evident in young adults and adults. However, both ferritin and iron showed positive correlation with hematocrit, hemoglobin, MCH, MCHC, and MCV.

CONCLUSIONS

Despite being significantly lower in anemics, 25(OH)D₃ is not particularly associated with anemia, while hypocalcemia is associated with an increased risk for anemia. Assessment of vitamin D and Ca²⁺ status may be valuable in the clinical management of anemia in the Saudi population.

Calcium is a noncompetitive inhibitor of DMT1 on the intestinal iron absorption process: empirical evidence and mathematical modeling analysis

Iron absorption is a complex and highly controlled process where DMT1 transports nonheme iron through the brush-border membrane of enterocytes to the cytoplasm but does not transport alkaline-earth metals such as calcium. However, it has been proposed that high concentrations of calcium in the diet could reduce iron bioavailability. In this work, we investigate the effect of intracellular and extracellular calcium on iron uptake by Caco-2 cells, as determined by calcein fluorescence quenching. We found that extracellular calcium inhibits iron uptake by Caco-2 cells in a concentration-dependent manner. Chelation of intracellular calcium with BAPTA did not affect iron uptake, which indicates that the inhibitory effect of calcium is not exerted through intracellular calcium signaling. Kinetic studies performed, provided evidence that calcium acts as a reversible noncompetitive inhibitor of the iron transport activity of DMT1. Based on these experimental results, a mathematical model was developed that considers the dynamics of noncompetitive inhibition using a four-state mechanism to describe the inhibitory effect of calcium on the DMT1 iron transport process in intestinal cells. The model accurately predicts the calcein fluorescence quenching dynamics observed experimentally after an iron challenge. Therefore, the proposed model structure is capable of representing the inhibitory effect of extracellular calcium on DMT1-mediated iron entry into the cLIP of Caco-2 cells. Considering the range of calcium concentrations that can inhibit iron uptake, the possible inhibition of dietary calcium on intestinal iron uptake is discussed.

Iron Deficiency in Adolescent and Young Adult German Athletes-A Retrospective Study

Background: Iron deficiency is a common phenomenon in sports and may lead to impaired physical performance. The aim of the study was to determine the frequency of iron deficiency in competitive athletes and to discuss the resulting consequences. Methods: The data of 629 athletes (339 male, 290 female) who presented for their annual basic sports medicine examination were investigated. Depending on age (<14 years, 15−17 years, ≥18−30 years), four groups ((I.) normal hemoglobin (Hb) and ferritin level (≥30 ng/mL for adults and 15−18-year-olds; ≥20 ng/mL, respectively, ≥15 ng/mL for adolescents and children), (II.) prelatent iron deficiency (ID) (normal Hb, low ferritin), (III.) latent ID (additionally elevated soluble transferrin receptor or decreased transferrin saturation) and (IV.) manifest anemia) were distinguished. In addition, the iron status and exercise capacity of different types of sports were compared. Results: Overall we found an iron deficiency of 10.9% in male (mainly in adolescence) and 35.9% in female athletes (emphasized in adolescence and young adulthood). There were no significant differences in iron status in regard to the different sport types or in maximum performance for the different groups of iron deficiency. Conclusions: Adolescent and female athletes are more likely to have an iron deficiency. Therapy concepts for athletes therefore should pay attention to iron-rich diets.

Calcium supplementation for prevention of primary hypertension

BACKGROUND

Hypertension is a major public health problem that increases the risk of cardiovascular and kidney diseases. Several studies have shown an inverse association between calcium intake and blood pressure, as small reductions in blood pressure have been shown to produce rapid reductions in vascular disease risk even in individuals with normal blood pressure ranges. This is the first update of the review to evaluate the effect of calcium supplementation in normotensive individuals as a preventive health measure.

OBJECTIVES

To assess the efficacy and safety of calcium supplementation versus placebo or control for reducing blood pressure in normotensive people and for the prevention of primary hypertension.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomised controlled trials up to September 2020: the Cochrane Hypertension Specialised Register, CENTRAL (2020, Issue 9), Ovid MEDLINE, Ovid Embase, the WHO International Clinical Trials Registry Platform, and the US National Institutes of Health Ongoing Trials Register, ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions.

SELECTION CRITERIA

We selected trials that randomised normotensive people to dietary calcium interventions such as supplementation or food fortification versus placebo or control. We excluded quasi-random designs. The primary outcomes were hypertension (defined as blood pressure ≥ 140/90 mmHg) and blood pressure measures.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, abstracted the data and assessed the risks of bias. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

The 2020 updated search identified four new trials. We included a total of 20 trials with 3512 participants, however we only included 18 for the meta-analysis with 3140 participants. None of the studies reported hypertension as a dichotomous outcome. The effect on systolic and diastolic blood pressure was: mean difference (MD) -1.37 mmHg, 95% confidence interval (CI) -2.08, -0.66; 3140 participants; 18 studies; I2 = 0%, high-certainty evidence; and MD -1.45, 95% CI -2.23, -0.67; 3039 participants; 17 studies; I2 = 45%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for those younger than 35 years was: MD -1.86, 95% CI -3.45, -0.27; 452 participants; eight studies; I2 = 19%, moderate-certainty evidence; MD -2.50, 95% CI -4.22, -0.79; 351 participants; seven studies ; I2 = 54%, moderate-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for those 35 years or older was: MD -0.97, 95% CI -1.83, -0.10; 2688 participants; 10 studies; I2 = 0%, high-certainty evidence; MD -0.59, 95% CI -1.13, -0.06; 2688 participants; 10 studies; I2 = 0%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for women was: MD -1.25, 95% CI -2.53, 0.03; 1915 participants; eight studies; I2 = 0%, high-certainty evidence; MD -1.04, 95% CI -1.86, -0.22; 1915 participants; eight studies; I2 = 4%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for men was MD -2.14, 95% CI -3.71, -0.59; 507 participants; five studies; I2 = 8%, moderate-certainty evidence; MD -1.99, 95% CI -3.25, -0.74; 507 participants; five studies; I2 = 41%, moderate-certainty evidence, respectively. The effect was consistent in both genders regardless of baseline calcium intake. The effect on systolic blood pressure was: MD -0.02, 95% CI -2.23, 2.20; 302 participants; 3 studies; I2 = 0%, moderate-certainty evidence with doses less than 1000 mg; MD -1.05, 95% CI -1.91, -0.19; 2488 participants; 9 studies; I2 = 0%, high-certainty evidence with doses 1000 to 1500 mg; and MD -2.79, 95% CI -4.71, 0.86; 350 participants; 7 studies; I2 = 0%, moderate-certainty evidence with doses more than 1500 mg. The effect on diastolic blood pressure was: MD -0.41, 95% CI -2.07, 1.25; 201 participants; 2 studies; I2 = 0, moderate-certainty evidence; MD -2.03, 95% CI -3.44, -0.62 ; 1017 participants; 8 studies; and MD -1.35, 95% CI -2.75, -0.05; 1821 participants; 8 studies; I2 = 51%, high-certainty evidence, respectively. None of the studies reported adverse events.

AUTHORS' CONCLUSIONS

An increase in calcium intake slightly reduces both systolic and diastolic blood pressure in normotensive people, particularly in young people, suggesting a role in the prevention of hypertension. The effect across multiple prespecified subgroups and a possible dose response effect reinforce this conclusion. Even small reductions in blood pressure could have important health implications for reducing vascular disease. A 2 mmHg lower systolic blood pressure is predicted to produce about 10% lower stroke mortality and about 7% lower mortality from ischaemic heart disease. There is a great need for adequately-powered clinical trials randomising young people. Subgroup analysis should involve basal calcium intake, age, sex, basal blood pressure, and body mass index. We also require assessment of side effects, optimal doses and the best strategy to improve calcium intake.

The Effect of Calcium Supplementation on Body Weight Before and During Pregnancy in Women Enrolled in the WHO Calcium and Preeclampsia Trial

INTRODUCTION

Obesity is a major and challenging public health problem. The aim of this substudy is to evaluate the effect of calcium supplementation on body weight in women recruited in the Calcium and Preeclampsia trial.

METHODS

Women were recruited before pregnancy and randomized to receive a calcium supplement containing 500 mg of elemental calcium or placebo until 20 weeks' gestation; all women received 1.5 g from 20 weeks until delivery.

RESULTS

A total of 630 women conceived during the study, 322 allocated to calcium and 308 to placebo. Among these, 230 allocated to calcium and 227 allocated to placebo had information on body weight at baseline and at 8 weeks' gestation. During the study period, women allocated to calcium had a mean weight increase of 1.1 (SD ±5.5) kg, whereas those allocated to placebo had a mean increase of 1.5 (SD ±6.1) kg, a mean difference of 0.4 kg (95% -0.4 (-1.4 to 0.6); P = .408). Women classified as obese at the start of the trial had a lower body weight gain at 8 weeks' gestation (1.0 kg; 95% CI: -3.2 to 1.2; P = .330) and at 32 weeks' gestation (2.1 kg; 95% CI: 5.6-1.3; P = .225) if they received calcium as compared to placebo. However, none of these differences were statistically significant.

CONCLUSION

The smaller increase in body weight found in women supplemented with 500 mg elemental calcium daily is quantitatively consistent with previous studies. However, in this study, the difference was not statistically significant.

Calcium supplementation for prevention of primary hypertension

BACKGROUND

Hypertension is a major public health problem that increases the risk of cardiovascular and kidney diseases. Several studies have shown an inverse association between calcium intake and blood pressure, as small reductions in blood pressure have been shown to produce rapid reductions in vascular disease risk even in individuals with normal blood pressure ranges. This is the first update of the review to evaluate the effect of calcium supplementation in normotensive individuals as a preventive health measure.

OBJECTIVES

To assess the efficacy and safety of calcium supplementation versus placebo or control for reducing blood pressure in normotensive people and for the prevention of primary hypertension.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomised controlled trials up to September 2020: the Cochrane Hypertension Specialised Register, CENTRAL (2020, Issue 9), Ovid MEDLINE, Ovid Embase, the WHO International Clinical Trials Registry Platform, and the US National Institutes of Health Ongoing Trials Register, ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions.

SELECTION CRITERIA

We selected trials that randomised normotensive people to dietary calcium interventions such as supplementation or food fortification versus placebo or control. We excluded quasi-random designs. The primary outcomes were hypertension (defined as blood pressure ≥ 140/90 mmHg) and blood pressure measures.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, abstracted the data and assessed the risks of bias. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

The 2020 updated search identified four new trials. We included a total of 20 trials with 3512 participants, however we only included 18 for the meta-analysis with 3140 participants. None of the studies reported hypertension as a dichotomous outcome. The effect on systolic and diastolic blood pressure was: mean difference (MD) -1.37 mmHg, 95% confidence interval (CI) -2.08, -0.66; 3140 participants; 18 studies; I² = 0%, high-certainty evidence; and MD -1.45, 95% CI -2.23, -0.67; 3039 participants; 17 studies; I² = 45%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for those younger than 35 years was: MD -1.86, 95% CI -3.45, -0.27; 452 participants; eight studies; I² = 19%, moderate-certainty evidence; MD -2.50, 95% CI -4.22, -0.79; 351 participants; seven studies ; I² = 54%, moderate-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for those 35 years or older was: MD -0.97, 95% CI -1.83, -0.10; 2688 participants; 10 studies; I² = 0%, high-certainty evidence; MD -0.59, 95% CI -1.13, -0.06; 2688 participants; 10 studies; I² = 0%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for women was: MD -1.25, 95% CI -2.53, 0.03; 1915 participants; eight studies; I² = 0%, high-certainty evidence; MD -1.04, 95% CI -1.86, -0.22; 1915 participants; eight studies; I² = 4%, high-certainty evidence, respectively. The effect on systolic and diastolic blood pressure for men was MD -2.14, 95% CI -3.71, -0.59; 507 participants; five studies; I² = 8%, moderate-certainty evidence; MD -1.99, 95% CI -3.25, -0.74; 507 participants; five studies; I² = 41%, moderate-certainty evidence, respectively. The effect was consistent in both genders regardless of baseline calcium intake. The effect on systolic blood pressure was: MD -0.02, 95% CI -2.23, 2.20; 302 participants; 3 studies; I² = 0%, moderate-certainty evidence with doses less than 1000 mg; MD -1.05, 95% CI -1.91, -0.19; 2488 participants; 9 studies; I² = 0%, high-certainty evidence with doses 1000 to 1500 mg; and MD -2.79, 95% CI -4.71, 0.86; 350 participants; 7 studies = 8; I² = 0%, moderate-certainty evidence with doses more than 1500 mg. The effect on diastolic blood pressure was: MD -0.41, 95% CI -2.07, 1.25; 201 participants; 2 studies; I² = 0, moderate-certainty evidence; MD -2.03, 95% CI -3.44, -0.62 ; 1017 participants; 8 studies; and MD -1.35, 95% CI -2.75, -0.05; 1821 participants; 8 studies; I² = 51%, high-certainty evidence, respectively. None of the studies reported adverse events.

AUTHORS' CONCLUSIONS

An increase in calcium intake slightly reduces both systolic and diastolic blood pressure in normotensive people, particularly in young people, suggesting a role in the prevention of hypertension. The effect across multiple prespecified subgroups and a possible dose response effect reinforce this conclusion. Even small reductions in blood pressure could have important health implications for reducing vascular disease. A 2 mmHg lower systolic blood pressure is predicted to produce about 10% lower stroke mortality and about 7% lower mortality from ischaemic heart disease. There is a great need for adequately-powered clinical trials randomising young people. Subgroup analysis should involve basal calcium intake, age, sex, basal blood pressure, and body mass index. We also require assessment of side effects, optimal doses and the best strategy to improve calcium intake.

Calcium-fortified foods in public health programs: considerations for implementation

Low calcium intake is common worldwide and can result in nutritional rickets in children and osteomalacia in adults. Calcium-fortified foods could improve calcium intake. However, there is limited calcium fortification experience, with technical and practical issues that may hamper its adoption. The objective of this landscape review is to summarize these issues to help policymakers guide the planning and design of calcium fortification as a public health strategy. One challenge is the low bioavailability of calcium salts (∼20-40%); thus, large amounts need to be added to food to have a meaningful impact. Solubility is important when fortifying liquids and acidic foods. Calcium salts could change the flavor, color, and appearance of the food and may account for 70-90% of the total fortification cost. Safety is key to avoid exceeding the recommended intake; so the amount of added calcium should be based on the target calcium intake and the gap between inadequate and adequate levels. Monitoring includes the quality of the fortified food and population calcium intake using dietary assessment methods. Calcium fortification should follow regulations, implemented in an intersectorial way, and be informed by the right to health and equity. This information may help guide and plan this public health strategy.

Regulatory and Policy-Related Aspects of Calcium Fortification of Foods. Implications for Implementing National Strategies of Calcium Fortification

Daily calcium intake is well below current recommendations in most low- and middle-income countries (LMICs). Calcium intake is usually related to bone health, however an adequate calcium intake has also been shown to reduce hypertensive disorders of pregnancy, lower blood pressure and cholesterol values, and to prevent recurrent colorectal adenomas. Fortification of foods has been identified as a cost-effective strategy to overcome micronutrient gaps in public health. This review summarizes regulatory aspects of fortification of commonly consumed foods with micronutrients, with an emphasis on calcium. We selected a convenient sample of 15 countries from different WHO regions and described the regulatory framework related to calcium fortification of staple foods. We assessed the relevant policies in electronic databases including the WHO Global database on the Implementation of Nutrition Action (GINA) for fortification policies and the Global Fortification Data Exchange Database, a fortification database developed and maintained by Food Fortification Initiative (FFI), Global Alliance for Improved Nutrition (GAIN), Iodine Global Network (IGN), and Micronutrient Forum. Food fortification with micronutrients is widely used in many of the selected countries. Most countries had national legislation for the addition of micronutrients to staple foods, especially wheat flour. These national legislations, that includes regulations and standards, can provide the framework to consider the implementation of adding calcium to the fortification strategies, including the selection of the adequate food vehicle to reach the targeted population at risk safely. The strategy to include calcium in the fortification mix in fortified staple foods seems promising in these countries. However, potential undesired changes on the organoleptic characteristics of fortified foods and products thereof, and operational feasibility at the manufacturing site should be evaluated by the stakeholders during the planning stage. Codex Alimentarius standards should be considered by regulators in order to assure adherence to international standards. While the selected countries already have established national regulations and/or standards for fortification of key staple food vehicles, and there are experiences in the implementation of fortification of some staple foods, national food intake surveys can help plan, design, and modify existing fortification programs as well as monitor food and nutrient consumption to assess risk and benefits.

Calcium Intake and Health

There are striking inequities in calcium intake between rich and poor populations. Appropriate calcium intake has shown many health benefits, such as reduction of hypertensive disorders of pregnancy, lower blood pressure particularly among young people, prevention of osteoporosis and colorectal adenomas, lower cholesterol values, and lower blood pressure in the progeny of mothers taking sufficient calcium during pregnancy. Studies have refuted some calcium supplementation side effects like damage to the iron status, formation of renal stones and myocardial infarction in older people. Attention should be given to bone resorption in post-partum women after calcium supplementation withdrawal. Mechanisms linking low calcium intake and blood pressure are mediated by parathyroid hormone raise that increases intracellular calcium in vascular smooth muscle cells leading to vasoconstriction. At the population level, an increase of around 400-500 mg/day could reduce the differences in calcium intake between high- and middle-low-income countries. The fortification of food and water seems a possible strategy to reach this goal.

Calcium in drinking water: effect on iron stores in Danish blood donors-results from the Danish Blood Donor Study

BACKGROUND

Studies confirm that calcium inhibits iron absorption. Danish tap water comes from groundwater, which contains varying amounts of calcium depending on the subsoil. We investigated the association of calcium in drinking water with iron levels in Danish blood donors.

STUDY DESIGN AND METHODS

We used data on Danish blood donors including dietary and lifestyle habits, blood donation history, and physiologic characteristics including measures of ferritin levels along with information on area of residence from The Danish Blood Donor Study. Data on calcium levels in groundwater ("water hardness") were obtained through the Geological Survey of Denmark and Greenland. We performed multiple linear and logistic regression analyses to evaluate the effect of water hardness on ferritin levels and risk of having iron deficiency (defined as ferritin levels <15 ng/mL), stratified by sex.

RESULTS

There was a significant negative association between water hardness and ferritin levels in both men and women. Risk of iron deficiency was correspondingly increased in both men (odds ratio [OR], 1.55; 95% confidence interval [CI], 1.14-2.12) and women (OR, 1.20; 95% CI, 1.03-1.40) with increasing water hardness. In analyses restricted to individuals who received supplemental iron tablets no significant association between groundwater hardness and ferritin levels was observed.

CONCLUSIONS

As measured by ferritin levels, residential drinking water calcium content is associated with blood donors- iron levels and risk of iron deficiency. However, effect sizes are small.

Calcium supplementation for prevention of primary hypertension

BACKGROUND

Hypertension is a major public health problem that increases the risk of cardiovascular and kidney diseases. Several studies have shown an inverse association between calcium intake and blood pressure. As small reductions in blood pressure have been shown to produce rapid reductions in vascular disease risk even in individuals with normal blood pressure ranges, this review intends to evaluate the effect of calcium supplementation in normotensive individuals as a preventive health measure.

OBJECTIVES

To assess the efficacy and safety of calcium supplementation versus placebo or control for reducing blood pressure in normotensive people.

SEARCH METHODS

We searched the Cochrane Hypertension Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, MEDLINE In-Process, EMBASE and ClinicalTrials.gov for randomised controlled trials up to October 2014. The WHO International Clinical Trials Registry Platform (ICTRP) is searched for inclusion in the Group's Specialised Register. We also reviewed reference lists from retrieved studies and contacted authors of relevant papers. We applied no language restrictions.

SELECTION CRITERIA

We selected trials that randomised normotensive people to dietary calcium interventions such as supplementation or food fortification versus placebo or control. We excluded quasi-random designs. The primary outcomes were hypertension (defined as blood pressure ≥ 140/90 mmHg) and blood pressure measures.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, abstracted the data and assessed the risks of bias.

MAIN RESULTS

We included 16 trials with 3048 participants. None of the studies reported hypertension as a dichotomous outcome. The effect on systolic and diastolic blood pressure was mean difference (MD) -1.43 mmHg (95% confidence interval (CI) -2.15 to -0.72) and -0.98 mmHg (95%CI -1.46 to -0.50) respectively. The effect on systolic and diastolic blood pressure for those younger than 35 years (7 trials with 399 participants) was -2.11 mmHg (95%CI -3.58 to -0.64) / -2.61 mmHg (95% CI -3.74, -1.49). The effect on systolic and diastolic blood pressure for those 35 years or more (9 trials with 2649 participants) was -0.96 mmHg (95%CI -1.83 to -0.09) / -0.59 mmHg (95%CI -1.13 to -0.06). The effect on systolic and diastolic blood pressure for women (6 trials with 1823 participants) was -1.45 mmHg (95% CI -2.78 to -0.12) / -0.92 mmHg (95% CI -1.71 to -0.14). The effect on systolic and diastolic blood pressure for men (5 trials with 617 participants) was -2.07 (95%CI -3.56 to -0.59] / -1.91 (95%CI -2.80 to -1.02).The quality of evidence for each of these outcomes was high. The effect is consistent in both genders regardless of baseline calcium intake.The effect on systolic blood pressure was 0.08 mmHg (95% CI -2.16 to 2.32) with doses less than 1000 mg, -1.14 mmHg (95% CI -2.01 to -0.27) with 1000 - 1500 mg, and -2.79 mmHg (95% CI -4.71 to -0.86) with more than 1500 mg. The effect on diastolic blood pressure was -0.54 mmHg (95% CI -2.23 to 1.15), -0.71 mmHg (95% CI -1.37 to -0.06) and -1.43 mmHg (95% CI -2.22 to -0.64) respectively. The quality of evidence for each of these outcomes was high.None of the studies reported adverse events.

AUTHORS' CONCLUSIONS

An increase in calcium intake slightly reduces both systolic and diastolic blood pressure in normotensive people, particularly in young people, suggesting a role in the prevention of hypertension. These results should be interpreted with caution, since the proposed biological mechanism explaining the relationship between calcium and blood pressure has not been fully confirmed. The effect across multiple prespecified subgroups and a possible dose response effect reinforce this conclusion. Even small reductions in blood pressure could have important health implications for reducing vascular disease.There is a great need for adequately-powered clinical trials randomising young people. Subgroup analysis should involve basal calcium intake, age, sex, basal blood pressure, and body mass index. We also require assessment of side effects, optimal doses and the best strategy to improve calcium intake.

The Importance of Milk and other Animal-Source Foods for Children in Low-Income Countries

Background

Milk and other animal-source foods are concentrated dietary sources of macro- and micronutrients. Despite a global increase in milk production and consumption over the past decades, milk and other animal-source foods are often lacking in the diets of children in developing countries.

Objective

To evaluate the importance of milk and other animal-source food intake in promoting the growth, development, and health of children in low-income countries.

Methods

Original research articles describing observational and intervention studies with unfortified milk, fortified milk, and other animal-source foods in children were identified by searching the PubMed database.

Results

Consumption of milk and other animal-source foods by undernourished children improves anthropometric indices and cognitive function and reduces the prevalence of biochemical and functional nutritional deficiencies, reducing morbidity and mortality. Unfortified and fortified milk used in supplementation trials has been well tolerated and widely accepted by parents and children.

Conclusions

To improve the dietary quality of children in low-income countries and further the effort to eradicate extreme poverty and hunger in accordance with the United Nations Millennium Development Goals, additional research is necessary to identify and implement programs and policy supporting increased intake of milk and other animal-source foods.