World Health Organization 2009

This document identifies knowledge gaps and recommends research priorities in order to build an evidence base to inform decisions on managing processed” drinking-water. This is important because of increasing consumption of water arising from advanced treatment processes such as desalination and uncertainty about the resulting heatlh implications.

The World Health Organization (WHO) assembled a diverse group of nutrition, medical, epidemiological and other scientific experts and water technologists at the Pan American Health Organization in Washington, DC, USA, on 27–28 April 2006 to address the possible role of drinking-water containing calcium and/or magnesium as a contribution to the daily intake of those minerals.

The overarching issue addressed was whether consumption of drinking-water containing a relatively small contribution to total daily dietary intake of calcium and/or magnesium would provide positive health benefits, especially with respect to cardiovascular disease mortality (the so-called hard water cardiovascular disease benefits hypothesis”), in the population, particularly in people whose dietary intake was deficient in either of those nutrients. The meeting of experts immediately followed the International Symposium on Health Aspects of Calcium and Magnesium in Drinking Water, which was organized by NSF International and the International Life Sciences Institute in Baltimore, MD, USA.

Both calcium and magnesium are essential to human health. Inadequate intake of either nutrient can impair health. Recommended daily intakes of each element have been set at national and international levels. Food is the principal source of both calcium and magnesium. Dairy products are the richest sources of dietary calcium, contributing over 50% of the total calcium in many diets. Some plant foods, including legumes, green leafy vegetables and broccoli, can also contribute to dietary calcium, but the content is lower than in dairy products, and the bioavailability of calcium in plant foods can be low if the concentration of oxalate or phytate is high. Dietary sources of magnesium are more varied; dairy products, vegetables, grain, fruits and nuts are important contributors.

Individuals vary considerably in their needs for and consumption of these elements. Available evidence suggests that, because of food habits, many people in most countries fail to obtain from their diets the recommended intakes of one or both of these nutrients. While the concentrations of calcium and magnesium in drinking-water vary markedly from one supply to another, mineral-rich drinking-waters may provide substantial contributions to total intakes of these nutrients in some populations or population subgroups. Water treatment processes can affect mineral concentrations and, hence, the total intake of calcium and magnesium for some individuals.

On the basis of the findings of the World Health Organization (WHO) meeting of experts held in Rome, Italy, in 2003 to discuss nutrients in drinkingwater (WHO 2005), the present group focused its consideration on calcium and magnesium, for which, next to fluoride, evidence of health benefits associated with their presence in drinking-water is strongest. The present group also noted that the issue of fluoride was addressed by the Rome meeting in detail and adopted its review and recommendations (see below). In addition, the group concluded that other elements may also have health relevance and should be considered by future groups.

1.2 CALCIUM

Over 99% of total body calcium is found in bones and teeth, where it functions as a key structural element. The remaining body calcium functions in metabolism, serving as a signal for vital physiological processes, including vascular contraction, blood clotting, muscle contraction and nerve transmission. Inadequate intakes of calcium have been associated with increased risks of osteoporosis, nephrolithiasis (kidney stones), colorectal cancer, hypertension and stroke, coronary artery disease, insulin resistance and obesity.

Most of these disorders have treatments but no cures. Owing to a lack of compelling evidence for the role of calcium as a single contributory element in relation to these diseases, estimates of calcium requirement have been made on the basis of bone health outcomes, with the goal of optimizing bone mineral density. Calcium is unique among nutrients, in that the body’s reserve is also functional: increasing bone mass is linearly related to reduction in fracture risk.

1.2.1 Osteoporosis

Osteoporosis is a condition of skeletal fragility characterized by low bone mass and by microarchitectural deterioration of bone tissue, with a consequent increase in risk of fracture. Calcium is the largest constituent of bone, comprising 32% by weight. A large body of primary evidence from randomized controlled trials shows that increasing calcium intake, especially in those who have had habitually low calcium intakes, increases bone mass during growth andreduces bone loss and fracture risk late in life. Osteoporosis is one of the most prevalent of age-related diseases.

1.2.2 Kidney stones

The relationship between calcium intake and the incidence of kidney stones is dependent on whether calcium is consumed with food or separately. Calcium that reaches the lower small intestine actually protects against kidney stones by binding oxalic acid (a precursor to common kidney stones) in foods and reducing its absorption. Calcium ingested from water together with food would have the same effect. Epidemiological evidence is strong that dietary calcium reduces the incidence of kidney stones. In contrast, the results of a large randomized trial1 suggest an increased risk of kidney stones associated with calcium supplements, possibly because the calcium was not ingested with food or the supplements were taken by those who exceeded the upper level of 2500 mg/day.

1.2.3 Hypertension and stroke

Hypertension (high blood pressure) is a risk factor for several diseases. It is an important health problem especially in developed countries, but also in developing countries. Although hypertension is multifactorial in origin, adequate calcium intake has been associated with lowered risk of elevated blood pressure in some, but not all, studies. A clear mechanism has not been identified. Dairy products, more than calcium, per se, have been associated with reduced blood pressure in randomized prospective studies and with reduced risk of stroke in prospective studies.

1.2.4 Insulin resistance

Insulin resistance is associated with type 2 diabetes mellitus, the prevalence of which is escalating with the rise in obesity worldwide. Dietary calcium may be implicated in the etiology of insulin resistance through the fluctuations in calcium-regulating hormones in states of calcium sufficiency and deficiency. This is an area of active research; thus, it is premature to use such a clinical outcome as the basis for deriving recommendations for dietary intake of calcium. 1 From the Women’s Health Initiative, a 15-year programme established by the United States National Institutes of Health in 1991. Expert consensus

 1.2.5 Vulnerable populations

Those individuals who avoid dairy products or lack access to them may be at increased risk of calcium deficiency. Formula-fed infants will not normally be at risk from deficient or excess amounts of calcium. Even extremely low or high calcium concentrations in water would not lead to absorption of unphysiological amounts of calcium from infant formula reconstituted with the water. If, however, other feeds are used that do not provide the calcium content of fullstrength formula, then water may represent an important source of the mineral for the infants.

1.2.6 Excess calcium intakes

To a great extent, individuals are protected from excess intakes of calcium by a tightly regulated intestinal absorption mechanism through the action of 1,25- dihydroxyvitamin D, the hormonally active form of vitamin D. When absorbed calcium is in excess of need, the excess is excreted by the kidney in most healthy people. Concern for excess calcium intake is directed primarily to those who are prone to milk alkali syndrome (the simultaneous presence of hypercalcaemia, metabolic alkalosis and renal insufficiency) and hypercalcaemia. Although calcium can interact with iron, zinc, magnesium and phosphorus within the intestine, thereby reducing the absorption of these minerals, available data do not suggest that these minerals are depleted when humans consume diets containing calcium above the recommended levels. For example, even though high intakes of calcium can exert acute effects on iron absorption, there is no evidence of reduced iron status or iron stores with long-term calcium supplementation

1.3 MAGNESIUM

Magnesium is the fourth most abundant cation in the body and the second most abundant cation in intracellular fluid. It is a cofactor for some 350 cellular enzymes, many of which are involved in energy metabolism. It is also involved in protein and nucleic acid synthesis and is needed for normal vascular tone and insulin sensitivity. Low magnesium levels are associated with endothelial dysfunction, increased vascular reactions, elevated circulating levels of Creactive protein and decreased insulin sensitivity. Low magnesium status has been implicated in hypertension, coronary heart disease, type 2 diabetes mellitus and metabolic syndrome.

1.3.1 Hypertension

Magnesium deficiency has been implicated in the pathogenesis of hypertension, with some epidemiological and experimental studies demonstrating a negative correlation between blood pressure and serum magnesium levels. However, data from clinical studies have been less convincing.

1.3.2 Cardiac arrhythmias

Cardiac arrhythmias of ventricular and atrial origin have been reported in patients with hypomagnesaemia. Indeed, a serious cardiac arrhythmia, Torsade de Pointes, is treated with intravenous magnesium therapy.

1.3.3 Pre-eclampsia

Pre-eclampsia (defined as hypertension after 20 weeks of gestation) with proteinuria has been treated with magnesium salts for many decades. A recent clinical trial (Altman et al. 2002) using magnesium sulfate showed a 50% decreased risk of eclampsia.

1.3.4 Atherosclerosis

Animal studies have documented an inverse (protective) relationship between magnesium intake and the rate or incidence of atherosclerosis.

1.3.5 Coronary heart disease

In humans, there is evidence for an inverse (protective) relationship between magnesium and coronary heart disease. Three cross-sectional studies have now documented an inverse relationship between the concentration of C-reactive protein (a proinflammatory marker that is a risk factor for coronary heart disease) and magnesium intake or serum magnesium concentration, suggesting that magnesium may have an anti-inflammatory effect.

1.3.6 Diabetes mellitus

Several studies have documented the importance of magnesium in type 2 diabetes mellitus. Two recent studies have documented an inverse (protective) relationship between magnesium intake and risk of developing type 2 diabetes mellitus. Oral magnesium supplementation improves insulin sensitivity and metabolic control in type 2 diabetes mellitus.

1.3.7 Magnesium depletion status

Alcoholism and intestinal malabsorption are conditions associated with magnesium deficiency. Certain drugs, such as diuretics, some antibiotics and some chemotherapy treatments, increase the loss of magnesium through the kidney.

1.3.8 Hypermagnesaemia

The major cause of hypermagnesaemia is renal insufficiency associated with a significantly decreased ability to excrete magnesium. Increased intake of magnesium salts may cause a change in bowel habits (diarrhoea), but seldom causes hypermagnesaemia in persons with normal kidney function.

1.3.9 Gastrointestinal function

Drinking-water in which both magnesium and sulfate are present in high concentrations can have a laxative effect, although data suggest that consumers adapt to these levels as exposures continue. Laxative effects have also been associated with excess intake of magnesium taken in the form of supplements, but not with magnesium in diet.

Read full WHO Report

http://apps.who.int/iris/bitstream/10665/43836/1/9789241563550_eng.pdf?ua=1

Additional Readings

The high heart health value of drinking-water magnesium  Andrea Rosanoff ⇑http://www.mgwater.com/rosanoff_high_heart_health_value_of_drinking_water_magnesium2013.pdf