Léon Guéguen

The Bioavailability of Dietary Calcium

This update focuses on the bioavailability of dietary calcium for humans. Fundamentals of calcium metabolism, intestinal absorption, urinary excretion and balance are recalled. Dietary factors, especially lactose and other milk components, influencing calcium bioavailability at intestinal and renal levels are reviewed. A critical examination of all the methods used for evaluating calcium bioavailability is made. This includes in vitro assays, classical and isotopic balances, urinary excretion, isotope labeling in the urine, plasma and bones, long term evaluation of bone mineralization and the use of biological bone markers. Importance and advantages of animal models are discussed. The state of the art in the comparative bioavailability of calcium in foods is detailed including a comparison of sources of calcium (dairy products and calcium salts) in human studies and in some animal studies, casein phosphopeptides, proteins, lactose and lactase and their relation with calcium bioavailability (in humans and rats). An update on the consumption of dairy products and bone mass is presented. Emphasis on peculiarities and advantages of calcium in milk and dairy products is given.

Minerals and vitamins in bone health: the potential value of dietary enhancement.

Nutrition is important to bone health, and a number of minerals and vitamins have been identified as playing a potential role in the prevention of bone diseases, particularly osteoporosis. Despite this, there is currently no consensus on maximum levels to allow in food or as dietary supplements. The benefits of supplementation of populations at risk of osteoporosis with Ca and vitamin D are well established. Prolonged supplementation of Ca and vitamin D in elderly has been shown to prevent bone loss, and in some intervention studies to prevent fragility fractures. Although P is essential to bone health, the average intake is considered to be more than sufficient and supplementation could raise intake to adverse levels. The role of vitamin K in bone health is less well defined, though it may enhance the actions of Ca and vitamin D. Sr administered in pharmacological doses as the ranelate salt was shown to prevent fragility fractures in postmenopausal osteoporosis. However, there is no hard evidence that supplementation with Sr salts would be beneficial in the general population. Mg is a nutrient implicated in bone quality, but the benefit of supplementation via foodstuffs remains to be established. A consensus on dietary supplementation for bone health should balance the risks, for example, exposure of vulnerable populations to values close to maximal tolerated doses, against evidence for benefits from randomised clinical trials, such as those for Ca and vitamin D. Feedback from community studies should direct further investigations and help formulate a consensus on dietary supplementation for bone health.

Higher calcium urinary loss induced by a calcium sulphate-rich mineral water intake than by milk in young women

It is well known that the intestinal availability of Ca from Ca-rich mineral waters is equivalent to that of milk Ca. However, the effect of associated anions on Ca urinary loss needs to be addressed. The aim of the current study was to compare, under ordinary conditions of consumption, milk and a SO4-rich mineral water as the Ca provider in a large number of subjects consuming the same quantity of Ca from the two sources in a crossover study lasting for an extended period. Thirty-seven healthy women completed a 12-week protocol, divided into four periods of 3 weeks (W). In the first (W1-3) and third (W6-9) periods, dietary Ca intake was restricted to 600 mg/d. In the second (W4-6) and final (W10-12) periods, either 400 ml/d medium-fat milk or 1 litre of a Ca- and SO4-rich mineral water, each providing about 480 mg Ca/d, was added to the diet in a random manner. Dietary evaluation, blood and urinary measures were performed during the last week (W6 and W12) of each Ca supplementation period. The urinary excretion of Ca was higher (0.5 mmol/d more) with water than with milk (P<0.001). An examination of all the dietary factors known to influence calciuria suggested that the acidogenic action of SO4 was responsible for this increased calciuria. Thus, despite an equal Ca intake and assuming an unchanged intestinal absorption, these results suggest that Ca balance is better with milk consumption than with CaSO4-rich water.

Le calcium du lait : fonctions, intérêts, besoins, biodisponibilité

Resume Le calcium corporel, dont 99 % se trouvent dans le squelette, est surtout connu comme facteur alimentaire de prevention de l’osteoporose. Son role ne se limite pourtant pas a la constitution de l’os, car la faible part extra-osseuse est indispensable a d’innombrables fonctions vitales. Le calcium intervient aussi, comme le montrent de plus en plus d’etudes, dans la prevention de troubles aussi divers que l’hypertension arterielle, la lithiase renale, l’obesite, le cancer colorectal. Il est donc important de se rapprocher des apports nutritionnels conseilles (ANC) qui varient, selon l’âge et l’etat physiologique, de 800 a 1 200 mg de calcium par jour. De tels apports demeurent justifies par les besoins nets de croissance ou de lactation, mais aussi par les pertes endogenes incompressibles urinaire, fecale et sudorale. De plus, l’absorption intestinale est limitee et depasse rarement 40 % du calcium ingere. L’alimentation courante permet difficilement d’atteindre les apports conseilles, notamment chez les adolescentes et les personnes âgees qui ne consomment pas assez de produits laitiers. En effet, le calcium du lait represente plus des deux tiers de la quantite consommee. Tous les autres aliments courants, a l’exception de quelques legumes verts, des fruits secs et des eaux minerales calciques, sont tres pauvres en calcium. De plus, le calcium vegetal, souvent associe a des phytates ou oxalates, est moins disponible que le calcium du lait et des produits laitiers qui ne contiennent pas de facteurs inhibiteurs de l’absorption. La perte urinaire obligatoire de calcium est souvent determinante pour le bilan calcique. Elle est accrue par les constituants acidogenes du regime, notamment les sulfates, mais les proteines du lait n’augmentent pas significativement la calciurie car le phosphore, et peut-etre le potassium, apportes simultanement compensent l’effet oppose des sulfates. La speciation chimique du calcium du lait et les composants potentiellement favorables a sa biodisponibilite qui lui sont associes en font incontestablement, quantitativement et qualitativement, le calcium alimentaire de reference.

Higher calcium urinary loss induced by a calcium sulphate-rich mineral water intake than by milk in young women â reply by Brandolini et al.

It is well known that the intestinal availability of Ca from Ca-rich mineral waters is equivalent to that of milk Ca. However, the effect of associated anions on Ca urinary loss needs to be addressed. The aim of the current study was to compare, under ordinary conditions of consumption, milk and a SO4-rich mineral water as the Ca provider in a large number of subjects consuming the same quantity of Ca from the two sources in a crossover study lasting for an extended period. Thirty-seven healthy women completed a 12-week protocol, divided into four periods of 3 weeks (W). In the first (W1-3) and third (W6-9) periods, dietary Ca intake was restricted to 600 mg/d. In the second (W4-6) and final (W10-12) periods, either 400 ml/d medium-fat milk or 1 litre of a Ca- and SO4-rich mineral water, each providing about 480 mg Ca/d, was added to the diet in a random manner. Dietary evaluation, blood and urinary measures were performed during the last week (W6 and W12) of each Ca supplementation period. The urinary excretion of Ca was higher (0.5 mmol/d more) with water than with milk (P<0.001). An examination of all the dietary factors known to influence calciuria suggested that the acidogenic action of SO4 was responsible for this increased calciuria. Thus, despite an equal Ca intake and assuming an unchanged intestinal absorption, these results suggest that Ca balance is better with milk consumption than with CaSO4-rich water.