Improving Calcium Intakes and Calcium Bioavailability in the Population18

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The dietary deficiency of Ca identified in some population groups may be addressed in a number of ways. This includes changing eating behavior at the population level by increasing the consumption of foods that are naturally rich in Ca (e.g., milk and milk products), Ca fortification of foods consumed by target groups, or increasing Ca intakes from Ca supplements. These may be seen as complementary rather than alternative strategies, and each has advantages and disadvantages.31 For example, it is notoriously difficult to achieve changes in the diet of entire populations, and thus persuading individuals to consume more dairy produce represents a considerable challenge. The use of Ca supplements can be effective in increasing Ca intake in individuals who consume them regularly, but it has limited effectiveness at the population level due to the poor compliance with supplement use.31 Ca-fortified food products could provide additional choices for meeting Ca requirements; however, attention should be paid to the selection of products so that they reach the target groups (i.e., those population groups who have the greatest difficulty in meeting Ca requirements). Moreover, Ca intake cannot be increased unlimitedly because, as recommended by the National Institutes of Health (NIH) Consensus Conference on Optimal Calcium Intake, "practices that might encourage total calcium intake to approach or exceed 2000 mg/d seem more likely to produce adverse effects and should be monitored closely."12 That topic has recently been reviewed by Whiting and Wood who cautioned that supplemental foods should "prevent overconsumption of calcium while still promoting improved calcium nutriture.. ,."53

Besides the amount of Ca in the diet, the absorption of dietary Ca in foods is also a critical factor in determining the availability of Ca for bone development and maintenance. Thus, and because dietary factors that alter Ca absorption also modify Ca retention,54 there is a need to identify food components and/or functional food ingredients that may enhance Ca absorption in order to optimise Ca bioavailability from foods.54,55 As stated by Weaver and Liebman:

Increasing para cellular [sic] absorption is promising because it is not limited by becoming saturated, it is vitamin D independent, and it occurs throughout the length of the intestine in contrast to active absorption which is dominant in the duodenum. [□ ] Ideal compounds would be those that could be incorporated into Ca-containing food to enhance absorption of Ca but would have only transient effect, so that transfer of undesirable organisms and ions would be minimized.54

A number of food constituents have attracted attention as potential enhancers of Ca absorption like lactose, casein phosphopeptides,56,57 and nondigestible oligosaccharides.1118 According to Berrocal et al., the phosphopeptides have the capacity to chelate Ca and to prevent the precipitation of its phosphate salts, thus helping to maintain a high concentration of soluble Ca in the intestinal lumen.58 There is some experimental, but only limited, human evidence that casein phosphopeptides increase Ca absorption.42,44,59,60 Therefore, the significance of these phosphopeptides for enhancing Ca absorption in humans remains unclear. Ziegler and Fomon showed that Ca absorption in human infants was significantly higher from a soy-based infant formula containing lactose as compared to a similar formula containing a mixture of starch hydrolysate and sucrose.61 Enhancement of Ca absorption by lactose has also been reported in rats.62-64 However, studies on the effect of lactose on Ca absorption in human adults generally have failed to demonstrate this effect. Miller, in a critical review of this area, concluded that it is likely that lactose enhances Ca absorption in human infants and in rats, while, at levels normally present in milk, lactose does not have a significant effect on Ca absorption by healthy adults consuming normal diets.65 Recently, Van den Heuvel et al. have reported that consumption of lactulose (5 or 10 g/d) or transgalactooligosaccharides (20 g/d) increased Ca absorption in postmenopausal women in a dose-responsive manner.66

Increasing Ca absorption (either directly or indirectly via an increase in Ca intake) also affects bone turnover, e.g., by down-regulating bone resorption67 and leads to increased Ca retention.

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