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CURATOR
A pinboard by
Megan Beggs

PhD student, University of Alberta

PINBOARD SUMMARY

Understanding how infants and children absorb and retain dietary calcium for appropriate growth

Calcium is essential in the body, partly because it forms the foundation of bone structure. Bone growth occurs rapidly in infancy and continues throughout childhood, with bone mass peaking in early adulthood and then declining throughout the rest of life. It is, therefore, crucial to build strong bones during childhood. As a pediatric dietitian, I have experience caring for infants and children who are at risk of poor bone health due to factors that may include prematurity, gut disease, and kidney disease. Unfortunately, we do not fully understand the normal physiology of calcium homeostasis in children and therefore have failed to advance health care outcomes for this vulnerable population.

The intestines, kidneys, and bones maintain calcium homeostasis. Calcium enters the body through the intestines and is retained by the kidneys. Unfortunately, how the body absorbs and holds on to enough calcium to maintain a positive calcium balance required for appropriate growth is not clearly understood. We have detailed the current state of knowledge in this field in a recent review. Our major research aim is to understand this phenomenon. The first objective is to understand the molecular details of calcium absorption across the small intestine early in life. To date, using molecular biology and electrophysiology in a mouse model, we have identified novel absorption pathways that exist in the distal small intestine only during infancy. Our second objective will be to determine the mechanisms mediating the drastic alterations noted in our first objective. We hypothesize that bioactive compounds present in breast milk facilitate expression of the novel pathways observed. Our third objective is to determine post natal alterations in calcium reabsorption in the kidney.

Overall, results of this research plan will advance our knowledge of physiology that is critical to appropriate postnatal development. Understanding how dietary calcium is absorbed from the intestine of infants and children will inform adequate calcium intake throughout growth in healthy and ill populations. The results of this research will have further wide-ranging impact including optimizing delivery of calcium in infant formulas and the dairy industry. This research will also provide potential drug targets for diseases caused by disrupted calcium balance and thus lay the foundation for future measures to improve the health and care of infants and children.

7 ITEMS PINNED

Expression of Trans- and Paracellular Calcium and Magnesium Transport Proteins in Renal and Intestinal Epithelia During Lactation.

Abstract: Significant alterations in maternal calcium (Ca2+) and magnesium (Mg2+) balance occur during lactation. Ca2+ is the primary divalent cation mobilized into breast milk by demineralization of the skeleton and alterations in intestinal and renal Ca2+ transport. Mg2+ is also concentrated in breast milk, but the underlying mechanisms are not well understood. To determine the molecular alterations in Ca2+ and Mg2+ transport in the intestine and kidney during lactation, 3 groups of female mice consisting of either non-pregnant controls, lactating mice, or mice undergoing involution were examined. The fractional excretion of Ca2+, but not Mg2+, rose significantly during lactation. Renal 1-alpha hydroxylase and 24-OHase mRNA levels increased markedly as did plasma 1,25 dihydroxyvitamin D levels. This was accompanied by significant increases in intestinal expression of Trpv6 and S100g in lactating mice. However, no alterations in the expression of cation permeable claudins (-2, -12 or -15) were found in the intestine. In kidney, increased expression of Trpv5 and Calb1 was observed during lactation, while no changes in claudins involved in Ca2+ and Mg2+ transport (-2, -14, -16 or -19) were found. Consistent with the mRNA expression, both Calbindin-D28K and TRPV5 protein expression increased. Colonic Trpm6 expression increased during lactation, while renal Trpm6 remained unaltered. In conclusion, proteins involved in transcellular Ca2+ and Mg2+ transport pathways increase during lactation, while expression of paracellular transport proteins remained unchanged. Increased fractional Ca2+ excretion can be explained by vitamin D-dependent intestinal hyperabsorption and bone demineralization, despite enhanced transcellular Ca2+ uptake by the kidney.

Pub.: 26 May '17, Pinned: 23 Aug '17

Calcium to phosphorus ratio, essential elements and vitamin D content of infant foods in the UK: possible implications for bone health.

Abstract: Adequate intake of calcium and phosphorus in the appropriate ratio of 1-2:1 (Ca:P), in addition to magnesium and vitamin D, is vital for bone health and development of an infant. In this feasibility study, the ratio of Ca:P in conjunction with vitamin D and other essential elements (Cu, Fe, K, Mg, Na, and Zn) in a range of commercial infant food products in the UK is investigated. The elemental analysis was carried out using inductively coupled plasma optical emission spectrometry, and vitamin D levels were determined using an enzyme-linked immunosorbent assay. The quantitative data were further evaluated, based on a standardized menu, to measure the total daily intake of an infant aged 7-12 months against the Reference Nutrient Intake. The results from the study show that the Ca:P ratio of the infant's total dietary intake was within the recommended range at 1.49:1. However, the level of intake for each of the nutrients analyzed, with the exception of sodium, was found to be above the Reference Nutrient Intake, which warrants further investigation in relation to both micronutrient interactions and in situations where the intake of fortified infant formula milk is comprised. Finally, as the study is the first to include consumption of infant snack products, the level of total calorie intake was also calculated in order to assess the total daily estimated energy intake; the results indicate that energy intakes exceed recommendations by 42%, which may have implications for obesity.

Pub.: 10 Sep '16, Pinned: 23 Aug '17