Calcium, absorption

Calcium Absorption. Phytates in cereal grains have also been reported to interfere with the absorption of calcium. However, a long-term study indicated a retention of calcium in subjects that consume large amounts of bread made with high extraction of flour (19). 

Vitamins A, D, and E are required by mminants and, therefore, their supplementation is sometimes necessary. Vitamin A [68-26-8] is important in maintaining proper vision, maintenance and growth of squamous epitheHal ceUs, and bone growth (23). Vitamin D [1406-16-2] is most important for maintaining proper calcium absorption from the small intestine. It also aids in mobilizing calcium from bones and in optimizing absorption of phosphoms from the small intestine (23). Supplementation of vitamins A and D at their minimum daily requirement is recommended because feedstuffs are highly variable in their content of these vitamins. 

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

A major regulator of bone metabolism and calcium homeostasis, parathyroid hormone (PTH) is stimulated through a decrease in plasma ionised calcium and increases plasma calcium by activating osteoclasts. PTH also increases renal tubular calcium re-absorption as well as intestinal calcium absorption. Synthetic PTH (1-34) has been successfully used for the treatment of osteoporosis, where it leads to substantial increases in bone density and a 60-70% reduction in vertebral fractures. 

In addition to its role in regulating calcium homeostasis, vitamin D is required for the intestinal absorption of calcium. Synthesis of the intracellular calciumbinding protein, calbindin, required for calcium absorption, is induced by vitamin D, which also affects the permeability of the mucosal cells to calcium, an effect that is rapid and independent of protein synthesis. 

Vitamin D is not strictly a vitamin since it can be synthesized in the skin, and under most conditions that is its major source. Only when sunlight is inadequate is a dietary source required. The main function of vitamin D is in the regulation of calcium absorption and homeostasis most of its actions are mediated by way of nuclear receptors that regulate gene expression. Deficiency—leading to rickets in children and osteomalacia in adults—continues to be a problem in northern latitudes, where sunlight exposure is poor. 

HOLZHERR M L, RETALLACK R W, GUTTERIDGE D H, PRICE R I, FAULKNER D L, WILSON S G, WILL R K, STEWART G O, STUCKEY B G, PRINCE R L, CRIDDLE R A, KENT G N, BHAGAT C I, DHALIWAL S s and JAMROZIK k (2000) Calcium absorption in postmenopausal osteoporosis Benefit of HRT plus calcitriol, but not HRT alone, in both malabsorbers and normal absorbers. Osteoporosis Int 11, 43-51. 

Stimulating activation of vitamin D by 1-a-hydroxylase to cal-citriol (1,25-dihydroxyvitmin D3) to promote calcium absorption in the GI tract and increased calcium mobilization from bone... 

A number of factors can limit calcium absorption, and special consideration must be given to calcium dosing to maximize absorption. Large amounts of calcium taken at once cannot be absorbed. Supplement doses should be limited to 500 to 600 mg of elemental calcium per dose. Calcium intake greater than 2500 mg/day should be avoided due to increased risk of toxicity, including hypercalciuria and hypercalcemia. 

Fullmer CS, Rosen JF. 1990. Effect of dietary calcium and lead status on intestinal calcium absorption. Environ Res 51 91-99. 

Supplemental vitamin D maximizes intestinal calcium absorption and has been shown to increase BMD it may also reduce fractures. 

Might antagonize verapamil Might induce hypercalcemia with thiazide diuretics Fiber laxatives (variable), oxalates, phytates, and sulfates can decrease calcium absorption if given concomitantiy Phenytoin, barbiturates, carbamazepine, rifampin increase vitamin D metabolism... 

Glucocorticoids decrease bone formation through decreased proliferation and differentiation, and enhanced apoptosis of osteoblasts. They also increase bone resorption, decrease calcium absorption, increase renal calcium excretion, and result in secondary hyperparathyroidism. 

Savory et al. 3S) measured calcium and magnesium directly in protein-free filtrates of serum or urine. Baker et al. 36) found that both trichloroacetic acid and hydrochloric acid suppress calcium absorption and that uniform acid content is therefore required for the determination of calcium. Okuda and Sasamoto37) determined calcium by adjusting solution conditions to 20 — 50 % methanol and 650 mg % lanthanum serum is diluted 21-fold and urine is diluted 10—21 fold to bring the calcium concentration into the optimum range of 1 to 0.5 mg %. 

U.S. imports for consumption, 4 528t Calcium(II), concentration formation constant of chelates, 5 717t 12-Calcium-7-aluminate, phase in Portland cement clinker, 5 472t Calcium absorption, 26 292 Calcium addition, in silicon production, 22 505-506... 

Other selective forces may also have been at work. Flatz (1987) has suggested that calcium absorption was a factor in northern Europe. Lactose is known to facilitate calcium absorption in the intestine. The northerly climate frequently prevented skin exposure to sunlight, thereby reducing the body s production of vitamin D. With little vitamin D available, calcium was poorly absorbed and conditions such as rickets could result. The ability to digest lactose would not only allow adults to use an excellent source of calcium, but the lactose would also facilitate its absorption. 

Calcium—Absorption and adsorption— Congresses. 2. Calcium—Metabolism—Congresses. 

PPa digestion were used to correct in vivo extrinsic tag absorption in order to estimate intrinsic food calcium absorption. The corrected extrinsic tag absorption agreed well with the intrinsic tag absorption in rats for all three foods. 

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