Balance calcium

The Ca(Il) coaceatratioa ia blood is closely coatroUed aormal values He betweea 2.1 and 2.6 mmol/L (8.5—10.4 mg/dL) of semm (21). The free calcium ion concentration is near 1.2 mmol/L the rest is chelated with blood proteias or, to a lesser extent, with citrate. It is the free Ca(Il) ia the semm that determines the calcium balance with the tissues. The mineral phase of bone is essentially ia chemical equiUbrium with calcium and phosphate ions present ia blood semm, and bone cells can easily promote either the deposition or dissolution of the mineral phase by localized changes ia pH or chelating... 

Oral calcium has long been used for the treatment of osteoporosis, both in the form of dietary and pharmacological supplements. In patients with calcium deficiency, oral calcium at doses of 1000-1500 mg/day corrects a negative calcium balance and suppresses PTH secretion. Sufficient calcium intake is most important for the acciual of peak bone mass in the young, but is also considered the basis of most anti-osteoporotic regimens. In the elderly, supplementation with oral calcium and vitamin D reduces the risk of hip fracture by about 30 4-0%. 

D Calciferol Maintenance of calcium balance enhances intestinal absorption of Ca and mobilizes bone mineral Rickets = poor mineralization of bone osteomalacia = bone demineralization... 

DRAPER c R, DICK I M and PRINCE R L (1999) The effect of estrogen deficiency on calcium balance in mature rats. Calcif Tissue Int 64, 325-8. 

Among the oldest women with impaired calcium balance a high caffeine intake may predispose to cortical bone loss. However, effects were age and site specific and after... 

Heany, R. P., Recker, R. R., Effects of nitrogen, phosphorus, and caffeine on calcium balance in women, Journal of Laboratory Clinical Medicine, 99, 46, 1982. 

Although the kidneys are not considered endocrine glands per se, they are involved in hormone production. Erythropoietin is a peptide hormone that stimulates red blood cell production in bone marrow. Its primary source is the kidneys. Erythropoietin is secreted in response to renal hypoxia. Chronic renal disease may impair the secretion of erythropoietin, leading to development of anemia. The kidneys also produce enzymes. The enzyme renin is part of the renin-angiotensin-aldosterone system. As will be discussed, these substances play an important role in the regulation of plasma volume and therefore blood pressure. Other renal enzymes are needed for the conversion of vitamin D into its active form, 1,25-d i hyd ro xyv itamin D3, which is involved with calcium balance. 

Calcium-phosphorus balance is mediated through a complex interplay of hormones and their effects on bone, GI tract, kidney, and parathyroid gland. As kidney disease progresses, renal activation of vitamin D is impaired, which reduces gut absorption of calcium. Low blood calcium concentration stimulates secretion of parathyroid hormone (PTH). As renal function declines, serum calcium balance can be maintained only at the expense of increased bone resorption, ultimately resulting in renal osteodystrophy (ROD) (Fig. 76-7). 

Metabolic Balance Methods. Theoretically, the amount of mineral retained in the body should be determinable by balance methods. Heroux and Peter (50) attempted to do this for calcium and magnesium in rats fed three diets. For rats fed their stock diet, they predicted from balance data that the carcasses would contain 23.8 g calcium and 605 mg magnesium. By analysis, the carcasses contained 4.45 g calcium and 152 mg magnesium. However, the relationship between calcium balance data (X) and carcass data (Y) were closely related (Y = 1.05X -. 03, r = 0.99 for group mean data) in the rat data of Whittemore et al. (51). 

Diet Intake Apparent Absorption Urinary Excretion Calcium Balance... 

All subjects were in negative calcium balance when consuming the basal low calcium, low phosphorus diet (Table VII), the mean calcium loss being 110 mg/day. The orthophosphate supplement significantly reduced this loss to 29 mg/day, due to decreases in both urinary and fecal calcium losses. The polyphosphate supplement, however, caused... 

Two metabolic balance studies were conducted using healthy adult men to study the effect of phytate on bioavailability of dietary calcium. Dietary treatments were each 15 days in duration. In the first study, a mean daily calcium balance of 208+58 (SD) mg was observed when 2.0 g of phytate from 36 g of whole wheat bran was consumed daily with 1100 mg of calcium, phytate/calcium molar ratio 0.11. Calcium balance was 184+87 mg when 36 g of dephytinized bran was consumed with the same intake of calcium, phytate/calcium molar ratio 0.01. In the second study, calcium intake was 740 mg/day. 

The brown or whole meal bread diets employed by previous investigators were often variable in calcium and phytate intakes, not only between individuals, but by the same individual subjected to different diet treatments. Nevertheless an estimate of the molar ratio of phytate/calcium in the brown or whole meal bread diets used by McCance and Widdowson (UO), Walker et al. (11) and Reinhold et al. (2, 12) is 0.25 or greater. These investigators observed either negative or less positive calcium balance and apparent absorption when the brown bread diets were consumed compared to white bread diets with phytate/calcium molar ratios less than 0.05. Our results support their findings. Reinhold et al. (2) and McCance and Widdowson (33) used sodium phytate in some studies as well as whole wheat bread and observed similar results. 

Our studies do not resolve the question of phytate vs fiber for the effect of wheat bran on dietary calcium bioavailability. Phytate level clearly affected apparent absorption of calcium in HS-II in the presence of an amount of the water insoluble fraction of dephytinized bran equivalent to 12 g of untreated bran and the phytate supplied as sodium phytate. An additional trial using untreated bran and the same amount of fiber as the water insoluble fraction with sodium phytate could resolve the question of fiber vs phytate. In HS-I, the balances were positive when a relatively large amount of bran, 36 g/day, was consumed. Calcium intakes were possibly higher than most men consume, but under the dietary conditions imposed for 15 days, the phytate and fiber of 36 g of bran did not express an adverse effect on calcium balance. 

High intakes of protein, particularly animal protein coupled with low phosphorus intakes have been credited as resulting in high urinary losses of calcium and poor calcium balances which can be overcome by increasing intakes of either calcium or phosphorus or lowering protein intake in the adult human (9,15,16). In the present study, not only did the animal protein diet result in bones more resistant to breakage than did the plant protein diet, but the animal protein fed animals were seemingly less affected by variations in intake of phosphorus and calcium than were the plant protein fed animals. 

Review of studies on the effect of oxalic acid on calcium bioavailability in rats and in humans indicates that most of the research was done between 1930 and 1950. Decreased availability of calcium in young rats was reported when spinach containing oxalic acid was fed with low calcium diets. The extent of the effect of oxalic acid on calcium availability was shown to be related to levels of calcium and oxalic acid, as well as the presence of vitamin D in the diet. In human studies there was generally no effect of oxalic acid on calcium balance however, in a few studies decreased calcium balances were reported. There is recent evidence that oxalic acid consumed along with a moderately high level of fiber intake may have adverse effects on calcium balance of human subjects. 

Mean 3-day calcium balances, determined for from 2-5 periods, were positive for all diets, but were lower on the diets containing carrots and spinach. The authors concluded that children do not utilize calcium from vegetables as well as that from milk. 

McLaughlin (25) reported that although calcium balances for seven women were somewhat lower during 6 days in which spinach replaced milk in the diet, all balances were positive. The women were fed diets containing about 500 mg of calcium/day in which 79% came from milk for 6 days and 73% came from spinach (about 276 g/day) for 6 days. The spinach diet contained 2.0 g oxalic acid/day. The calcium excretion in urine was 2-3 times greater during the milk period. 

Schultz et al. (26) found that feeding spinach to four infants for 3-6 days did not affect calcium balance, with the possible exception of a slight lowering when dried spinach was fed. Infants 5 weeks-6 months of age were fed only milk formula for a 6-day control period. The spinach was added to the formula diet in the following amounts 6 g dried spinach, 60 g pureed spinach, or 70 g raw spinach per day. The infants were also given cellulose in amounts of 6 or 9 g/day. There was generally a larger output of feces when the diet contained spinach. 

In two women studied by Fincke and Garrison (28), the calcium of kale was better utilized than that of spinach, when the vegetables supplied 80-86% of the calcium in the diet. One diet contained kale and two diets contained spinach (about 500 g) calcium intakes were 400, 304, and 445 mg/day, respectively. Two 3-day balances were determined after 3 days on each diet. Calcium balances were negative on all diets, but were more negative when the spinach was consumed. 

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