Bones, human phosphorus

Phosphorus. Eighty-five percent of the phosphoms, the second most abundant element in the human body, is located in bones and teeth (24,35). Whereas there is constant exchange of calcium and phosphoms between bones and blood, there is very Httle turnover in teeth (25). The Ca P ratio in bones is constant at about 2 1. Every tissue and cell contains phosphoms, generally as a salt or ester of mono-, di-, or tribasic phosphoric acid, as phosphoHpids, or as phosphorylated sugars (24). Phosphoms is involved in a large number and wide variety of metaboHc functions. Examples are carbohydrate metaboHsm (36,37), adenosine triphosphate (ATP) from fatty acid metaboHsm (38), and oxidative phosphorylation (36,39). Common food sources rich in phosphoms are Hsted in Table 5 (see also Phosphorus compounds). 

Milk is an excellent source of calcium, phosphorus, riboflavin (vitamin B2), thiamine (vitamin Bl) and vitamin B12, and a valuable source of folate, niacin, magnesium and zinc (Food Standards Agency, 2002). In particular, dairy products are an important source of calcium, which is vital for maintaining optimal bone health in humans (Prentice, 2004). The vitamins and minerals it provides are all bioavailable (i.e. available for absorption and use by the body) and thus milk consumption in humans increases the chances of achieving nutritional recommendations for daily vitamins and mineral intake (Bellew et al., 2000). 

Calcitonin is a polypeptide hormone that (along with PTH and the vitamin D derivative, 1,25-dihydroxycholecalciferol) plays a central role in regulating serum ionized calcium (Ca2+) and inorganic phosphate (Pi) levels. The adult human body contains up to 2 kg of calcium, of which 98 per cent is present in the skeleton (i.e. bone). Up to 85 per cent of the 1 kg of phosphorus present in the body is also found in the skeleton (the so-called mineral fraction of bone is largely composed of Ca3(P04)2, which acts as a body reservoir for both calcium and phosphorus). Calcium concentrations in human serum approximate to 0.1 mg ml-1 and are regulated very tightly (serum phosphate levels are more variable). 

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. 

In a recent study involving the inorganic analysis of human ribs from 10 subjects,66 it has been found that the calcium content varied from 24.12 to 26.91 per cent, the phosphorus from 10.75 to 12.11 per cent, and the carbonate as carbon dioxide varied from 2.81 to 3.95 per cent. Inter-individual differences of this magnitude would seem to exist since the inorganic composition of bone is probably relatively stable and not subject to short-term fluctuations. 

Phosphorus is important in human biochemistry, mainly as phosphate. Phosphate is an important component of bone. 

Martini and Wood (2002) tested the bioavailability of 3 different sources of Ca in 12 healthy elderly subjects (9 women and 3 men of mean SEM age 70 3 and 76 6 years, respectively) in a 6-week crossover trial conducted in a Human Study Unit. Each Ca source supplied 1000 mg Ca/day and was ingested for 1 week with meals (as 500 mg Ca 2x/day), thus contributing to a high-Ca intake (1300 mg Ca/day). A low-Ca intake (300 mg Ca/day strictly from the basal diet) was adhered to for 1 week in-between each treatment. The Ca sources included skim milk, CCM-fortified OJ, and a dietary supplement of CaCOa. Assessment parameters were indirect measures predicted to reflect the relative bioavailability of Ca postprandially via an acute PTH suppression test (hourly for 4h). Longer-term responses to Ca supplementation were assessed via a number of urinary and serum hormone, mineral, and bone resorption biomarkers (i.e., vitamin D, Ca, phosphorus, and collagen t) e 1 N-telopeptide cross-links). 

Cerium in Plants and Animals. Professor Alfonso Cossa, finding the rare earths of the ceria series to be present in many apatites, and realizing the close association in nature between these earths and calcium and phosphorus, tested for them and detected their presence in bone (66). He also detected them in the ash of barley, beech wood, and tobacco. With the aid of C. Schiapparelli and G. Peroni of the University of Turin, he demonstrated their presence in human urine (66, 67, 68). 

About 98% of the 1.5 kg of calcium and 85% of the 1 kg of phosphorus in the human adult are found in bone. Bone is composed of two distinct tissue structures cortical... 

Calcium and phosphate, the major mineral constituents of bone, are also two of the most important minerals for general cellular function. Accordingly, the body has evolved a complex set of mechanisms by which calcium and phosphate homeostasis are carefully maintained (Figure 42-1). Approximately 98% of the 1-2 kg of calcium and 85% of the 1 kg of phosphorus in the human adult are found in bone, the principal reservoir for these minerals. These functions are dynamic, with constant remodeling of bone and ready exchange of bone mineral with that in the extracellular fluid. Bone also serves as the principal structural support for the body and provides the space for hematopoiesis. Thus, abnormalities in bone mineral homeostasis can lead not only to a wide variety of cellular dysfunctions (eg, tetany, coma, muscle weakness) but also to disturbances in structural support of the body (eg, osteoporosis with fractures) and loss of hematopoietic capacity (eg, infantile osteopetrosis). 

A potential concern has been the dietary ratio of calcium to phosphorus (Ca P) in relation to bone health. Based on data from animal studies and on the relative calcium content in bone, a dietary Ca P ratio of 1 1 to 2 1 is recommended as beneficial for bone mineralization in humans (NAS 1980A Chinn 1981 Linkswiler and Zemel 1979). The Ca P ratio in cow s milk (1.3 1) closely approximates that found in bones. The average American diet is estimated to contain a Ca P ratio of 1 1.6 (Chinn 1981 Greger and Krystofiak 1982) to 1 3 (Linkswiler and Zemel 1979), and if no dairy foods are consumed, it may be as low as 1 4. 

There is some evidence, mostly from animal studies, to suggest that high dietary levels of phosphorus, especially if dietary levels of calcium are low, may adversely affect bone mass and calcium metabolism (Greger and Krystofiak 1982). However, in humans there is little direct evidence to indicate that large variations in dietary phosphorus or in the Ca P ratio have any significant influence on calcium utilization or balance (Heaney et al. 1982). Some preliminary findings, however, suggest that the form of phosphorus may influence calcium absorption (Zemel et al. 1982). Hexametaphosphate, as compared with orthophos-... 

The many diverse components of milk have demonstrable effects on human health. Perhaps, the most commonly associated component of dairy food is that of dietary calcium. Dairy products provide the most significant contribution to dietary calcium intake in the modem Western diet. It has been estimated that dairy products contribute to >72% of dietary calcium in the United States (Huth et al., 2006). Calcium is an important mineral for maintenance of optimal bone health (Bonjour et al., 2009) and is an integral component of key metabolic pathways relating to, for example, muscle contraction both in skeletal and smooth muscle (Cheng and Lederer, 2008). Further, dairy products contribute other essential nutrients in the diet, such as proteins, phosphorus, potassium, zinc, magnesium, selenium, folate, riboflavin, vitamin B12, and vitamin A (Haug et al., 2007 Huth et al., 2006). Low-fat milk alternatives are fortified with vitamin A and vitamin D which is added to milk and fermented milk in many countries making it an important source for vitamin D (Huth et al., 2006). 

Humans occupationally exposed to phosphorus probably ingested some airborne white phosphorus. In a study of 71 humans occupationally exposed to fumes/vapors and paste containing white phosphorus, oral exposure to phosphorus passed from hand to mouth was likely, because the workers constantly handled a paste containing 4-6% white phosphorus, and washroom facilities at the plants were inadequate (Ward 1928). White phosphorus-related deaths occurred in 0 of 44 and 2 of 27 of the workers exposed for intermediate and chronic durations, respectively. In the two cases of death, the workers died from complications related to phossy jaw, a degenerative condition affecting the soft tissue, bones, and teeth of the oral cavity. In this condition, the toxic effects of white phosphorus probably result from the local irritant action of white phosphorus on tissues in the mouth. Thus, white phosphorus paste passed from hand to mouth and the local action of airborne white phosphorus on the oral cavity may have contributed to the development of phossy jaw, and subsequent death, of these two workers. It is not known whether white phosphorus ingested and absorbed into the systemic circulation contributed to the development of phossy jaw in the two workers that died (Ward 1928). Details of this study are provided in Section 2.2.2.2. 

The human organism contains 1-1.4 kg calcium, and about 1% of this is in the extracellular fluid. The rest is largely in bone. The serum calcium concentration is 9-11.5 mg/dL, of which 4.5-5.0 mg/dL is in the free, ionized, biologically active form. The rest is protein bound or complexed with a variety of chelators, such as citrate. The daily dietary calcium requirement is 400-500 mg, and each day, 300-400 mg calcium is lost in the urine and an additional 150 mg in the feces. Inorganic phosphorus (largely as HP042 ) amounts to 2.7-4.5 mg/dL in adult serum. 

Phosphorus is an essential nutrient for life on Earth. Plants need phosphorus, along with other nutrients, in order to grow. Phosphorus is a component of bones and teeth. In addition, phosphorus is excreted as waste from the body. Thus, it is present in human sewage. 

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