Calcium iron absorption affected

Phosphates are important because they affect the absorption of calcium and other elements. The absorption of inorganic phosphorus depends on the amount of calcium, iron, strontium, and aluminum present in the diet. Chapman and Pugsley (1971) have suggested that a diet containing more phosphorus than calcium is as detrimental as a simple calcium deficiency. The ratio of calcium to phosphorus in bone is 2 to 1. It has been recommended that in early infancy, the ratio should be 1.5 to 1 in older infants, 1.2 to 1 and for adults, 1 to 1. The estimated annual per capita intake in the United States is 1 g Ca and 2.9 g P, thus giving a ratio of 0.35. The danger in raising phosphorus levels is that calcium may become unavailable. 

The direct measurement in the diet of substances known to adversely affect zinc absorption. This most commonly would require determination of the phytic acid content. Substances such as dietary fibre, calcium, iron, tin, oxalate and others, are also important in certain instances. 

Many factors that affect calcium absorption have a similar effect on the absorption of iron. Absorption is promoted by ascorbic acid possibly because it reduces ferric to ferrous iron. Absorption is augmented in iron deficiency and depressed when stores are increased. Thus when, after a haemorrhage, erthyropoiesis is accelerated, iron absorption is enhanced and, under conditions in which erythropoiesis is reduced, e.g. starvation or descent from a high altitude, absorption is reduced. 

The absorption of tetracycline administered orally is variable and depend upon the type of tetracycline used. The tetracycline form insoluble complexes i.e. chelation with calcium, magnesium, milk and antacids reduce their absorption. Administration of iron also interferes with the absorption of tetracycline. Doxycycline is rapidly and virtually completely absorbed after oral administration and its absorption is not affected by presence of food or milk. 

The administration of tetracycline with food can ameliorate its irritative effects, bnt food can adversely affect the drug s absorption. In contrast, the absorption of doxycycline is only slightly affected by the presence of food, including dairy prodncts. Becanse all tetracyclines can form complexes with divalent cations, the absorption of any tetracycline is markedly decreased when administered with iron-containing tonics or antacids containing calcium, magnesium, or aluminum. Sodium bicarbonate also adversely affects tetracycline absorption. 

Interactions among minerals affecting their utilization are currently an area of intense investigation. Greger has reviewed impacts of phosphorus and calcium on iron utilization in this book. Interactions of iron with copper and zinc have also been established (14-16). If minerals compete with iron for absorption binding sites, adverse effects on iron bioavailability may occur. 

Lead absorption is heavily influenced by food intake much higher rates occur after fasting than when lead is ingested with a meal. This effect may be due mainly to competition from other ions, particularly iron and calcium, for intestinal transport pathways. Absorption is also affected by age the typical absorption rates in adults and infants are 5-10% and about 50%, respectively. 

Loss of gastric acidity from chronic proton pump inhibitor treatment may affect the bioavailability of such drugs as ketoconazole, ampicillin esters, and iron salts. Chronic therapy, with proton pump inhibitors has been linked to increased frequency of hip fractures, possibly secondary to decreased absorption of calcium. 

The results of dietary zinc analysis need to be considered in terms of the availability of the zinc in the food for intestinal absorption. The zinc content of whole meals and the total daily zinc intake are not sufficient information on their own, without knowledge of factors which inhibit or promote intestinal absorption (O Dell, 1984). Free ionic zinc probably does not exist in the intestinal tract, zinc being bound to molecular species such as protein, amino acids, phytic acid, citrate and others. The bioavailability of the metal is determined by the nature of these zinc binding ligands. When the zinc complex is insolubie as in Zn-phytate, the uptake from diet is poor, whereas zinc-protein or zinc-amino acid complexes are more easily dissociated and are a good source of available zinc. Other dietary components affect zinc absorption such as the amount of iron, calcium and phosphate. 

The major sources of lead for infants and children are dust and soil, chips of lead paint, water and food (Lockitch, 1993). According to the US EPA in 2-year-old infants the intake of lead is 47% from food, 1% from air, 45% from dust, 6% from water and 1% from soil. Deficit of calcium, phosphate, selenium or zinc may result in increased lead absorption. Iron and vitamin D also affect absorption of lead (WHO, 1995). 

Metals and metal compounds taken up orally are mainly absorbed in the intestinal tract. It is assumed that absorption mainly occurs by means of diffusion processes following the concentrations gradients. In addition, there exist special transport mechanisms for certain essential metal ions like iron or calcium. Active transport, in which movements occur against an increasing concentration gradient by means of metabolic energy, is effective for sodium and potassium ions. The rate of absorption is affected by the chemical form in which the metal occurs (species) and by a number of dietary and constitutional factors. 

The absorption of calcium, sodium, potassium, chloride, magnesium, and iron is thought to be influenced by the thyroid hormone. The results of the studies of the effect of thyroxine on electrolyte metabolism are often contradictory and difficult to interpret however, it seems accepted that thyroxine affects phosphorus metabolism by increasing the excretion of the metal in both urine and stools. 

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