Calcium absorption apparent

Calcium retention is dependent on two factors, absorption and excretion. Normal subjects have been observed to have apparent calcium absorptions of 23 (sd = 12) to 27 (sd = 17) percent of the calcium from normal diets (21,22). For 20 women aged 55 to 65 consuming 629 (se = 92) milligrams dietary calcium daily, the apparent absorption was 32.1 (se = 1.9) percent (23). An apparent calcium absorption of 29.5 percent (n = 130) may be calculated from data published by Heaney et al. (15). Apparent absorption values from 29 to 42 percent may be calculated from data published by Linkswiler (24,25). However, much lower apparent absorption values of 6 to 15 percent may also be calculated from data published from the same laboratory (26). Although there is considerable variability in the apparent absorption values determined from many studies, a conservative value of 25 percent seems realistic for normal people consuming typical diets. 

An attempt was made to collate data on human and rat apparent calcium absorption values for several calcium sources. Absorption values were so variable within species and calcium sources that a correlation could not be justified. Much of this variability may be due to methodological differences between the design of the rat and the human experiments. Most of the animal experiments were conducted using rapidly growing rats which were fed modest amounts of calcium but which have high calcium requirements. 

Table I. Comparison of Various Dietary and Physiological Factors on Apparent Calcium Absorption by Rats and Humans...

Effects of the various test fibers in this project on fecal and urine losses of calcium and on calcium balances are given in Table I. Apparent calcium absorptions and calcium balances under these conditions were calculated from this data and are also given in Table I. 

Mean urine and fecal losses of calcium of subjects while receiving the three test fats are shown on Table II. Apparent calcium absorptions and calcium balances were calculated from this data. Mean fecal calcium losses when safflower oil, soybean oil and apricot kernal oil were fed were 460, 500 and 520 mg/day. With a probability of only P<0.10, these difference were not statistically significant although a strong trend toward increased fecal calcium losses with degree of saturatedness of the dietary fat was shown. Thus, a trend toward increase in calcium absorption with more polyunsaturated fats was illustrated. Coupled with changes in... 

As shown in Table III, mean fecal calcium losses tended to be higher when the higher fat diet was fed in comparison to results when the lower fat diet was fed. Therefore, apparent calcium absorption was higher when the low fat diet was fed. These differences were significant at only the P< 0.075 level hence, only a trend was illustrated. In this study no attempt was made to equalize fatty acid proportionality patterns or cholesterol intake. These or other dietary or non-dietary factors may have influenced the observed apparent trends. Other studies with human adults have not demonstrated any apparent influence on level of dietary fat on calcium absorption. 

Ingestion of difructose dianhydride III improves the population and properties of the microorganisms in the intestines, but apparently differently from other oligosaccharides (Saito and Tomita, 2000). Likewise, it improves calcium absorption in the small intestine via a mechanism that appears to differ from other known stimulants. 

Bone Toxicity. In addition to its effect on calcium absorption, excess absorbed strontium adversely affects bone development in several ways, leading to the development of rickets in children and young animals. Strontium binds directly to hydroxyapatite crystals, which may interfere with the normal crystalline structure of bone (Storey 1961). In addition, excess strontium may prevent the normal maturation of chondrocytes in the epiphyseal plates of long bones (Matsumoto 1976). Excess strontium apparently interferes with the mineralization of complexed acidic phospholipids that is thought to help initiate the formation of hydroxyapatite crystals in developing bone (Neufeld and Boskey 1994). As a result, affected bone contains an excess of complexed acidic phospholipid and a significantly lower ash weight. 

Fecal excretion of the macro elements was, on average, 3% for sodium, 19% for potassium, 28% for ash, 36% for phosphorus, 69% for magnesium, and 84% for calcium. The apparent absorption rate is negatively correlated with fecal excretion of the macro elements. The real absorption rate of all these elements is higher than the apparent absorption rate, mainly due to the salivary, biliary and pancreatic excretion of absorbed macro elements into the intestine. 

The apparent absorption rate of the macro elements in humans with a mixed diet varied between 98% for sodium, 83% for potassium, 61% for phosphorus, 35% for magnesium, and 13% for calcium. Ovolacto-vegetarians have a significantly decreased apparent absorption rate for magnesium and calcium, and apparent absorption rates for trace elements varied between 81% for iodine, 62% for selenium, 42% for nickel, 37% for molybdenum, 2.5% for zinc, and 2.0% for manganese. 

SCHONEVILLE JTh, VAtiT Klooster ATH, Diekzwagee a, and Beynen AC (1994) Stimulatory effect of an anion (chloride) -rich ration on apparent calcium absorption in dairy cows. Livestock Prod Sci 40 233-240. 

The availability of mineral elements is commonly high in young animals fed on milk and milk products but declines as the diet changes to solid foods. An additional complication is that the absorption, and hence apparent availability, of some mineral elements is under homeostatic control (determined by the animal s need for them). Iron absorption, discussed in Chapter 8, is the clearest example of this effect, but in ruminants the efficiency of calcium absorption also appears to be dependent on the animal s requirements. 

Calcium Intake Phosphorus Intake Fecal Calcium Apparent Absorption Of Calcium... 

Diet Intake Apparent Absorption Urinary Excretion Calcium Balance... 

Apparent absorption (intake minus fecal excretion) of calcium decreased when the diet contained muffins with added sodium phytate to increase the molar ratio of phytate/calcium from 0.04 to 0.14 and 0.24. One-half of the men excreted more calcium in feces than was consumed when the high phytate diet was consumed. People consuming diets with molar ratios of phytate/calcium exceeding 0.2 may be at risk of calcium deficiency because of low bioavailability of dietary calcium unless physiological adjustments can be accomplished that maintain homeostasis. 

HS-II. The mean (+ SD) daily apparent absorption values were 153+77, 94+65 and 23+66 mg for 0.5, 1.7 and 2.9 g phytate intakes, respectively. There was a significant difference between all means P <0.05, by ANOVA. A plot of apparent absorption of calcium vs the dietary phytate/calcium molar ratio is shown in Figure 1. 

Because phytate intakes were essentially constant, but calcium intake varied with caloric needs, a range of phytate/calcium molar ratios resulted with each phytate level. The correlation coefficient for apparent absorption and dietary phytate/zinc molar ratio was 0.62, P<0.01. The equation of the regression line was y =... 

Apparent absorption of calcium for the six individuals in HS-III is shown in Figure 2. Only one of the six individuals, indicated by stars in Figure 2. tended to be fairly constant in... 

Figure 1. Dietary phytate/calcium molar ratio and apparent absorption of calcium. Each triangle is the mean for one individual for 3 consecutive 5-day menu cyles. See text for study details, HS-II.

Figure 2. Apparent absorption of calcium for 9 consecutive 5-day menu cycles with phytate/calcium molar ratio <0.05, HS-III. Each individual is represented by a different symbol.

For HS-I, with calcium intakes of about 1100 mg/day, no difference was observed in either apparent absorption or balance of calcium over the last 10 of 15 days when the phytate intake was 0.2 or 2.0 g/day. The molar ratio of phytate/calcium was either 0.01 or 0.1 in HS-I. In HS-II the calcium intake was lower, about 740 mg/day, but the same across three levels of phytic acid, 0.5, 1.7 and 2.9 g/day. The phytate/calcium molar ratios were 0.04, 0.14 and 0.24. Apparent absorption of calcium for the 15-day diet treatment period became progressively less as the molar ratio of phytate/calcium increased, to the extent that 6 of 12 individuals excreted more calcium in the feces than they consumed when the mean ratio was 0.24. About 200 mg of calcium was excreted daily in the urine by... 

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. 

Weanling female rats were used as the test model in these studies. They were housed individually (10 rats/diet) and offered diet and deionized water ad libitum for 5 months. Apparent calcium and phosphorus absorption and urinary Ca and P losses were measured on collections made the last five days each month. Urine volume and pH values were also recorded. Other data (growth response, serum Ca and P levels, femur mineral composition, femur strength and density, and femur histology) were obtained at the end of the 5-month feeding study. Details of this and the analytical methods used are presented elsewhere (8). All data were subjected to appropriate statistical analyses. 

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