Dietary perturbation of calcium metabolism in normal man: compartmental analysis

Biological Activities of Lactose-Based Prebiotics and Symbiosis with Probiotics on Controlling Osteoporosis, Blood-Lipid and Glucose Levels

Lactose-based prebiotics are synthesized by enzymatic- or microbial- biotransformation of lactose and have unique functional values. In this comprehensive review article, the biochemical mechanisms of controlling osteoporosis, blood-lipid, and glucose levels by lactose-based prebiotics and symbiosis with probiotics are reported along with the results of clinical investigations. Interaction between lactose-based prebiotics and probiotics reduces osteoporosis by (a) transforming insoluble inorganic salts to soluble and increasing their absorption to gut wall; (b) maintaining and protecting mineral absorption surface in the intestine; (c) increasing the expression of calcium-binding proteins in the gut wall; (d) remodeling osteoclasts and osteoblasts formation; (e) releasing bone modulating factors; and (f) degrading mineral complexing phytic acid. Lactose-based prebiotics with probiotics control lipid level in the bloodstream and tissue by (a) suppressing the expressions of lipogenic- genes and enzymes; (b) oxidizing fatty acids in muscle, liver, and adipose tissue; (c) binding cholesterol with cell membrane of probiotics and subsequent assimilation by probiotics; (d) enzymatic-transformations of bile acids; and (e) converting cholesterol to coprostanol and its defecation. Symbiosis of lactose-based prebiotics with probiotics affect plasma glucose level by (a) increasing the synthesis of gut hormones plasma peptide-YY, glucagon-like peptide-1 and glucagon-like peptide-2 from entero-endocrine L-cells; (b) altering glucose assimilation and metabolism; (c) suppressing systematic inflammation; (d) reducing oxidative stress; and (e) producing amino acids. Clinical investigations show that lactose-based prebiotic galacto-oligosaccharide improves mineral absorption and reduces hyperlipidemia. Another lactose-based prebiotic, lactulose, improves mineral absorption, and reduces hyperlipidemia and hyperglycemia. It is expected that this review article will be of benefit to food technologists and medical practitioners.

Compensatory Changes in Calcium Metabolism Accompany the Loss of Vitamin D Receptor (VDR) From the Distal Intestine and Kidney of Mice

1,25 Dihydroxyvitamin D3 (1,25(OH)2 D) increases intestinal Ca absorption when dietary Ca intake is low by inducing gene expression through the vitamin D receptor (VDR). 1,25(OH)2 D-regulated Ca absorption has been studied extensively in the small intestine, but VDR is also present in the large intestine. Our goal was to determine the impact of large intestinal VDR deletion on Ca and bone metabolism. We used transgenic mice expressing Cre-recombinase driven by the 9.5-kb human caudal type homeobox 2 (CDX2) promoter to delete floxed VDR alleles from the caudal region of the mouse (CDX2-KO). Weanling CDX2-KO mice and control littermates were fed low (0.25%) or normal (0.5%) Ca diets for 7 weeks. Serum and urinary Ca, vitamin D metabolites, bone parameters, and gene expression were analyzed. Loss of the VDR in CDX2-KO was confirmed in colon and kidney. Unexpectedly, CDX2-KO had lower serum PTH (-65% of controls, p < 0.001) but normal serum 1,25(OH)2 D and Ca levels. Despite elevated urinary Ca loss (eightfold higher in CDX2-KO) and reduced colonic target genes TRPV6 (-90%) and CaBPD9k (-80%) mRNA levels, CDX2-KO mice had only modestly lower femoral bone density. Interestingly, duodenal TRPV6 and CaBPD9k mRNA expression was fourfold and threefold higher, respectively, and there was a trend toward increased duodenal Ca absorption (+19%, p = 0.076) in the CDX2-KO mice. The major finding of this study is that large intestine VDR significantly contributes to whole-body Ca metabolism but that duodenal compensation may prevent the consequences of VDR deletion from large intestine and kidney in growing mice.

Diet, gut microbiome, and bone health

Interactions between the environment, the gut microbiome, and host characteristics that influence bone health are beginning to be explored. This is the first area where functional benefits from diet-induced changes in the gut microbiome have been reported for healthy people. Several prebiotics that reach the lower intestine have resulted in an altered gut microbiome that is thought to enhance fermentation of the fibers to produce short-chain fatty acids. These changes are positively correlated with increases in fractional calcium absorption in adolescents and with increases in measures of bone density and strength in animal models. New methodologies are available to explore mechanisms and to refine intervention strategies.

Prospective studies of total and ionized serum calcium in relation to incident and fatal ovarian cancer

OBJECTIVE

Biological markers that could aid in the detection of ovarian cancer are urgently needed. Many ovarian cancers express parathyroid hormone-related protein, which acts to raise calcium levels in serum. Thus, we hypothesized that high serum calcium levels might predict ovarian cancer.

METHODS

We examined the associations between total and ionized serum calcium and ovarian cancer mortality in the Third National Health and Nutrition Survey (NHANES III) using Cox proportional hazard models. We then examined the associations of serum calcium with incident ovarian cancer in a second prospective cohort, the NHANES Epidemiological Follow-up Study (NHEFS).

RESULTS

There were eleven deaths from ovarian cancer over 95,556 person-years of follow-up in NHANES III. After multivariable adjustment, the risk for fatal ovarian cancer was 52% higher for each 0.1 mmol/L increase in total serum calcium (RH=1.52, 95% CI 1.06-2.19) and 144% higher for each 0.1 mmol/L increase in ionized serum calcium (RH=2.44, 95% CI=1.45-4.09). Associations persisted after adjusting for nulliparity and the use of oral contraceptives. Eight incident ovarian cancers occurred over 31,089 person-years of follow-up in the NHEFS. After adjusting for covariates, there was a 63% higher risk for ovarian cancer with each 0.1 mmol/L increase in total serum calcium (95% CI 1.14-2.34). Similar results were observed for albumin-adjusted serum calcium.

CONCLUSIONS

Higher serum calcium may be a biomarker of ovarian cancer. This is the first report of prospective positive associations between indices of calcium in serum and ovarian cancer. Our findings require confirmation in other cohorts.

Calcium balance in normal individuals and in patients with chronic kidney disease on low- and high-calcium diets

Calcium balance in chronic kidney disease is poorly understood since its deficiency is a stimulus for secondary hyperparathyroidism and consequent bone loss while calcium excess promotes extra-osseous calcifications. To help resolve this, we evaluated calcium balance in normal individuals and in patients with chronic kidney disease (CKD) on daily diets containing 800 and 2000 mg elemental calcium. Both normal individuals and patients with late stage 3 and stage 4 CKD were in slightly negative to neutral calcium balance on the 800 mg calcium diet. Normal individuals were in modest positive calcium balance on the 2000 mg diet while patients with CKD on the same diet were in marked positive calcium balance at least over the 9 days of study; and significantly greater than the normal individuals. Increased calcium intake significantly decreased 1,25 dihydroxy-vitamin D and intact parathyroid hormone levels but did not alter the serum calcium concentration. Thus, our finding have important implications for both preventing calcium deficiency and loading in individuals with late stage 3 and stage 4 CKD.

Calcium requirements: new estimations for men and women by cross-sectional statistical analyses of calcium balance data from metabolic studies

BACKGROUND

Low intakes of calcium are associated with an increased risk of both osteoporosis and cardiovascular disease.

OBJECTIVE

To provide new estimates of the average calcium requirement for men and women, we determined the dietary calcium intake required to maintain neutral calcium balance.

DESIGN

Calcium balance data [calcium intake -(fecal calcium + urinary calcium)] were collected from 155 subjects [women: n = 73; weight: 77.1 +/- 18.5 kg; age: 47.0 +/- 18.5 y (range: 20-75 y); men: n = 82; weight: 76.6 +/- 12.5 kg; age: 28.2 +/- 7.7 y (range: 19-64 y)] who participated in 19 feeding studies conducted in a metabolic unit. Balance data from the final 6-12 d of each dietary period (minimum length:18 d) of each study (1-9 observations per subject) were analyzed. Data were excluded if individual intakes of magnesium, copper, iron, phosphorus, or zinc fell below the estimated average requirements or exceeded the 99 th percentile of usual intakes from the 1994 Continuing Survey of Food Intakes by Individuals (for iron, above the upper limit). Daily intakes of calcium ranged between 415 and 1740 mg. The relation between intake and output was examined by fitting random coefficient models. Coefficients were included to test for sex and age differences.

RESULTS

The models predicted a neutral calcium balance [defined as calcium output (Y) equal to calcium intake (C)] at intakes of 741 mg/d [95% prediction interval (PI): 507, 1035; Y = 148.29 + 0.80C], 9.4 mg kg body wt(-1) d(-1) [95% PI: 6.4, 12.9; Y = 1.44 + 0.85C], or 0.28 mg kcal(-1) d(-1) [95% PI: 0.19, 0.38; Y = 0.051 + 0.816C]. Neither age nor sex affected the estimates when calcium intakes were expressed as mg/d or as mg kg body wt(-1) d(-1).

CONCLUSION

The findings suggest that the calcium requirement for men and women is lower than previously estimated.

H-tetracycline as a proxy for Ca for measuring dietary perturbations of bone resorption

Our group is interested in evaluating early effects of dietary interventions on bone loss. Postmenopausal women lose bone following reduction in estrogen which leads to increased risk of fracture. Traditional means of monitoring bone loss and effectiveness of treatments include changes in bone density, which takes 6 months to years to observe effects, and changes in biochemical markers of bone turnover, which are highly variable and lack specificity. Prelabeling bone with (41)Ca and measuring urinary (41)Ca excretion with accelerator mass spectrometry provides a sensitive, specific, and rapid approach to evaluating effectiveness of treatment. To better understand (41)Ca technology as a tool for measuring effective treatments on reducing bone resorption, we perturbed bone resorption by manipulating dietary calcium in rats. We used (3)H-tetracycline ((3)H-TC) as a proxy for (41)Ca and found that a single dose is feasible to study bone resorption. Suppression of bone resorption, as measured by urinary (3)H-TC, by dietary calcium was observed in rats stabilized after ovariectomy, but not in recently ovariectomized rats.

Pathophysiology of osteoporosis

As with many chronic diseases that express themselves late in life, osteoporosis is distinctly multifactorial, both in etiology and pathophysiology. Osteoporotic fractures occur because of a combination of injury and intrinsic bony fragility. Injury comes most often from a combination of falls, falling to the side, poor postural reflexes that fail to protect bony parts from impact, and reduced soft-tissue padding over bony prominences. The bony fragility itself is a composite of geometry, low mass density, severance of microarchitectural connections in trabecular structures, and altered bone material quality. The latter is primarily the result of accumulated fatigue damage, but reduced collagen cross-links and other intrinsic material defects may play a role as well. Reduced bone mass, in turn, is the result of varying combinations of gonadal hormone deficiency, inadequate intakes of calcium and vitamin D, decreased physical activity, comorbidity, and the effects of drugs used to treat various unrelated medical conditions. Finally, the often poor outcome from hip fracture in the elderly is partly due to associated protein-calorie malnutrition. An adequate preventive program for osteoporotic fracture must address as many of these factors as possible and be as multifaceted as the disease is multifactorial.

Pathophysiology of osteoporosis

As with many chronic diseases that express themselves late in life, osteoporosis is distinctly multifactorial both in etiology and in pathophysiology. Osteoporotic fractures occur because of a combination of injury and intrinsic bony fragility. The injury comes most often from a combination of falls, poor postural reflexes that fail to protect bony parts from impact, and reduced soft tissue padding over bony prominences. The bony fragility itself is a composite of geometry, low mass density, severance of microarchitectural connections in trabecular structures, and accumulated fatigue damage. Reduced bone mass, in turn, is caused by varying combinations of gonadal hormone deficiency, inadequate intakes of calcium and vitamin D, decreased physical activity, comorbidity, and the effects of drugs used to treat various unrelated medical conditions. Finally, the often poor outcome from hip fracture in the elderly is partly caused by associated protein-calorie malnutrition. An adequate preventive program for osteoporotic fracture must address as many of these factors as possible, ie, it must be as multifaceted as the disease is multifactorial.

Milk consumption decreases activity of human serum alkaline phosphatase: a cross-sectional study

Since the Japanese have not reached the recommended daily allowance (RDA) for calcium (600 mg), milk is recommended as a Ca-rich food to increase Ca intake and prevent osteoporosis in Japan. To determine whether milk consumption influences Ca/bone metabolism in the Ca-deficient population, relationships between milk consumption and serum alkaline phosphatase (Al-P) activity were analyzed in 3,098 premenopausal and 1,182 postmenopausal women and 13,141 men aged 30 to 69 years. Milk consumption was classified into no/yes groups by a self-administered questionnaire that asked "Do you drink a glass of milk (180 to 200 mL) or more everyday?". Regardless of age or sex, the "yes" group had a lower activity of serum Al-P than the "no" group. Milk consumption decreased the activity to a greater degree in women, especially perimenopausal/postmenopausal women, than in men. These results were confirmed in a multivariate analysis considering age, body mass index (BMI), and smoking and drinking habits as confounding factors. Although menopause obviously increased serum Al-P activity in perimenopausal women, it could not influence the effects of milk consumption on the activity. These results suggest that milk has osteostatic effects on humans via a mechanism different from that of estrogens. Milk consumption, even one glass per day, may be an easy and effective strategy for prevention of osteoporosis in the Ca-deficient population, especially perimenopausal/postmenopausal women.

The bone-remodeling transient: implications for the interpretation of clinical studies of bone mass change

A computer simulation of the bone-remodeling transient is described, in which the focus is explicitly on changes in clinically measurable bone mass (or density). Based upon quantitative remodeling data accumulated by histomorphometry and calcium tracer kinetics, the simulation shows that much of the apparent gain in bone produced by several agents currently employed to treat osteoporosis can be explained as a remodeling transient rather than as a fundamental alteration of remodeling balance. Even gains as large as 30% or more can be produced by nothing more than the remodeling transient under certain plausible combinations of basal remodeling rate, remodeling period, and degree of bone loss. The simulation further highlights the importance, in evaluating bone-active agents, of separating the response across the first remodeling period from bone changes that may ensue thereafter.

Modeling human calcium tracer kinetics using a minimum of assumptions

A conceptually simple model of human calcium kinetics, based on the Bauer-Carlsson-Linquist (B.C.L.) expression, is presented. The B.C.L. model assumes tracer retention in the body, occurs either in an exchangeable pool or in the skeleton, and the rate of calcium transfer from pool to bone (mineralization) is constant. As a modification, it is demonstrated that the existence of an expanding calcium pool and its rate of expansion may be directly determined from the raw data, without a priori assumptions. If data on whole body retention are unavailable, the concept of dermal tracer loss as the difference between tracer excretion and whole body retention may be used to estimate whole body retention. It has been possible to compare the modified B.C.L. expression with various multicompartmental kinetic models by analyzing raw data supplied by other workers and making comparisons with their published results. As methodologies are very different, the two sets of estimates of bone mineralization rate and exchangeable pool size have been ranked within individual groups. In five of six comparisons, the results indicate a rank correlation coefficient with a p-value better than 0.05 occurred. In all cases of data analysis from "normal" subjects, the calcium pool was found to be expanding. The existence of an expanding pool renders the model similar to a previous one, but the present one is conceptually and mathematically simpler in achieving equivalent results.

Effect of calcium and phosphorus on the gastrointestinal absorption of 203Pb in man

Calcium and phosphorus were mainly responsible for reducing the gastrointestinal absorption of lead in human subjects. The effect of calcium was greater than phosphorus, and their combined effect was more than additive. Increasing weights of calcium and phosphorus progressively reduced lead absorption. The relationship between absorption and increasing weights could be described by two negative exponentials. These effects could be explained if lead competed with calcium and phosphorus for common transport mechanisms in the gut. Milk was also found to reduce lead absorption. Adding milk to the diet of people with low dietary calcium intake could reduce the possibility of increased absorption of ingested lead.

Effects of oral zinc loading on zinc metabolism in humans II: in vivo kinetics

The effects of oral zinc loading on zinc metabolism were studied in 10 patients with taste and smell dysfunction following oral administration of Zn-65 (physical t1/2 = 245 d) and subsequent administration of oral stable zinc. Patients took an ad libitum dietary zinc intake of 8-13 mg daily for 290-440 days (mean, 336) following Zn-65 administration, followed by an intake of an additional 100 mg/day of zinc ion (as ZnSO4) over the next 112-440 days (mean, 307). A previously developed compartmental model, based on five day studies of patients with taste and smell dysfunction, was extended in such a way that it was consistent with both short term and long term kinetics. In this extended model, the turnover of 90% of total body zinc, previously unaccounted for by the kinetics in the short term studies could be explained by a single compartment, as postulated in the short term studies. Using the model, it was found that changes in the rate constants for gastrointestinal absorption and renal excretion of zinc were both necessary and sufficient to explain the changes seen in the kinetic curves following oral zinc loading. Michaelis-Menten type saturation mechanisms were adequate to explain the observed parameter changes. These changes also accounted for the observed mean plasma zinc mass increase of only 37% above pre-load levels in face of an 11-fold increase in zinc intake.

Deficient production of 1,25-dihydroxyvitamin D in elderly osteoporotic patients

There is uncertainty about the adequacy of renal secretion of 1,25-dihydroxyvitamin D(1,25-(OH)2-D) in elderly patients with osteoporosis. To investigate this uncertainty, we stimulated secretion of 1,25-(OH)2-D with a 24-hour intravenous infusion of synthetic human parathyroid hormone fragment 1-34 and compared the results in normal young adults and elderly patients with untreated osteoporosis. Serum levels of 1,25-(OH)2-D were similar in both groups (49 +/- 10 and 42 +/- 9 pg per milliliter [116 +/- 24 and 99 +/- 21 pmol per liter]) before the infusion. However, during the 24-hour infusion, serum levels nearly doubled (P less than 0.01) in the normal volunteers but did not change significantly in the patients. Serum ionized calcium increased and serum inorganic phosphate decreased similarly in both groups during the infusion (P less than 0.05). Although the present study does not establish whether deficient 1,25-(OH)2-D secretory reserve is an effect of age or of osteoporosis, it is possible that such a deficiency will explain the inability of elderly osteoporotic patients to adapt to the low-calcium diets common in this age group. If so, this phenomenon may play a part in the pathogenesis of age-related osteoporosis.

Progressing alteration of parathyroid function in cattle from experimental high and low calcium feeding

Changes in function of the parathyroid gland was studied periodically for 36 days in two groups of calves fed high and low calcium diets. After changes to the experimental diets, parathyroid function was altered in some calves at 9 days of high or low calcium feeding. Parathyroid function was reduced in high calcium feeding and increased in low calcium feeding. These changes increased progressively in intensity with the lapse of time during experimental feeding periods.

Lighting for the elderly: a psychobiological approach to lighting

The present paper reviews the role of illumination in shaping the indoor environment of the elderly person. The approach is that lighting has a twofold impact on the individual. One is as a source of information about the environment, i.e., visual, and the other is photobiological through the skin or photoreceptor.

The visually lighted environment is reviewed, discussing first the physiological changes that occur during the aging process, then the effect of aging on visual performance, and finally the importance of qualitative factors in assessing the adequacy of an illuminated environment for the elderly. Special attention is given to application problems in lighting for the elderly, i.e., excessive brightness differences, discomfort glare, veiling reflections, and the importance of color and the spectral power distribution of the light source. The advantages of a full-spectrum light source which simulates natural sunlight for indoor illumination is discussed in light of recent research.

The biologically lighted environment is reviewed in terms of the potential role that indoor illumination can play in regulating important biochemical processes in the elderly population, i.e., neuroendocrine control, vitamin D3synthesis, immunologic mechanisms, and cardiovascular regulation.

The turnover time of calcium in the exchangeable pools of bone in man and the long-term effect of a parathyroid hormone fragment

(1) A non-compartmental method is described for analysing the kinetics of the exchange of calcium between the bloodstream and the exchangeable bone pools. (2) This method has been applied to studies on osteoporotic patients treated with low doses of an active fragment of human parathyroid hormone. The data of Phang et al. (1969), who studied the effects of dietary calcium peturbation on normal volunteers, were also analysed. (3) It was found that in response to chronic PTH treatment the transit time of calcium in the exchangeable pools decreased. This could not be explained by the observed changes in the calcium accretion rate to the fixed bone pools, and it was necessary to postulate an alteration in the ratio of the rate constants governing the interchange of calcium between bloodstream and exchangeable pools. (4) The changes in the behaviour of the exchangeable pools in response to dietary perturbation could not be explained by the postulated increase in endogenous PTH secretion rate in response to dietary calcium restriction.

Role of parathyroid hormone in regulation of main calcium fluxes in rats

The effect of calcium deprivation on the various calcium fluxes was studied in growing rats either sham-operated (SHAM), thyroparathyroidectomized (TPTX), or thyroparathyroidectomized and supplemented with parathyroid hormone (PTH) (TPTX + PTH). In SHAM rats a decrease in the net absorption of calcium (Vna) has no influence on calcemia or on bone formation (Vo+), but leads to an increase in bone resorption (Vo-). In TPTX rats a decrease in Vna induces a decrease in calcemia and in Vo+ but still causes an increase in Vo-. The same is true in TPTX + PTH rats although all the variables measured are increased. In TPTX rats, both without and with PTH, a linear correlation exists between calcemia and Vo+ suggesting that calcemia influences bone formation. Furthermore, it appears that PTH is important in regulating bone turnover, but that the adaptation of Vo- to a change in Vna can occur in the absence or in the presence of a constant amount of this hormone. The mechanism of regulating this adaptation of bone resorption is still unknown.

The actions of parathyroid hormone on bone: relation to bone remodeling and turnover, calcium homeostasis, and metabolic bone disease. Part IV of IV parts: The state of the bones in uremic hyperaparathyroidism--the mechanisms of skeletal resistance to PTH in renal failure and pseudohypoparathyroidism and the role of PTH in osteoporosis, osteopetrosis, and osteofluorosis

In early chronic renal failure, the state of the bones resembles that of type II primary hyperparathyroidism. Cortical bone becomes thinner and more porous, and there is increased extent of surface remodeling. These changes are followed in turn by osteomalacia and osteitis fibrosa, although sometimes these may be alternate rather than successive stages. Bone turnover is less than would be expected for the elevation of PTH level, probably because of 1,25 (OH)2D3 deficiency. The resorption velocity and lamellar bone appositional rates are depressed, but woven bone appositional rate may be increased, possibly because of hyperphosphatemia. Bone mass reflects the summation of three independent processes: loss of lamellar bone due to hyperparathyroidism (depending on the extent of insulation by osteoid); accumulation of partly mineralized osteoid because of osteomalacia; accumulation of woven bone because of osteitis fibrosa. Osteosclerosis may be growth-related metaphyseal, subchondral or diffuse axial, and periosteal neostosis may also occur. Some patients on hemodialysis lose bone because of planing rather than lacunar or dissecting resorption, combined with depression of both lamellar and woven bone formation. Hyperparathyroid bone disease tends to improve slowly after renal transplantation. Persistent hypocalcemia reflects a defect in the calcium homeostatic system and cannot be explained solely by the known stimuli to secondary hyperparathyroidism. The increment in plasma calcium in response to PTH infusion is subnormal, both in early chronic and in acute renal failure, probably because of 1,25(OH)2D3 deficiency. This is also the most likely explanation for the depressed level of blood-bone equilibrium. The activity of all three of the PTH responsive cell systems in bone is depressed in renal failure, probably because all three require 1,25(OH)2D3 in order to function normally. In pseudohypoparathyroidism, as in chronic renal failure, hypocalcemia results from a defect in the regulation of the blood-bone equilibrium. The bone-remodeling system shows all gradations of response, from slight depression of bone turnover to overt osteitis fibrosa, but bone turnover is never as low as in PTH deficiency. These differences may reflect the presence or absence of resistance to PTH of the osteoprogenitor cell as well as of the calcium homeostatic system, or may be due to varying degrees of 1,25(OH)2D3 deficiency, as in chronic renal failure. An increase in plasma calcium in response to PTH can occur either in the untreated state or after treatment with vitamin D because either the error-correcting or remodeling system remains responsive to PTH. Pseudohypoparathyroidism may be subdivided into three types, depending on whether the urinary cyclic-AMP response to PTH remains defective despite treatment with vitamin D, improves with treatment, or is normal before treatment. Only the former is associated with the genetic syndrome of Albright's hereditary osteodystrophy...

A new method for calculating the accretion rate of bone calcium and some observations on the suitability of strontium-85 as a tracer for bone calcium

1. A new method for calculating the accretion rate (A) of bone calcium is proposed, based on an impulse analysis of 47Ca data. The method is free of most of the assumptions inherent in previous methods of analysis and appears to give more accurate estimates. 2. In fourteen normal subjects and twelve patients with metabolic bone disease, measurements of A by the new method gave very similar results to the mineralization rate calculated by the method of Burkinshaw et al. (1969). Analysis of twelve studies performed by Neer et al. (1967) gave good agreement with their five compartment model. A close relation between A and Marshall's (1964) A5 was observed, but the latter gave systematically higher results. 3. In sixteen studies both 47Ca and 85Sr were injected simultaneously. Although there were no systematic differences between the values of A for the two tracers, the differences between individual values were greater than the known experimental errors.

The effect of diurnal variation on total plasma calcium concentration in normal subjects

In 12 normal subjects plasma calcium and phosphorus concentrations were estimated during a normal working day. In the individual subjects fluctuations from the fasting values occurred during the period of study, but at no time during that period did the mean values differ significantly from the fasting plasma calcium or phosphorus concentrations. In three of the subjects the study was repeated while fasting during a normal working day. In these subjects the fluctuations in both plasma calcium and phosphorus concentrations were less than during a normal day while taking meals, and there was evidence of a diurnal variation in the plasma phosphorus concentration.