Evidence of a probable role for 25-hydroxyvitamin D in the regulation of human calcium metabolism

Influence of Various Factors on Circulating 25(OH) Vitamin D Concentrations in Dogs with Cancer and Healthy Dogs

Background

Low blood 25‐hydroxyvitamin D (25(OH)D) concentrations have been associated with cancer in dogs. Little research has examined what other factors may affect 25(OH)D concentrations.

Objectives

(1) To determine whether the presence of cancer (lymphoma, osteosarcoma, or mast cell tumor [MCT]) in dogs is associated with plasma 25(OH)D concentrations and (2) identify other factors related to plasma 25(OH)D concentrations in dogs.

Animals

Dogs newly diagnosed with osteosarcoma (n = 21), lymphoma (n = 27), and MCT (n = 21) presented to a tertiary referral oncology center, and healthy, client‐owned dogs (n = 23).

Methods

An observational study design was used. Dietary vitamin D intake, sex, age, body condition score (BCS), muscle condition score (MCS), and plasma concentrations of 25(OH)D, 24,25‐dihydroxyvitamin D (24,25(OH)₂D) (a marker of CYP24A1 activity), as well as ionized calcium (ICa), parathyroid hormone, and parathyroid hormone‐related protein concentrations were measured. An analysis of covariance was used to model plasma 25(OH)D concentrations.

Results

Cancer type (P = 0.004), plasma 24,25(OH)₂D concentrations (P < 0.001), and plasma ICa concentrations (P = 0.047) had significant effects on plasma 25(OH)D concentrations. Effects of age, sex, body weight, BCS, MCS, and plasma PTH concentrations were not identified. A significant interaction between ICa and cancer was found (P = 0.005). Plasma 25(OH)D concentrations increased as ICa concentrations increased in dogs with cancer, whereas plasma 25(OH)D concentrations decreased as ICa concentrations increased in healthy dogs.

Conclusions and Clinical Importance

Results support a relationship between cancer and altered vitamin D metabolism in dogs, mediated by plasma ICa concentrations. The CYP24A1 activity and plasma ICa should be measured in studies examining plasma 25(OH)D concentrations in dogs.

Vitamin D and Anaesthesia

Vitamin D is a vitamin not only associated with calcium-phosphorus metabolism but also affects many organ systems. Because of its effect on the immune system in recent years, it has attracted much attention. Vitamin D deficiency is a clinical condition that can be widely observed in the society. Thus, patients with vitamin D deficiency are often seen in anaesthesia practice. In the absence of vitamin D, prolongation of intensive care unit stay, increase in mortality and morbidity and also association of chronic diseases further increase the importance of vitamin D deficiency. The results obtained from studies have led to the question of whether poor surgical outcome is associated with vitamin D deficiency. We assessed the vitamin D deficiency and its negative consequences for the anaesthesiologist.

[Disorders of calcium metabolism]

The majority of clinical complaints derive from disorders of calcium metabolism and are associated with a wide variety of clinical symptoms caused by numerous diseases with entirely different types of pathophysiology. The prognosis varies from favorable to fatal depending on the pathophysiology of the underlying disorder of calcium metabolism; therefore, the diagnostic work-up aims to quickly identify the underlying disease causing the disturbance in calcium homeostasis. Every clinical situation with a diminished state of calcium absorption is treated with calcium and vitamin D in varying doses whereas every disorder with an increased calcium absorptive or resorptive state is treated with improved diuresis in addition to antiresorptive drugs, such as bisphosphonates. In many situations the management of a disturbed calcium balance requires an interdisciplinary approach in order to treat the underlying disease in parallel with correction of the calcium homeostasis.

Allosteric regulation of the calcium-sensing receptor in obese individuals

We have previously reported that the calcium-sensing receptor (CaSR) plays an important role in modulating lipid metabolism under low calcium conditions. The aim of this study was to identify possible regulators of CaSR and the mechanisms of action of CaSR in obese individuals. Subcutaneous fat samples were obtained from 10 obese and 10 non-obese males undergoing elective abdominal surgery. Visceral fat pads were obtained from 12 obese and 12 non-obese male rats. Serum lipid, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) concentrations, as well as the gene and protein expression of CaSR in the white adipose tissue of obese subjects and rats were determined. Serum total calcium, vitamin D, parathyroid hormone (PTH) and amino acid levels in human subjects were measured. Intracellular calcium and cyclic adenosine monophosphate (cAMP) levels in rat adipocytes were measured by laser scanning confocal microscopy and ELISA, respectively. The results revealed that serum triglyceride (TG), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), TNF-α, IL-6 and PTH levels were significantly higher in the obese individuals versus the controls. By contrast, serum vitamin D and amino acid concentrations were lower in the obese individuals versus the controls. In addition, intracellular calcium levels were higher, while cAMP levels were lower in the obese rat adipocytes compared with the control group. However, the gene and protein expression of CaSR in white adipose tissue did not differ between the obese groups and the controls. Thus, these results suggest that CaSR functions not through its expression, but rather through allosteric regulation in obese individuals.

How vitamin D works on bone

Vitamin D is important for the normal development and maintenance of bone. The elucidation of the vitamin D activation pathway and the cloning of the vitamin D receptor have advanced our understanding of the actions of vitamin D on bone. The preponderance of evidence indicates that 1,25(OH)₂D₃ enhances bone mineralization through its effects to promote calcium and phosphate absorption. Although 1,25(OH)₂D₃ stimulates bone resorption in vitro, treatment in vivo can prevent bone loss and fracture through several potential mechanisms. The development of vitamin D analogues has provided new therapeutic options for increasing bone mineral density and reducing fractures.

Vitamin D substrate-product relationship in idiopathic hypercalciuria

Absorptive hypercalciuria (AH) is associated with elevated levels of 1,25-dihydroxyvitamin D (1,25(OH)(2)D). While no increase of 1,25(OH)(2)D after oral administration of 25-hydroxyvitamin D (25OHD) at high doses has been claimed in normal subjects, a substrate-product relationship has been reported in normal children, young people after UV irradiation, older persons, postmenopausal women, primary hyperparathyroidism, renal failure, osteomalacia, and sarcoidosis. No data of this relationship in AH is available. To investigate 25OHD-1,25(OH)(2)D substrate-product relationship in AH, 161 AH patients (mean age 60.9+/-11.7 years) and 110 age- and sex-matched controls (mean age 61.5+/-12.4 years) were studied. In 57 controls and 52 AH subjects 25OHD-1,25(OH)(2)D relationship in basal conditions and after 2-week oral 25OHD (25 microg/day) administration were evaluated. In basal conditions 25OHD and 1,25(OH)(2)D were correlated in both, controls and AH; 25OHD treatment was followed by an increase in serum 25OHD and 1,25(OH)(2)D in both groups. However, delta responses of 25OHD and 1,25(OH)(2)D to 25OHD were higher in AH suggesting an enhanced activity of 1 alpha-hydroxylase. In conclusion, the higher response of 1,25(OH)(2)D after oral 25OHD in AH patients suggests a differential capacity between both groups in handling the increases in 1,25(OH)(2)D.

Body size and serum 25 hydroxy vitamin D response to oral supplements in healthy older adults

BACKGROUND

Vitamin D insufficiency is prevalent in the northeast United States. Since vitamin D insufficiency is readily amenable to supplementation, it is important to understand what factors are associated with serum 25 hydroxy vitamin D (25(OH)D) response to vitamin D supplementation.

OBJECTIVE

In this study we examined the association of serum 25(OH)D response to vitamin D supplementation with body size in a population of elderly subjects.

METHODS

257 healthy, ambulatory men and women 65 years of age or older were randomly assigned to treatment with either 700 IU/day (17.5 microg/d) of supplemental vitamin D(3) and 500 mg/day (12.5 mmol/d) of supplemental calcium, or to placebo.

RESULTS

In multivariate regression analyses, after adjusting for baseline 25(OH)D, season, and sex, we found change in 25(OH)D to be inversely associated with baseline BMI (p = 0.01) in subjects treated with supplements for one year. Change in 25(OH)D was also negatively associated with other baseline anthropometric measurements in these subjects.

CONCLUSION

Our study implies that body size should be taken into account when estimating the amount of vitamin D intake needed to raise 25(OH)D to the desired level.

Season of diagnosis is a predictor of cancer survival. Sun-induced vitamin D may be involved: a possible role of sun-induced Vitamin D

The calcidiol level in a group of Norwegians (14,000 individuals, age range 16-80) was found to be highest in late summer. The seasonal variation was larger for young than for old persons. The calcitriol concentration was practically constant throughout the year. Younger persons had less calcidiol and more calcitriol than older persons, indicating that the conversion of calcidiol to calcitriol is more efficient in younger persons. A seasonal variation of prognosis of cancer (colon-, breast-, prostate- cancer and Hodgkin lymphoma) was found. The survival is highest for summer and autumn diagnosis, corresponding to maximal calcidiol levels. Thus, calcidiol may act synergistically with traditional treatment modalities. In view of these calcitriol and calcidiol data, the seasonal variation of cancer survival may be related to the calcidiol gradient, indicating that this Vitamin D metabolite may be more important than believed so far.

Reference range for serum parathyroid hormone

OBJECTIVE

To determine whether the reference range for parathyroid hormone (PTH) should be lowered (from 65 pg/mL to a proposed value of 46 pg/mL) with use of the Allegro radioimmunometric assay.

METHODS

We examined the reference range for PTH, adjusted for serum 25-hydroxyvitamin D (25-OHD), in 503 healthy African American and white women, who were 20 to 80 years old. We also analyzed other factors that are thought to influence PTH levels.

RESULTS

Univariate predictors of PTH were identified, and a multivariate model was developed with use of the variables and PTH. Serum PTH was significantly higher in black study subjects than in white study subjects (P<0.02). Increasing PTH was also significantly correlated with increasing body mass index, age, and serum creatinine and with decreasing dietary calcium intake and serum 25-OHD levels. A stepwise multiple linear regression analysis yielded the following predictors of PTH: body mass index (R2=9.4%), age (R2=1.0%), and serum 25-OHD (R2=0.8%). In our study population, many PTH values were above the proposed new upper limit of 46 pg/mL.

CONCLUSION

The upper limit of the reference range for serum PTH should not be changed. Factors to be considered in analysis of serum PTH values in the upper reference range in patients with normocalcemia include obesity, race, 25-OHD levels, advanced age, serum creatinine, and dietary calcium intake.

Relation between calcium intake and fat oxidation in adult humans

OBJECTIVE

To determine if total calcium (Ca(2+)) intake and intake of Ca(2+) from dairy sources are related to whole-body fat oxidation.

DESIGN

: Cross-sectional study.

SUBJECTS

A total of 35 (21 m, 14 f) non-obese, healthy adults (mean+/-s.d., age: 31+/-6 y; weight: 71.2+/-12.3 kg; BMI: 23.7+/-2.9 kg m(-2); body fat: 21.4+/-5.4%).

MEASUREMENTS

Daily (24 h) energy expenditure (EE) and macronutrient oxidation using whole-room indirect calorimetry; habitual Ca(2+) intake estimated from analysis of 4-day food records; acute Ca(2+) intake estimated from measured food intake during a 24-h stay in a room calorimeter.

RESULTS

Acute Ca(2+) intake (mg. kcal(-1)) was positively correlated with fat oxidation over 24 h (r=0.38, P=0.03), during sleep (r=0.36, P=0.04), and during light physical activity (r=0.32, P=0.07). Acute Ca(2+) intake was inversely correlated with 24-h respiratory quotient (RQ) (r=-0.36, P=0.04) and RQ during sleep (r=-0.31, P=0.07). After adjustment for fat mass, fat-free mass, energy balance, acute fat intake, and habitual fat intake, acute Ca(2+) intake explained approximately 10% of the variance in 24-h fat oxidation. Habitual Ca(2+) intake was not significantly correlated to fat oxidation or RQ. Total Ca(2+) intake and Ca(2+) intake from dairy sources were similarly correlated with fat oxidation. In backwards stepwise models, total Ca(2+) intake was a stronger predictor of 24 h fat oxidation than dairy Ca(2+) intake.

CONCLUSION

Higher acute Ca(2+) intake is associated with higher rates of whole-body fat oxidation. These effects were apparent over 24 h, during sleep and, to a lesser extent, during light physical activity. Calcium intake from dairy sources was not a more important predictor of fat oxidation than total Ca(2+) intake.

1alpha,25-Dihydroxyvitamin D3 modulates human adipocyte metabolism via nongenomic action

We reported recently that suppression of the renal 1alpha,25-dihyroxyvitamin D3 (1lpha,25-(OH)2-D3) production in aP2-agouti transgenic mice by increasing dietary calcium decreases adipocyte intracellular Ca2+ ([Ca2+]i), stimulates lipolysis, inhibits lipogenesis, and reduces adiposity. However, it was not clear whether this modulation of adipocyte metabolism by dietary calcium is a direct effect of inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i. Accordingly, we have now evaluated the direct role of 1alpha,25-(OH)2-D3. Human adipocytes exhibited a 1alpha,25-(OH)2-D3 dose-responsive (1-50 nM) increase in [Ca2+]i (P<0.01). This action was mimicked by 1alpha,25-dihyroxylumisterol3 (1alpha,25-(OH)2-lumisterol3) (P<0.001), a specific agonist for a putative membrane vitamin D receptor (mVDR), and completely prevented by 1b,25-dihydroxyvitamin D3 (1beta,25-(OH)2-D3), a specific antagonist for the mVDR. Similarly, 1alpha,25-(OH)2-D3 (5 nM) caused 50%-100% increases in adipocyte fatty acid synthase (FAS) expression and activity (P<0.02), a 61% increase in glycerol-3-phosphate dehydrogenase (GPDH) activity (P<0.01), and an 80% inhibition of isoproterenol-stimulated lipolysis (P<0.001), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. Notably, 1alpha,25-(OH)2-lumisterol3 exerted more potent effects in modulating adipocyte lipid metabolism, with 2.5- to 3.0-fold increases in FAS expression and activity (P<0.001) and a threefold increase in GPDH activity (P<0.001). Also 1alpha,25-(OH)2-lumisterol3 was approximately twice as potent in inhibiting basal lipolysis (P<0.025), whereas 1beta,25-(OH)2-D3 completely blocked all these effects. These data suggest that 1alpha,25-(OH)2-D3 modulates adipocyte Ca2+ signaling and, consequently, exerts a coordinated control over lipogenesis and lipolysis. Thus, a direct inhibition of 1alpha,25-(OH)2-D3-induced [Ca2+]i may contribute to an anti-obesity effect of dietary calcium, and the mVDR may represent an important target for obesity.

Effects of dietary calcium on adipocyte lipid metabolism and body weight regulation in energy-restricted aP2-agouti transgenic mice

We have demonstrated previously a regulatory role for intracellular Ca2+ ([Ca2+]i) in adipocyte lipogenesis and lipolysis and have recently reported that 1,25-(OH)2-D increases adipocyte [Ca2+]i, which causes increased lipogenesis and decreased lipolysis. We have now tested the hypothesis that suppressing 1,25-(OH)2-D by increasing dietary calcium will suppress adipocyte [Ca2+]i, thereby facilitating weight loss by stimulating lipolysis and inhibiting lipogenesis in calorically (Kcal)-restricted (70% of ad lib) aP2-agouti transgenic (aP2-a) mice. Mice (aP2-a) exhibiting a pattern of obesity gene expression similar to humans were fed a low-Ca (0.4%)/high-fat/high-sucrose diet for six weeks, resulting in a 27% and twofold increase in body weight and total fat pad mass, respectively, with a twofold increase in adipocyte [Ca2+]i pad lib or Kcal-restricted (70% of ad lib) on this diet either unsupplemented (basal) or with 25% or 50% of the protein replaced by non-fat dry milk (medium or high) dairy or supplemented with CaCO3 to 1.2% Ca for six weeks. Adipocyte [Ca2+]i was unaffected by Kcal restriction but was reduced markedly by all three high Ca diets (290 vs. 130 nM, p2+]i and thereby reduce energy storage and increase thermogenesis during Kcal restriction.

ApaI polymorphisms of the vitamin D receptor predict bone density of the lumbar spine and not racial difference in bone density in young men

A number of previous investigations showed significant associations between polymorphisms of the vitamin D receptor (VDR) gene and bone mineral density (BMD). BMD is influenced by hormones and the rate of skeletal remodeling. A study was performed to investigate the possible relationship between Apa I, Bsm I, Taq I, and Fok I polymorphisms of the VDR gene and serum 1,25-dihydroxyvitamin D (1,25[OH]2D), osteocalcin, and propeptide of type I collagen (PICP)-markers of bone turnover, total body calcium, and BMD of the total body, radius, lumbar spine, trochanter, and femoral neck-in 39 young adult black men of 20 to 40 years of age and 44 age-, height-, and weight-matched white men. The distribution of each of the four alleles of the VDR genotypes was similar in the two racial groups. The Apa I VDR genotype was associated with serum PICP (P =.0494) but not with serum 1,25(OH)2D or serum osteocalcin. A significant association between the Apa I VDR genotype and BMD of the lumbar spine (P =.0291) was also observed. However, the Bsm I, Taq I, and Fok I genotypes were not significantly associated with BMD or serum osteocalcin, PICP, or 1,25(OH)2D. Multivariate stepwise analysis indicated that (1) the Apa I VDR genotype was associated with BMD of the lumbar spine in the two groups together; with total body calcium and BMD of the total body, radius, trochanter, and femoral neck in the black men; and with BMD of the radius in the white men; analysis also indicated that (2) race was significantly associated with total body calcium and BMD of the total body, lumbar spine, and femoral neck. In summary, the Apa I VDR genotype is associated with serum PICP and BMD at a number of sites but does not contribute to or account for racial differences in BMD in young adult men.

Characterization of 25-hydroxyvitamin D binding protein from intestinal cells

We have previously purified a cytosolic vitamin D metabolite binding protein (cDBP) from rat enterocytes, which has characteristics distinct from other vitamin D binding proteins. In these studies, we demonstrate that cDBP in a semi-purified fraction from human intestinal cells (Caco-2 cells) binds 25-hydroxyvitamin D (25OHD) with at least a 1000-fold greater affinity than 1, 25-dihydroxyvitamin D (1,25(OH)(2)D) or 24,25-dihydroxyvitamin D. Treatment of cells with 1,25(OH)(2)D reduced 25OHD binding to approximately one third that of the untreated cells (0.42 CPM/mg total protein vs 1.34 CPM/mg total protein, respectively). Finally, the cDBP is not immunoreactive to antibodies prepared against the C-terminus of the nuclear vitamin D receptor (VDR). In summary, cDBP bound 25OHD with greater affinity than either 1,25(OH)(2)D or 24,25 dihydroxyvitamin D, the cytosolic binding activity was down-regulated by 1,25(OH)(2)D and cBDP is distinct from the nuclear VDR.

Decreased bioavailability of vitamin D in obesity

BACKGROUND

Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism.

OBJECTIVE

This study assessed whether obesity alters the cutaneous production of vitamin D(3) (cholecalciferol) or the intestinal absorption of vitamin D(2) (ergocalciferol).

DESIGN

Healthy, white, obese [body mass index (BMI; in kg/m(2)) > or = 30] and matched lean control subjects (BMI </= 25) received either whole-body ultraviolet radiation or a pharmacologic dose of vitamin D(2) orally.

RESULTS

Obese subjects had significantly lower basal 25-hydroxyvitamin D concentrations and higher parathyroid hormone concentrations than did age-matched control subjects. Evaluation of blood vitamin D(3) concentrations 24 h after whole-body irradiation showed that the incremental increase in vitamin D(3) was 57% lower in obese than in nonobese subjects. The content of the vitamin D(3) precursor 7-dehydrocholesterol in the skin of obese and nonobese subjects did not differ significantly between groups nor did its conversion to previtamin D(3) after irradiation in vitro. The obese and nonobese subjects received an oral dose of 50000 IU (1.25 mg) vitamin D(2). BMI was inversely correlated with serum vitamin D(3) concentrations after irradiation (r = -0.55, P: = 0.003) and with peak serum vitamin D(2) concentrations after vitamin D(2) intake (r = -0.56, P: = 0.007).

CONCLUSIONS

Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments.

Improved cholecalciferol nutrition in rats is noncalcemic, suppresses parathyroid hormone and increases responsiveness to 1, 25-dihydroxycholecalciferol

We examined how cholecalciferol (vitamin D) nutrition affected serum 25-hydroxycholecalciferol (25(OH)D) and 1, 25-dihydroxycholecalciferol (1,25(OH)(2)D). Rats were fed conventional diet (vitamin D, 4.5 IU/g, or 7 nmol/d) or the same diet plus 18 nmol/d of extra vitamin D for 3 wk. The extra vitamin D resulted in greater serum 25(OH)D (51 +/- 3, vs. control of 21 +/- 2 nmol/L), and kidney mRNA for vitamin D receptor [VDR mRNA] (P = 0. 026) and lower serum 1,25(OH)(2)D (72 +/- 16 vs. control of 161 +/- 10 pmol/L, P = 0.001), and parathyroid hormone (PTH) (89 +/- 4 vs. control of 160 +/- 15 ng/L, P = 0.001). Kidney VDR mRNA relative to GAPDH mRNA correlated inversely with serum 1,25(OH)(2)D (r = -0.714, P = 0.006). There were no differences in serum calcium, phosphate, alkaline phosphatase, or weight gain. Experiment 2 compared groups supplemented with 0.2, 2 or 20 nmol/d of vitamin D orally, or 20 nmol/d dermally to see how vitamin D nutrition influenced the response of 1,25(OH)(2)D to changes in diet calcium. Vitamin D did not affect urinary calcium or pyridinoline excretion, serum calcium, phosphate, vitamin D binding protein or alkaline phosphatase. In groups given 20 nmol/d of vitamin D, renal mitochondrial 25(OH)D-1alpha-hydroxylase was lower (P < 0.01) and 25(OH)D-24-hydroxylase was higher (P < 0.05). Higher 25(OH)D concentration was related to proportionally lower 1,25(OH)(2)D at every calcium intake, indicating greater tissue sensitivity to 1, 25(OH)(2)D. We conclude suppression of 1,25(OH)(2)D and PTH, and higher renal VDR mRNA and 24-hydroxylase did not involve higher free 1,25(OH)(2)D concentration or a first pass effect at the gut. Thus, 25(OH)D or a metabolite other than 1,25(OH)(2)D is a physiological, transcriptionally and biochemically active, noncalcemic vitamin D metabolite.

Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety

For adults, the 5-microg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension. Total-body sun exposure easily provides the equivalent of 250 microg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit. Sailors in US submarines are deprived of environmentally acquired vitamin D equivalent to 20-50 microg (800-2000 IU)/d. The assembled data from many vitamin D supplementation studies reveal a curve for vitamin D dose versus serum 25-hydroxyvitamin D [25(OH)D] response that is surprisingly flat up to 250 microg (10000 IU) vitamin D/d. To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 microg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 microg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of > or = 1000 microg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 microg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 microg (2000 IU)/d is too low by at least 5-fold.

Postoperative tetany in Graves disease: important role of vitamin D metabolites

OBJECTIVE

To test the authors' hypothesis of the causal mechanism(s) of postoperative tetany in patients with Graves disease.

SUMMARY BACKGROUND DATA

Previous studies by the authors suggested that postoperative tetany in patients with Graves disease occurs during the period of bone restoration and resulted from continuation of a calcium flux into bone concomitant with transient hypoparathyroidism induced by surgery.

PATIENTS AND METHODS

A prospective study was carried out to investigate sequential changes in serum levels of intact parathyroid hormone (iPTH), calcium and other electrolytes, 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D (1,25(OH)2D), and bone metabolic markers in 109 consecutive patients with Graves disease who underwent subtotal thyroidectomy.

RESULTS

Preoperative serum iPTH levels negatively correlated with ionized calcium levels and positively correlated with 1,25(OH)2D or 1,25(OH)2D/25OHD. After the operation, there was a significant decline in levels of ionized calcium, magnesium, and iPTH. Serum iPTH was not detected in 15 patients after surgery. Four of these 15 patients, and 1 patient whose iPTH level was below normal, developed tetany. Preoperative serum ionized calcium levels were significantly lower, and iPTH levels were higher, in the 5 patients with tetany than in the 11 patients who did not develop tetany despite undetectable iPTH levels. The tetany group had significantly lower serum 25OHD levels and higher 1,25(OH)2D levels, and had increased 1,25(OH)2D/25OHD as an index of the renal 25OHD-1-hydroxylase activity than those in the nontetany group. These results suggest that patients with a high serum level of iPTH as a result of low serum calcium levels (secondary hyperparathyroidism) are susceptible to tetany under conditions of hypoparathyroid function after surgery.

CONCLUSIONS

Postoperative tetany occurs in patients with secondary hyperparathyroidism caused by a relative deficiency in calcium and vitamin D because of their increased demand for bone restoration after preoperative medical therapy concomitant with transient hypoparathyroidism after surgery. Calcium and vitamin D supplements may be recommended before and/or after surgery for patients in whom postoperative tetany is expected to develop.

Calcium absorptive effects of vitamin D and its major metabolites

The absorptive response to graded doses of vitamin D3, 25(OH)D, and 1,25(OH)2D was measured in healthy adult men after treatment periods of eight, four, and two weeks, respectively. While no relationship was found between baseline absorption and serum vitamin D metabolite levels, all three vitamin D compounds significantly elevated 45Ca absorption from a 300 mg calcium load given as part of a standard test meal. 1,25(OH)2D was active even at the lowest dose (0.5 microgram/day), and the slope was such that doubling of absorption would occur at an oral dose of approximately 3 micrograms/day. 25(OH)D was also active in elevating absorption and did so without raising total 1,25(OH)2D levels. On the basis of the dose response curves for 1,25(OH)2D and 25(OH)D, the two compounds exhibited a molar ratio for physiological potency of approximately 100:1. The absorptive effect of vitamin D3 was seen only at the highest dose level (1250 micrograms, or 50,000 IU/day) and was apparently mediated by conversion to 25(OH)D. Analysis of the pooled 25(OH)D data from both the 25(OH)D- and vitamin D3-treated groups suggests that approximately one eighth of circulating vitamin D-like absorptive activity under untreated conditions in winter may reside in 25(OH)D. This is a substantially larger share than has been predicted from studies of in vitro receptor binding.

The cause of maintained hypercalciuria after the surgical cure of primary hyperparathyroidism is a defect in renal calcium reabsorption

The hypercalciuria that eventually remains after the successful removal of a solitary parathyroid adenoma may originate from excessive intestinal calcium absorption, bone resorption or deficient renal reabsorption. In order to clarify this question, ten patients surgically cured from primary hyperparathyroidism (PHPx), ten age-matched normal subjects and five nephrolithiasic patients with renal hypercalciuria (RH) were studied after five days on a low calcium diet, either during fasting or after oral calcium load. Fasting serum calcium, amino-terminal and intact PTH levels and also urinary cAMP excretion were normal in every individual patient. Serum ionized calcium and inulin clearance (GFR) were used for calculations of the filtered load (FL Ca) and the fractional excretion of calcium (FE Ca). Six PHPx patients displayed fasting calciuria above the upper limit calculated for control subjects, despite having the lowest GFR and FL Ca (p < 0.05 vs control). These patients (h-PHPx) had a small calciuric response to oral calcium load. Serum 1,25-(OH)2D3 and 25OHD3 did not correlate with calciuria. Our findings exclude intestinal hyperabsorption and excessive bone resorption in h-PHPx patients, and strongly suggest a renal tubular defect in calcium reabsorption as the cause of their hypercalciuria. This defect could be primary, as in RH, but only three hPHPx patients had recurrent kidney stones before surgery. On the other hand, as a negative correlation between GFR and FE Ca was only found in PHPx patients, it seems probable that the disturbances in glomerular and tubular functions were secondary to the long standing hypercalcemic hyperparathyroidism.

25-Hydroxyvitamin D3 reverses alteration of the vitamin D-endocrine system in blacks

BACKGROUND

Previous findings indicated that serum 25-hydroxyvitamin D and urinary calcium are decreased and serum immunoreactive parathyroid hormone, serum 1,25-dihydroxyvitamin D, and urinary cyclic adenosine 3',5'-monophosphate are increased in normal black compared to normal white subjects. Studies were carried out to determine if alteration of the vitamin D-endocrine system in blacks is reversed by oral supplementation with 25-hydroxyvitamin D3.

PATIENTS AND METHODS

Eight normal young adult black men and women were admitted two times to a metabolic ward for 2.5 days and studied after no treatment and again after treatment for 1 week with oral 25-hydroxyvitamin D3, 40 to 60 micrograms/d. Six of the subjects underwent a postcontrol study after discontinuation of treatment.

RESULTS

25-Hydroxyvitamin D3 treatment significantly increased serum 25-hydroxyvitamin D and urinary calcium and reduced serum 1,25-dihydroxyvitamin D and urinary cyclic adenosine 3',5'-monophosphate, an index of function of parathyroid hormone. In a postcontrol study, values for serum 25-hydroxyvitamin D, serum 1,25-dihydroxyvitamin D, and urinary calcium had returned to control values.

CONCLUSIONS

The results provide evidence that reduction of serum 25-hydroxyvitamin D contributes to or accounts for alteration of the vitamin D-endocrine system in black subjects.

Comparison of the suppressive effect of two doses (500 mg vs 1500 mg) of oral calcium on parathyroid hormone secretion and on urinary cyclic AMP

The respective effects of the ingestion of two different doses of calcium (500 and 1500 mg) on serum ionized calcium, intact parathyroid hormone (PTH 1-84), and the urinary excretion of 3',5'-cyclic adenosine monophosphate (cyclic AMP) were evaluated in 15 young male adults. Ionized serum calcium and PTH 1-84 were measured before and 1 hour, 2 hours and 3 hours (P1, P2, and P3) after the oral intake of calcium. Cyclic AMP was measured in 2-hour urine samples collected before and during 4 hours after the ingestion of calcium. Similar increments in serum ionized calcium (delta Ca2+) were observed except at P3 where the delta Ca2+ was significantly (P < 0.02) higher after 1500 mg (0.088 mmol/liter) than after 500 mg of (0.062 mmol/liter). In the same way, the comparison of the PTH 1-84 concentrations showed no statistical difference except at P3 (P < 0.002). When expressed as a percentage of P0, the P1 and P2 PTH 1-84 values were more suppressed after 1500 mg than after 500 mg of calcium (P1: -69% vs -59%; P < 0.02; P2: -66% vs -50%; P < 0.02). However, the simultaneous cyclic AMP responses (-24% vs -19%) were not significantly different. The results show that the respective maximal effects on PTH secretion and on urinary cyclic AMP of two very different oral doses of calcium are only slightly different.

Demonstration of a difference in urinary calcium, not calcium absorption, in black and white adolescents

Bone mineral density (BMD) of the forearm, lumbar spine, and femoral neck is greater in black than in white children. Studies were performed to determine whether differences in intestinal absorption of calcium or urinary calcium or both account for an assumed more positive calcium balance and greater bone mass in black children. Normal black and white boys and girls were admitted to a metabolic ward and given a constant daily diet containing 1000 mg calcium, 60% as calcium carbonate, for 2 1/2 days (study I) or 3 1/2 days (study II). Fasting blood and 24 h urine collections were obtained, and in study II, unidirectional fractional absorption of calcium (alpha) was determined with stable isotopes of calcium. It was found that (1) serum 25-hydroxyvitamin D (25-OHD) and urinary calcium were lower and serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] was higher in black than in white children, and (2) alpha was higher in boys than in girls with no racial difference, and (3) there were significant positive correlations between alpha and urinary calcium in the blacks and in the black and white children together. It is concluded that (1) alpha is higher in boys than in girls and (2) a lower urinary calcium, not increased intestinal absorption of calcium, is the means for a more positive calcium balance in blacks that accounts for the racial difference in BMD.

Osteoporosis and increased bone fractures in cerebrotendinous xanthomatosis

Significant osteoporosis determined by skeleton radiography and bone densitometry was found in 15 patients with cerebrotendinous xanthomatosis (CTX) whose mean age was 31 +/- 11 years. In three CTX patients, bone biopsies confirmed osteoporosis. Nine patients also sustained bone fractures following minimal trauma. Serum 25-hydroxyvitamin D ([25-OHD] 14.6 +/- 6.6 ng/mL v [normal] 30.4 +/- 8.0 ng/mL; P < .001) and 24,25-dihydroxyvitamin D ([24,25(OH)2D] 1.2 +/- 0.4 ng/mL v [normal] 2.7 +/- 0.8 ng/mL; P < .001) levels were low. Serum concentrations of 1,25(OH)2D, calcium, inorganic phosphorus, alkaline phosphatase, parathyroid hormone, and calcitonin were normal. Patients showed classic manifestations of CTX, including dementia, pyramidal and cerebellar insufficiency, peripheral neuropathy, cataracts, and tendon xanthomas associated with elevated serum cholestanol concentrations. These results demonstrate that extensive osteoporosis and increased risk of bone fractures are components of this inherited disease.

Menopausal bone loss is partially regulated by dietary intake of vitamin D

Five years ago we reported results from a cross-sectional study of the effect of nutritional factors on calcium-regulating hormones and bone loss in perimenopausal women. We found an inverse correlation between serum 25-hydroxyvitamin D (25OHD) and immunoreactive parathyroid hormone (PTH), and we postulated that over time, women with lower 25OHD would lose more bone because of increased bone remodeling induced by secondary hyperparathyroidism. We have followed 38 of these women for 5 years. Twenty-two have gone through menopause and we are reporting observations on these 22 subjects. Bone mineral analysis was performed twice a year at the distal and mid-radius using single-photon absorptiometry. The slope of the bone mineral content curve was calculated by least squares. Bone loss increased within 6 months of the rise in serum follicle stimulating hormone (FSH) to greater than 40 mIU/ml. We continued to see a negative correlation between 25OHD and PTH (r = -0.450, P = 0.03). Premenopause, PTH was negatively correlated with the proximal bone mineral content (PBMC) slope (-0.604, P = 0.002). The distal bone mineral content (DBMC) 5-year slope was correlated with dietary vitamin D (r = 0.509, P = 0.02), the higher the intake, the less negative the slope. The 5-year PBMC slope was negatively correlated with serum osteocalcin (OC) levels (r = -0.382, P = 0.08). Before menopause, the change in PBMC was positively correlated with OC (r = 0.450, P = 0.03). Postmenopause, the correlation with DBMC slope was negative (r = -0.506, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in vitamin D status between countries in young adults and the elderly

PURPOSE

To compare vitamin D status between countries in young adults and in the elderly.

MATERIALS AND METHODS

Reports on vitamin D status (as assessed by serum 25-hydroxyvitamin D) from 1971 to 1990 were reviewed. Studies were grouped according to geographic regions: North America (including Canada and the United States); Scandinavia (including Denmark, Finland, Norway, and Sweden); and Central and Western Europe (including Belgium, France, Germany, Ireland, The Netherlands, Switzerland, and the United Kingdom).

RESULTS

Vitamin D status varies with the season in young adults and in the elderly, and is lower during the winter in Europe than in both North America and Scandinavia. Oral vitamin D intake is lower in Europe than in both North America and Scandinavia. Hypovitaminosis D and related abnormalities in bone chemistry are most common in elderly residents in Europe but are reported in all elderly populations.

CONCLUSIONS

The vitamin D status in young adults and the elderly varies widely with the country of residence. Adequate exposure to summer sunlight is the essential means to ample supply, but oral intake augmented by both fortification and supplementation is necessary to maintain baseline stores. All countries should adopt a fortification policy. It seems likely that the elderly would benefit additionally from a daily supplement of 10 micrograms of vitamin D.

Mineral homeostasis in obesity: effects of euglycemic hyperinsulinemia

We explored the effects of insulin on mineral homeostasis in five lean and six moderately obese nondiabetic premenopausal women. Serum and urine minerals were measured before and during the steady-state phase of a euglycemic insulin clamp. Each subject participated in two insulin clamp studies on separate days at insulin infusion rates of 10 and 40 mU/m2/min. Euglycemic hyperinsulinemia was associated with (1) a significant increase in urinary calcium excretion when expressed per minute with no change in total serum calcium; (2) a decrease in urine and serum phosphate; (3) a decrease in serum potassium with no change in urine potassium; and (4) no measurable effects on urine or serum sodium. At any given insulin level, the obese individuals excreted significantly more calcium, phosphate, and potassium per minute than lean controls. While insulin administration had no effect on serum parathyroid hormone (PTH) or vitamin D levels, baseline serum 1,25(OH)2D concentration was significantly higher and serum ultrafilterable calcium was significantly lower in obese subjects than in lean controls.

1,25-Dihydroxyvitamin D-related hypercalcemia in lymphoma: two case reports

We report two patients with non-Hodgkin's lymphoma in whom hypercalcemia and elevated 1,25 dihydroxyvitamin D (1,25-(OH)2D3) levels developed in the absence of any lytic bone lesions. Hypercalcemia responded only transiently to glucocorticoids which were ill tolerated. Intravenous APD administration was needed to circumvene hypercalcemia. Humoral hypercalcemia of malignancy is discussed. Our cases confirm that hypercalcemia associated with elevated 1,25-(OH)2D3 may occur in malignant lymphoma.

Dietary calcium and chronic diseases

The Agricultural Revolution was almost certainly associated with a substantial decrease in human calcium intake. Calcium intakes typical of contemporary humans may well be inadequate for many individuals. Various slowly developing chronic disorders such as osteoporosis, hypertension, hyperlipidemia, and colon cancer may be induced or exaggerated by the current low level of dietary calcium intake in Western societies. We propose two hypotheses relating calcium intake to diverse diseases: first, the adaptation required to adjust to low intakes is inadequate to maintain critical components of cellular calcium regulation; second, the constant, forced adaptive response to low intake itself produces untoward consequences.

Alteration of vitamin D metabolism in Mexican-Americans

Studies were performed to investigate vitamin D metabolism in Mexican-Americans. Groups of 15 whites and 16 Mexican-Americans ranging in age from 18 to 41 years were evaluated. All of them were within 25% of their ideal body weight. Each of them was admitted to the Clinical Research Center of the University of Texas Health Science Center and placed on a daily diet estimated to contain 400 mg calcium and 900 mg phosphate. It was found that whereas serum vitamin D (1.8 +/- 0.5 versus 7.6 +/- 1.3 ng/ml, P less than 0.001) and serum 25-hydroxyvitamin D (9 +/- 1 versus 17 +/- 2 ng/ml, P less than 0.01) were significantly lower and serum 1,25-dihydroxyvitamin D (37 +/- 2 versus 28 +/- 2 pg/ml, P less than 0.001) was significantly higher in the Mexican-Americans than in the whites, serum calcium (9.1 +/- 0.1 versus 9.2 +/- 0.1 mg/dl), magnesium (1.84 +/- 0.07 versus 1.80 +/- 0.07 mEq/liter), and Gla protein (19 +/- 3 versus 21 +/- 2 ng/ml) were not different in the two groups. Urinary calcium (144 +/- 14 versus 124 +/- 16 mg/day), phosphate (672 +/- 51 versus 683 +/- 44 mg/day), sodium (110 +/- 8 versus 99 +/- 9 mEq/day), potassium (43 +/- 4 versus 49 +/- 3 mEq/day), and magnesium (7.3 +/- 0.7 versus 7.7 +/- 0.5 mEq/day) and creatinine clearance (173 +/- 14 versus 154 +/- 7 liters/day) were not different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)