Serum concentration of vitamin D metabolites during treatment with vitamin D2 and D3 in normal premenopausal women

Serum concentrations of vitamin D metabolites were measured in 19 healthy premenopausal women before and during treatment with 4000 IU per day of either vitamin D2 or vitamin D3 for 8 weeks. Vitamin D2 treatment increased the serum concentration of 25(OH)D2, but a corresponding decrease in 25(OH)D3 resulted in an unchanged value for total 25(OH)D. The serum concentration of the D3 dihydroxy metabolites was also significantly decreased. Vitamin D3 treatment increased the serum concentrations of 25(OH)D3 and D3 dihydroxy metabolites. The serum concentration of 1,25(OH)2D did not change in either of the treatment groups. We conclude that vitamin D2 and vitamin D3 given in the same doses in international units have a different effect on the serum concentration of vitamin D metabolites and biochemical indices of calcium metabolism.

Serum vitamin D2 and vitamin D3 metabolite concentrations and absorption of vitamin D2 in elderly subjects

The serum vitamin D2 and vitamin D3 metabolite concentrations and intestinal absorption of vitamin D2 were determined in healthy ambulatory and chronically institutionalized elderly subjects with normal renal function. The 25-hydroxyvitamin D (25OHD) concentrations were normal in all subjects (range, 8-43 ng/ml), although institutionalized subjects had a significantly lower mean value [19.2 +/- 2 (+/- SEM) ng/ml; P less than 0.01] compared with ambulatory subjects (25.3 +/- 2 ng/ml). All but one ambulatory subject had 25OHD3 as the major circulating form, whereas 25OHD2 was the major circulating metabolite in one third of the institutionalized subjects. The mean 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentration in both groups was normal, but nine subjects had levels at or below the lower limit of normal despite normal 25OHD concentrations. Separate assay of 1,25-(OH)2D2 and 1,25(OH)2D3 revealed proportional distributions similar to those for 25OHD2 and 25OHD3. To study the effect of age on the intestinal absorption of vitamin D, we compared serum vitamin D2 concentrations after oral administration of 50,000 IU vitamin D2 in both healthy vitamin D-sufficient elderly subjects and young adults. We found no evidence of malabsorption of vitamin D in the elderly subjects. In summary, elderly subjects in New York, whether institutionalized or not, have normal serum 25OHD concentrations. However, while most elderly subjects have normal serum 1,25-(OH)2D levels, a significant proportion fail to produce normal concentrations of 1,25-(OH)2D, possibly due to age-related disturbances in renal synthesis of the hormone.

Assessment of a two-step high-performance liquid chromatographic assay using dual-wavelength ultraviolet monitoring for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol in human serum or plasma

The technique of dual-wavelength monitoring was used to verify the purity of high-performance liquid chromatographic (HPLC) peaks quantified as 25-hydroxyergocalciferol and 25-hydroxycholecalciferol. The data obtained show the need for a second HPLC step prior to quantitation. Potential inaccuracy arising from inadvertent collection of radio-labelled decomposition products was assessed. Between-day coefficients of variation were 7.3, 5.0 and 3.6%, respectively for 11.3 (n = 12), 17.1 (n = 14), and 32.9 (n = 8) ng/ml of 25-hydroxycholecalciferol. For 25-hydroxyergocalciferol, these values were 6.4 and 3.8% for 11.1 (n = 12) and 20.1 (n = 8) ng/ml concentrations, respectively. Comparison of total 25-hydroxycalciferol with a competitive protein binding assay was made. The comparison produced a correlation coefficient (r) of 0.94 and a relationship of y = 1.03x + 3.3. Four of the samples contained more than 10 ng/ml of 25-hydroxyergocalciferol and the results are consistent with the reported 100% cross-reactivity of the competitive binding protein method for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol. A simple regeneration procedure is also described which enables Sep-Pak C18 cartridges to be reused up to eighteen times. Samples may be stored at -18 degrees C for upto several months before assay and either serum or plasma may be used.

Vitamin D supplementation during pregnancy: effect on neonatal calcium homeostasis

We assessed whether modification of vitamin D nutritional status during the last trimester of pregnancy affects maternal and neonatal calcium homeostasis. At the end of the first trimester, 40 pregnant women were randomly assigned to either of two groups, and blood taken to assess the basal values of Ca, Pi, Mg, iPTH, 25-OHD, and 1,25(OH)2D. From the sixth month on, group 1 (+D) received 1000 IU vitamin D3 daily; group 2 (-D) served as control. At the time of delivery, maternal serum 25-OHD was higher in the +D group (P less than 0.0005). Ca, Pi, iPTH, and 1,25(OH)2D were not affected. At term, venous cord 25-OHD levels were also higher in the +D group (P less than 0.0005), and 1,25(OH)2D levels slightly lower (P less than 0.05), but neither Ca, Pi, nor iPTH differed between the two groups. Serum CaT dropped significantly (P less than 0.002) at 4 days of age in the infants from both groups, although to a lesser extent in these from the +D group (P less than 0.05). Circulating iPTH increased in both groups. Serum 25-OHD remained low in the -D group, and dropped slightly in the +D group; 1,25(OH)2D remained stable during the first 4 days of life in the -D group, and increased in the +D group (P less than 0.001). Our data demonstrate the importance of providing adequate maternal vitamin D stores to ensure better perinatal handling of calcium. This is of particular importance for populations at risk for hypovitaminosis D.

Parameters related to 25-OH-D levels in a population-based study of women

We surveyed calcidiol levels (25-OH-D) in a geographically-defined population of 373 women, ages 20-80 yr to test for an association between occult osteomalacia and excess bone loss. Bone mass was measured by photon densitometry and an estimate of vitamin D was determined by measuring dietary and supplemental intake as well as sunlight exposure equivalent. The relationship of smoking practices, alcohol use, exogenous estrogen use, and medications to calcidiol level was assessed. Calcidiol levels were not associated with bone mass levels observed at two different forearm sites. Low levels of calcidiol, indicative of generalized vitamin D deficiency, were not observed in this population though mean estimates of vitamin D intakes from food 119 +/- 148 IU) or food and supplements (319 +/- 463 IU) were less than the Recommended Dietary Allowance (400 IU). Calcidiol was significantly associated with estimates of vitamin D intake from food (r = 0.11), supplement use (r = 0.21), and sunlight equivalent exposure (r = 0.26). Calcidiol levels were negatively related to age (p = 0.0020) and positively related to exogenous estrogen use and premenopausal state independent of age.

Seasonal changes in the biochemical indices of vitamin D deficiency in the elderly: a comparison of people in residential homes, long-stay wards and attending a day hospital

The seasonal changes in the biochemical indices of vitamin D nutrition have been measured in elderly people with differing requirements for institutionalized care. Residents of local authority homes (LAH) showed an increase in serum 25-hydroxyvitamin D3 [25(OH)D3] between spring and autumn (means 14-17 nmol/l, P less than 0.002). No significant seasonal changes were seen in patients on long-stay wards [(GW) serum 25(OH)D3 9.5 and 9.5 nmol/l] and in day-hospital attenders [(GDH) 25 and 26.8 nmol/l]. Significant differences (P less than 0.02 to P less than 0.0001) were found between the mean serum 25(OH)D3 amongst the three groups. A significant linear relationship (r = 0.84, P = 0.036) was found between mean serum 25-hydroxyvitamin D2[25(OH)D2] and dietary vitamin D2. The intake of vitamin D was suboptimal in all groups. The incidence of 25-hydroxyvitamin D deficiency [25(OH)D less than 12.5 nmol/l] varied from 11.7% of residents in LAH in autumn to 47% of GW patients in spring; but hypocalcaemia occurred less often (LAH 1.3% in autumn, GW 4.7% in spring). The diet assumes a greater role in protecting against vitamin D deficiency when the total 25(OH)D is low. Because most diets contain insufficient amounts of vitamin D, elderly institutionalized people will remain at high risk of developing vitamin D deficiency unless specific preventative measures are adopted.

Calcium and vitamin D metabolism in children with nephrotic syndrome

Although abnormalities of calcium and vitamin D metabolism are recognized in children with nephrotic syndrome, longitudinal observations are not available in these patients during periods of relapse and remission. We report observations in 58 children (mean age 10.1 years) with nephrotic syndrome and normal glomerular filtration rate. Hypocalcemia, modest hyperparathyroidism, and strikingly low calcidiol levels were identified during episodes of relapse. Most alterations were transient, and normalized on remission. The plasma concentration of calcitriol, the most active metabolite of vitamin D, was found to be normal in both relapse and remission. In the presence of hypocalcemia and hyperparathyroidism, however, normal plasma calcitriol levels in relapse may be inappropriately low and reflect a state of relative deficiency. Concurrent glucocorticoid therapy did not modify the results. A corollary of our observations is that children with relapsing or protracted nephrotic syndrome are at risk of developing metabolic bone disease, even without impairment of glomerular filtration rate.

The value of serum 25-hydroxyvitamin D measurements in hypoparathyroid and pseudohypoparathyroid patients treated with calciferol

In 23 patients with hypoparathyroidism or pseudohypoparathyroidism treated with vitamin D, and in whom the dosage was adjusted downward or upward in response to hypercalcemia or hypocalcemia respectively, assays of serum 25-hydroxyvitamin D (25-OHD) were carried out in addition to the usual serum calcium assays. In 120 assays there was a significant correlation between serum 25-OHD levels and serum calcium levels (corrected for serum albumin). There was, however, no clear distinction between the 25-OHD levels of patients who were hypocalcemic, normocalcemic or hypercalcemic. The highest serum 25-OHD level found in a hypocalcemic patient was 1193 nmol/L and the lowest serum 25-OHD level found in a hypercalcemic patient was 605 nmol/L. It was not possible to predict subsequent episodes of hypocalcemia or hypercalcemia from the serum 25-OHD levels. The 25-OHD assay was found to be useful only in checking compliance. We conclude that the assay of serum 25-OHD is of no more value than serum calcium alone in the management of compliant patients.

Low serum osteocalcin levels in glucocorticoid-treated asthmatics

Serum osteocalcin (OC) levels were measured in 19 asthmatic patients receiving long term glucocorticoid therapy and in age- and sex-matched asthmatic patients not receiving this treatment. In the glucocorticoid-treated patients, the mean OC level was approximately 50% less than that in the control group (P less than 0.001), and there was a direct correlation between serum OC and 1,25-dihydroxyvitamin D [1,25-(OH)2D; r = 0.71; P less than 0.001]. Multiple regression analysis in a total of 39 glucocorticoid-treated patients indicated that OC correlated directly to 1,25-(OH)2D and inversely to glucocorticoid dose. There was no correlation between OC and 1,25-(OH)2D in the control group and no significant difference in mean serum 1,25-(OH)2D between the steroid-treated asthmatic patients and the asthmatic control patients. The effect of a 4-day course of oral 1,25-(OH)2D on serum OC was studied in six patients with glucocorticoid excess and six normal subjects. There was a similar percent increase in OC levels in both groups, though the basal concentrations and absolute increases were substantially less in the steroid-treated group. It is likely that the depression of serum OC in glucocorticoid-treated patients results from the reduction in the rate of bone formation induced by these hormones.

Vitamin D metabolites in idiopathic infantile hypercalcaemia

Metabolites of vitamin D were measured in plasma from 83 patients with idiopathic infantile hypercalcaemia syndrome who were mentally handicapped but had normal calcium values at the time of the study. No significant difference was detected in the mean plasma concentrations of 25-hydroxyvitamin D2, 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D3, or 25,26-dihydroxyvitamin D3 between patients and age matched controls. The mean plasma concentration of 25-hydroxyvitamin D3 was significantly lower in patients than controls but this may be a secondary phenomenon related to less sunlight exposure. In addition, two hypercalcaemic patients with this syndrome were studied during the first year of life, and were found to have normal concentrations of vitamin D metabolites. These findings do not support a role for abnormal vitamin D metabolism in the pathogenesis of this syndrome.

Effect of race and diet on human-milk vitamin D and 25-hydroxyvitamin D

Vitamin D-deficiency rickets continues to be reported in infants fed human milk, and the importance of human milk as a source of vitamin D for infants is controversial. Furthermore, effects of race and of normally consumed maternal vitamin D intake on human-milk vitamin D have not been reported. Milk, serum, and three-day-diet diaries were obtained from 25 mother-infant pairs. Human-milk vitamins D3 and D2 and 25-hydroxyvitamin D3 were lower in blacks vs whites, whereas 25-hydroxyvitamin D2 did not differ. Total-milk vitamin D, but not 25-hydroxyvitamin D, correlated with vitamin D intake. Milk vitamin D2 specifically was correlated with vitamin D intake even after controlling for race. Infant serum 25-hydroxyvitamin D did not correlate with milk vitamin D or 25-hydroxyvitamin D; we speculate that the contribution of vitamin D from human milk in these infants is insignificant relative to the contribution from sunshine exposure.

Vitamin D prophylaxis in the elderly: a simple effective method suitable for large populations

A comparison of two regimens of vitamin D prophylaxis in elderly institutionalized subjects has been made. Sixty-six subjects received 2.5mg vitamin D2 by mouth in December 1982; a further group of 62 received the same dose in December 1982 and again in June 1983. Blood samples have been analysed for 25-hydroxyvitamin D2 [25(OH)D2] in 10 subjects from each group over a 12-month period. The serum 25(OH)D2 was maintained at normal concentrations for most of the year in the once-a-year dosage group but at the end of 12 months only 60% were fully protected. The twice-per-year regimen offered complete protection maintaining the serum 25(OH)D2 above the threshold associated with osteomalacia. It is concluded that a twice-yearly regimen of vitamin D supplementation is a practical method for prophylaxis in institutionalized elderly people.

Serial serum 25-hydroxyvitamin D and mineral homeostasis in very premature infants fed preterm human milk

Fourteen very low birthweight infants (mean +/- SD 1,070 +/- 180 g and 29.3 +/- 1.9 weeks gestation) fed their own mother's milk were clinically followed until 3-4 months of age with frequent measurements of serum calcium, phosphorus, magnesium, 25-hydroxyvitamin D (25-OHD), parathyroid hormone, alkaline phosphatase, and albumin, and urine calcium, phosphorus, and magnesium. These infants were matched for birthweight and gestation with 14 infants (1,075 +/- 152 g and 29.0 +/- 1.7 weeks) who had been similarly followed during concomitant studies of infants fed standard formula (Similac 20 cal/oz). Urine phosphorus was markedly lower in the breast milk-fed group from initiation of feedings, and serum phosphorus became significantly lower at and after 6 weeks of age. The fall in serum phosphorus was accompanied by a marked calciuria. Parathyroid hormone was suppressed in the breast milk-fed group, although serum calcium was not elevated and did not differ from formula-fed infants. A high incidence of moderate-severe hypomineralization on radiographs was seen in both breast milk- and formula-fed groups. Six of 14 breast-fed infants required phosphorus supplementation at 8-10 weeks of age because of significant hypophosphatemia, hypercalciuria, and hypomineralization. These infants differed from those not requiring phosphorus supplements by being smaller at birth but not of lower gestation, and having persistently low serum 25-OHD at and after 6 weeks of age.

Identification of 1,24(R)-dihydroxyvitamin D3-like bone-resorbing lipid in a patient with cancer-associated hypercalcemia

A lipid indistinguishable from 1,24(R)-dihydroxyvitamin D3 [1,24(R)-(OH)2D3] was found in serum and tumor extracts from a hypercalcemic patient with a small cell carcinoma of the lung. The lipid comigrated with authentic 1,24(R)-(OH)2D3 on high performance liquid chromatography using both straight and reverse phase columns and competed with tritiated 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3)] for binding to intestinal 1,25-(OH)2D3 receptor. Increasing doses of the lipid factor from tumor and authentic 1,24(R)-(OH)2D3 gave parallel responses in a bone resorption assay, as assessed by 45Ca release from prelabeled mouse calvaria. The lipid factor from the patient's serum and authentic 1,24(R)-(OH)2D3 had identical biological activities in the receptor binding and bone resorption assays. In addition, the mechanisms of action of this lipid factor and 1,24(R)-(OH)2D3 were indistinguishable. Bone resorption by both was inhibited by calcitonin, and neither the lipid factor nor authentic 1,24(R)-(OH)2D3 affected cAMP content in osteoblast-like bone cells derived from mouse calvaria. The estimated concentrations of the 1,24(R)-(OH)2D3-like lipid, expressed as 1,24(R)-(OH)2D3 were 11 ng/g tumor wet wt by the receptor binding assay and 9.2 ng/g tumor wet wt by the bone resorption assay. The mean serum concentration was 1.4 +/- 0.3 (+/- SD) ng/ml (n = 3) by the receptor binding assay. No activity was detected in either bioassay when extracts of nontumor tissues from this patient or tumor extracts and sera from one hypercalcemic and four normocalcemic cancer patients were tested. The mean serum 1,25-(OH)2D level was low (6.4 +/- 0.5 pg/ml; n = 2), and serum 1,24(R),25-(OH)3D in this patient was high (103 pg/ml) compared to normocalcemic cancer patients, in whom the mean serum 1,25-(OH)2D level was 27 +/- 12 pg/ml (n = 4) and the 1,24(R),25(OH)3D level was 28 +/- 1.3 pg/ml (n = 4). Thus, the 1,24(R)-(OH)2D3-like lipid may be a substrate for metabolic conversion to 1,24(R),25-(OH)3D in vivo. These results provide evidence for the presence of a novel metabolite of vitamin D3, 1,24(R)-(OH)2D3. Detection of this bone-resorbing lipid in both tumor and serum suggests, but does not prove, that the tumor secreted this bioactive lipid into the circulation and that the high level of circulating bone-resorbing lipid was related to the hypercalcemia in this patient.

Long-term control of plasma calcitriol concentration in dogs and humans. Dominant role of plasma calcium concentration in experimental hyperparathyroidism

Despite great interest in the elevated circulating levels of calcitriol (1,25-[OH]2D) associated with the clinical syndrome of human primary hyperparathyroidism, the relative potencies of known and potential stimuli/suppressors of long-term calcitriol levels have not been evaluated in either clinical or experimentally induced hyperparathyroid states. Based on reports that aparathyroid animals exhibit suppressed plasma calcitriol concentration and that acute administration of parathyroid hormone (PTH) to both humans and experimental animals or to renal slices in vitro results in increased plasma calcitriol concentration/production rate, it might be predicted that a chronic experimental model of either hypercalcemic primary hyperparathyroidism or hypocalcemic secondary hyperparathyroidism would show increased plasma calcitriol concentration. Chronic alterations in plasma calcium concentration have not been implicated as modulating calcitriol levels in any species. Accordingly, we investigated the long-term response of plasma calcitriol concentration in states of sustained experimental primary and secondary hyperparathyroidism. Intact dogs (group I) undergoing continuous intravenous PTH infusion for 12 d developed sustained hypercalcemia and hypophosphatemia, and plasma calcitriol concentration decreased from 23 +/- 3 to 14 +/- 3 pg/ml (P less than 0.01). Subsequent chelator (EGTA)-induced chronic normalization of hypercalcemia during ongoing PTH infusion resulted in a large and sustained increase in plasma calcitriol concentration to supernormal levels, reversible during subsequent cessation of chelator infusion. In additional intact dogs (group II), chronic chelator-induced hypocalcemic secondary hyperparathyroidism resulted in a sustained increase in plasma calcitriol concentration despite hyperphosphatemia. In normal human subjects undergoing a 12-13-d continuous intravenous PTH infusion to result in sustained moderate hypercalcemia (12.0 +/- 0.2 mg/100 ml) and hypophosphatemia, plasma calcitriol concentration decreased significantly (P less than 0.01) as in group I dogs and was followed by reversal to normal levels in a recovery period. The present results provide strong evidence in both humans and dogs that during experimentally induced chronic PTH excess, alterations in plasma calcium concentration dictate the directional response of circulating calcitriol concentrations. The long-term potency of plasma calcium concentration as a modulator of calcitriol metabolism is sufficient to override opposing modulation by plasma phosphorus concentration and PTH.

Late infantile tetany and secondary hyperparathyroidism in infants fed humanized cow milk formula. Longitudinal follow-up

Five full-term infants with birth weights appropriate for gestational age presented with hypocalcemic tetany at 5 to 9 days of age. All infants had been fed Similac 20, a cow milk formula. Initial mean serum calcium (Ca), phosphorus (P), and magnesium (Mg) levels of the tetanic infants were 6.8, 9.5, and 1.6 mg/dL, respectively. The mean serum parathyroid hormone (PTH) level was elevated at 79 mu LEq/mL (adult normal values, less than or equal to 57 mu LEq/mL). Following restoration of normocalcemia with Ca supplements, feeding was reinstituted with Similac 20 in two infants and Similac PM 60/40 in three infants. Serum biochemical and hormonal values were compared with those of 18 exclusively breast-fed infants followed up from three weeks to six months and 14 Similac 20-fed full-term infants followed up from one week to six months. In tetanic infants, serum Ca concentrations became elevated (10.4 +/- 0.05 mg/dL; mean +/- SEM) by six weeks (vs 9.2 +/- 0.3 mg/dL in breast-fed infants) (P less than .001) and serum Mg concentrations (2.26 +/- 0.01 mg/dL) by four weeks (vs 1.92 +/- 0.07 mg/dL in breast-fed infants) (P less than .01). Mean serum P concentrations declined progressively. Mean serum PTH concentrations were elevated and ranged from 74 to 143 mu LEq/mL at two to 16 weeks (vs mean 28 to 35 mu LEq/mL in breast-fed infants (P less than .0001). In 14 formula-fed-nontetanic full-term infants, serum PTH concentrations were intermediate between formula-fed-tetanic and breast-fed infants, mean serum Ca concentrations ranged from 10.2 to 10.4 mg/dL, and mean serum P concentrations declined from 8.3 to 7.1 mg/dL. We speculate that acute hypocalcemic tetany in the study infants was induced by the relatively high P load in cow milk formulas (vs human milk); with the continued P load, secondary hyperparathyroidism continued, maintaining P, Ca, and Mg homeostasis.

Magnesium administration reverses the hypocalcaemia secondary to hypomagnesaemia despite low circulating levels of 25-hydroxyvitamin D and 1,25-dihydroxy vitamin D

The effect of parenteral administration of magnesium was studied in five patients with hypomagnesaemic hypocalcaemia. The initial metabolic state was characterized by a normal level of serum immunoreactive parathyroid hormone (iPTH), and by low or undetectable serum 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25 (OH)2D). A parathyroid response was elicited by the acute intravenous injection of magnesium chloride. In contrast, 1,25(OH)2D did not change up to 24 h after the injection. Intramuscular magnesium sulphate restored serum magnesium and calcium to normal, whereas iPTH was transiently increased. 25OHD remained low and unchanged. 1,25(OH)2D rose very slowly, but the correction of hypocalcemia began before any change in 1,25(OH)2D levels could be demonstrated. Thus, the early correction of hypocalcemia mainly depended on the restoration of an adequate parathyroid function independently of the secretion of 1,25(OH)2D.

Different metabolism of vitamin D2 and vitamin D3 in epileptic patients on carbamazepine

Serum concentrations of vitamin D metabolites were measured in 30 epileptic outpatients on monotherapy with carbamazepine before and during treatment with either vitamin D2 or vitamin D3, 4000 IU per day for 24 weeks. Vitamin D2 treatment increased the serum concentration of 25OHD2, but a corresponding decrease in 25OHD3 resulted in an unchanged serum value of total 25OHD. Vitamin D3 treatment increased the serum concentration of 25OHD3. The resulting serum level of 25OHD was consequently twice the level of that in the D2-treated group. The serum concentrations of the dihydroxy metabolites showed a similar difference between the 2 treatment groups. We conclude that treatment with vitamins D2 and D3 in the same doses produces considerably different serum concentrations of vitamin D metabolites. If the present findings can be extrapolated to normal subjects, it is important to consider more carefully which D-vitamin should be used, both with regard to therapy and supplementation.

The relations between vitamin D2 and D3 in the diet and plasma 25OHD2 and 25OHD3 in elderly women in Great Britain

Vitamin D2 and D3 intake and plasma 25OHD2 and 25OHD3 were measured in 70 elderly women; 13 living at home and 57 long-stay patients with no access to sunlight. Vitamin D2 intake and plasma 25OHD2 were correlated in the whole group (p less than .005) and vitamin D3 intake and plasma 25OHD3 and total D intake and total 25OHD were significantly correlated (p less than .005) in the patients. In the whole group the plasma 25OHD2 increased by 4.5 nmol/l for every 1 microgram increase in vitamin D2 intake. This was also the increase observed in a longitudinal study of vitamin D2 supplements in 11 patients. Vitamin D intake is a significant determinant of plasma 25OHD and the relation between them suggests that stores of vitamin D can be maintained at 20 nmol/l in the elderly by a daily intake of 4 micrograms of vitamin D, even in the absence of sunlight.

Vitamin D metabolism in patients intoxicated with ergocalciferol

Vitamin D metabolites were measured on admission in eight patients intoxicated with ergocalciferol (serum calcium 3.01-4.05 mmol/l) and also during the subsequent 2 months in six of the eight. Serum concentrations of 25-hydroxyergocalciferol, on admission, were grossly elevated in all patients (range 583-1843 nmol/l). Serum calcium concentration was related significantly only to the concentration of 25-hydroxyergocalciferol (P = 0.003). Concentrations of 25-hydroxyergocalciferol in serum were significantly related to those of calciferol (P = 0.004). Elevated initial concentrations of 1,25-dihydroxycalciferol, mainly as 1,25-dihydroxyergocalciferol, were found in seven of the eight patients (range 179-313 pmol/l). It is suggested that the hypercalcaemia in these patients may be explained by the action of 25-hydroxyergocalciferol at high concentration in competing for 1,25-dihydroxycalciferol receptors, thus exerting a biological effect per se, and also by increasing the synthesis of 1,25-dihydroxycalciferol through a mass-action effect on the renal 1 alpha-hydroxylase.

The effect of intramuscularly administered vitamin D3 on serum vitamin D metabolites and electrolytes in vitamin D3 deficient dairy cows

The effect of intramuscular administration of vitamin D₃ (1×10⁶ IU D₃/100 kg bodyweight) to 3 different dairy breeds on the serum levels of vitamin D₃, 25-OH-D₂, 25-OH-D₃, Ca, inorganic P and Mg was studied.

The vitamin metabolites and the electrolytes were analysed on 9 occasions during a 36-day period. Vitamin D₃ was analysed on 6 occasions during the same period. No significant breed differences were observed except for 25-OH-D₃ (P ≤ 0.05). The D₃ level rose in 1 day from < 2 ng/ml to 906 ng/ml and decreased to below 50 % of the peak level after 6 days. At the end of the experiment (day 36) vitamin D₃ was < 2 ng/ml. 25-OH-D₃ rose from < 2 ng/ml to 106 ng/ml in 6 days and stayed at this level during the whole experiment. 25-OH-D₂ decreased from 16 ng/ml to 5 ng/ml during the observation period.