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.

Vitamin D metabolites in adolescents and young adults with cystic fibrosis: effects of sun and season

To assess mineral metabolism in patients with cystic fibrosis and to study the effects of season and sunlight exposure on generation of vitamin D metabolites, we quantified serum levels of calcidiol and calcitriol, other measures of bone metabolism, and radiographic bone mass in 20 adolescents and young adults with CF and 20 age-matched normal volunteers. Levels of calcidiol were lower in patients with CF than in controls and lower in Massachusetts than in Arizona in both study groups. Controls in Arizona had higher (P less than 0.05) levels of calcitriol than in Massachusetts throughout the year. All control subjects in both states had higher levels of calcitriol than did patients with CF. Patients in Massachusetts had significantly lower levels of calcitriol in winter than in summer. Summer levels of calcitriol in CF were significantly higher in Massachusetts than in Arizona; during winter, lower levels were found in Massachusetts than in Arizona. Mean bone density in patients with CF was 88% and 89% of normal American standards in Massachusetts and Arizona, respectively. These data indicate a seasonal, sunlight-related influence on levels of vitamin D metabolites in patients with CF receiving approximately 1000 IU vitamin D per day. Older patients with CF with progressively diminishing sunlight exposure may be at increased risk for development of osteopenia. The detected radiographic abnormalities of bone mineralization may also be related to malabsorptive deficiencies of calcium and phosphorus.

The effect of trauma on serum concentrations of vitamin D metabolites in patients with hip fracture

In a previous study we observed lower serum concentrations of 25(OH)D, 24,25(OH)2D, and 1,25(OH)2D in patients with hip fracture than in aged control subjects. In order to evaluate the effect of trauma on vitamin D metabolite levels, we measured serum concentrations of vitamin D binding protein (DBP) in 118 patients with hip fracture and 71 aged control subjects. Serum DBP was lower in the patients than in the controls (mean +/- SD 315 +/- 60 vs 371 +/- 44 mg/l, P less than 0.001). Serum DBP correlated positively with serum total protein, albumin, alpha 2-globulin, and the vitamin D metabolite levels in the patients. When correcting for differences in serum DBP, serum 25(OH)D and 24,25(OH)2D still were significantly lower in patients than in controls, whereas serum 1,25(OH)2D was not. The free 1,25(OH)2D index (10(5) x molar ratio 1,25(OH)2D/DBP) was lower in patients than in controls, but the level of significance was marginal. This difference was not significant when patients and controls with impairment of renal function were excluded. It is concluded that the difference in serum 25(OH)D and 24,25(OH)2D between patients and controls is largely preexistent. However, the lower serum 1,25(OH)2D in the patients is mainly caused by the trauma. The free 1,25(OH)2D concentrations are almost similar in the two groups when renal function is normal.

Can the fetus regulate its calcium uptake?

To investigate the role of the fetus in vitamin D metabolism concentrations of vitamin D metabolites, 25(OH)D, 24,25(OH)2D and 1,25(OH)2D, were measured in human umbilical artery and vein. There were no differences between artery and vein in 25(OH)D and 24,25(OH)2D levels. 1,25(OH)2D concentrations were statistically significantly higher in the artery than in the vein. It has been shown in animal experiments that 1,25(OH)2D is an important factor in the maintenance of the placental calcium gradient. We suggest that the fetus actively produces 1,25(OH)2D and hence has the capacity to control its calcium influx.

Relative contributions of diet and sunshine to the overall vitamin D status of the grazing ewe

Circulating concentrations of 25-hydroxyvitamin D2 (25OHD2) and 25-hydroxyvitamin D3 (25OHD3) provide, respectively, a measure of the contributions of the diet and sunshine to the overall vitamin D status. These indices were measured in grazing sheep over a 16 month period which included their first pregnancy. Seasonal fluctuations in 25OHD3 concentrations were very marked, demonstrating both the dominance of photobiosynthesis as a source of vitamin D in the summer and also the lack of an effective storage mechanism. The concentration of 25OHD2 was subject to much smaller fluctuations, but when young grass was being consumed it was significantly lower than when mature grass or hay was fed. Supplementation in winter maintained circulating concentrations at a satisfactory level and may be a wise precaution in practice.

25-Hydroxyvitamin D and 1,25-dihydroxyvitamin D of D2 and D3 origin in maternal and umbilical cord serum after vitamin D2 supplementation in human pregnancy

Serum concentrations of 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D [1,25-(OH)2D] of vitamin D2 and D3 origin were determined separately in 10 women before vitamin intake in early pregnancy, and repeated in maternal and cord serum obtained at delivery after 20 to 30 wk of vitamin D2 supplementation in a dose of 400 IU/day. Before supplementation 25-OHD2 and 1,25-(OH)D2D2 were present in just traceable or nondetectable concentrations, but the levels increased in all to a mean +/- 1 SD of 7.3 +/- 3.7 ng/ml and 37.2 +/- 18.1 pg/ml, respectively (p less than 0.0025), by the time of delivery. At delivery the total 25-OHD and 1,25-(OH)2D levels were always lower in the cord than in the maternal serum (30.7 +/- 14.2 versus 20.1 +/- 9.1 ng/ml, and 90.1 +/- 31.2 versus 37.3 +/- 11.6 pg/ml, p less than 0.0025). The paired concentrations of 25-OHD were closely related (r = 0.89, p less than 0.0005), while the association for 1,25-(OH)2D was not statistically significant (r = 0.53, p less than .01). The 25-OHD of D2 and D3 origin accounted for a similar proportion of the total 25-OHD in the maternal and cord serum (ratio of 25-OHD2 to 25-OHD3: 0.40 +/- 0.28 versus 0.45 +/- 0.29, p = NS), as did the respective 1,25-(OH)2D metabolites [ratio of 1,25-(OH)2D2 to 1,25-(OH)2D3: 0.73 +/- 0.35 versus 0.90 +/- 0.50, p = NS].(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in clinical settings

A quick and simple method for the selective measurement of 25-hydroxyvitamin D3 (25OHD3) and 25-hydroxyvitamin D2 (25OHD2) is described. It includes a rapid sample preparation technique and a combination of a selective radioimmunoassay for 25OHD3 and a competitive protein-binding assay using vitamin D-binding protein for the determination of total 25OHD, including 25OHD3 and 25OHD2. The method was compared with a procedure which include methanol/methylene chloride extraction and chromatography on Sephadex LH 20, and a procedure which includes HPLC and final quantification by u. v. detection. The methods were applied to three groups of patients in order to obtain information on how far assay procedures could be simplified for use in the clinical settings. It is concluded that the method described is applicable for following patients on vitamin D2 therapy. When groups of patients have to be compared, the mean values of the estimates are comparable, whether a simple method or a laborious method is used. Hence, the selection of assay method should take into account the clinical problem and the cost of the analysis.

Evidence that 1,25-dihydroxyvitamin D3 inhibits the hepatic production of 25-hydroxyvitamin D in man

Previous in vitro studies in rachitic rat liver suggested that 1,25-dihydroxyvitamin D inhibits the hepatic production of 25-hydroxyvitamin D (25-OHD). An investigation therefore was carried out in eight normal subjects to determine whether concomitant administration of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] would alter the response of serum 25-OHD to challenge with vitamin D. In control studies, vitamin D, 100,000 U/d for 4 d, significantly increased mean serum 25-OHD, from 26.3 +/- 2.9 to 66.7 +/- 12.6 ng/ml (P less than 0.01). In contrast, 1,25(OH)2D3, 2 micrograms/d for 4 d, completely prevented an increase in serum 25-OHD in response to the same dose of vitamin D in the same individuals (25.1 +/- 2.2 vs. 27.4 +/- 5.3 ng/ml, NS). In a post-control study in seven of the normal subjects, vitamin D again significantly increased mean serum 25-OHD, from 18.2 +/- 3.1 to 42.8 +/- 4.7 ng/ml (P less than 0.001). In each of the three studies, mean serum calcium, phosphorus, and creatinine did not change and remained within the normal range. Whereas mean urinary calcium did not change in response to vitamin D alone during the 4 d of the two control studies, it increased significantly in the study in which vitamin D and 1,25(OH)2D3 were given together. A dose-response inhibition of the response of serum 25-OHD to vitamin D by 1,25(OH)2D3 was demonstrated in two of the normal subjects. The results provide evidence that 1,25(OH)2D3 inhibits the hepatic synthesis of its precursor 25-OHD in man.

Evaluation of the total fetomaternal vitamin D relationships at term: evidence for racial differences

The present study assessed the total fetomaternal vitamin D relationship at term in 12 white and 10 black mothers and their infants. Antirachitic sterols were extracted from plasma, chromatographed, and finally quantitated using competitive protein binding assays. Compounds quantitated included vitamins D2 and D3, 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2, 24,25-dihydroxyvitamin D3, 25,26-dihydroxyvitamin D3, 1,25-dihydroxyvitamin D2, and 1,25-dihydroxyvitamin D3. There was a strong correlation between maternal and neonatal plasma concentrations of all antirachitic sterols measured with the exception of vitamins D2 and D3. Vitamins D2 and D3, although detectable in maternal plasma, were undetectable in neonatal plasma. Racial comparisons demonstrated that vitamin D3, 25-hydroxyvitamin D3, 24,25-hydroxyvitamin D3, and 25,26-(OH)2-D3 were significantly (P less than 0.05) higher in white than in black mothers. Total 25-hydroxyvitamin D and 24,25-hydroxyvitamin D were also significantly (P less than 0.05) higher in white than in black mothers. A similar pattern was found in black and white infants except for 25,26-(OH)2-D3. Black mothers and their infants had significantly (P less than 0.05) higher 1,25-hydroxyvitamin D3 compared to the white subjects, although total 1,25-hydroxyvitamin D was not different between races. No significant racial (P greater than 0.05) differences were found for any of the vitamin D2 compounds. The results support the concept that fetomaternal vitamin D status are intimately related. Further, they strongly suggest that fetal metabolism begins with 25-hydroxyvitamin D rather than vitamin D. Finally, racial factors appear to influence the overall vitamin D status of both mother and fetus, and may influence antirachitic sterol metabolism.

Persistence of parathyroid hypersecretion after vitamin D treatment in Asian vegetarians

An investigation into plasma calcium concentrations and the biochemical factors which regulate it in vegetarian Asian subjects without clinical or radiological features of osteomalacia revealed the presence of low serum 25-hydroxyvitamin D concentrations and elevated PTH concentrations, even in the presence of calcium levels in the normal range (up to 2.35 mmol/liter). These elevated PTH concentrations, though not as high as those in osteomalacic patients with hypocalcemia, often persisted despite treatment with vitamin D, normalization of 25-hydroxyvitamin D, and an increase in calcium concentrations. In one patient the PTH concentration remained high even when the plasma calcium concentration became supranormal. Therefore, secondary hyperparathyroidism is commonly associated with vegetarianism, and may play an important role in maintaining calcium concentrations within the normal range. Persistent elevation of PTH despite normalization of 25-hydroxyvitamin D also points to autonomous PTH hypersecretion, which may result in osteolysis in the long term, and raises the question of the need for vitamin D supplementation in vegetarians with low dietary intake of vitamin D.

Defective photoproduction of cholecalciferol in normal and uremic humans

The initial step in cholecalciferol (vitamin D3) metabolism is the photo-conversion of 7-dehydrocholesterol to previtamin D3. This reaction occurs in the epidermis and requires ultraviolet light. We measured the circulating concentration of vitamin D (ergocalciferol and cholecalciferol), 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D in 14 normal white, 9 normal black subjects, and in 9 white and 17 black hemodialysis patients. The mean plasma vitamin D in normal white subjects was greater than in normal black subjects, 4.01 +/- 1.02 ng/ml versus 0.96 +/- 0.30 ng/ml, respectively (P less than 0.05). Plasma 25-hydroxyvitamin D in normal blacks was also less than in normal whites, 17.7 +/- 1.5 ng/ml versus 31.3 +/- 3.0 ng/ml, respectively (P less than 0.01). In uremic white subjects, plasma vitamin D, 6.7 +/- 2.6 ng/ml, was similar to normal white subjects. However, vitamin D was not detectable in 12 of 17 uremic black subjects and was depressed in the remainder of the group. Following exposure to a single minimal erythema dose of ultraviolet-B irradiation, the maximal increase in plasma vitamin D was depressed in white dialysis patients as compared to healthy white subjects, 6.3 +/- 1.9 ng/ml versus 21.3 +/- 2.8 ng/ml, respectively (P less than 0.02). 7-Dehydrocholesterol content was similar in epidermis from site-matched skin of fresh cadavers and white hemodialysis patients, 131 +/- 23 ng/mg versus 124 +/- 14 ng/mg skin, respectively. It is concluded that chronic hemodialysis patients exhibit defective photoproduction of cholecalciferol, despite normal epidermal content of substrate, 7-dehydrocholesterol.

Interlaboratory comparison of 25-hydroxyvitamin D determination

This interlaboratory study on determination of 25-hydroxyvitamin D (25-OH-D) in serum involved 15 laboratories in eight European countries. All could distinguish between normal (50 +/- 31 nmol/L, mean +/- SD) and grossly increased concentrations, but for eight laboratories the results for serum samples with low and normal 25-OH-D content overlapped. In general, values were well reproducible, but interlaboratory variation in 25-OH-D measurement was large, 24,25(OH)2D3 interfering in most of the assays. We present evidence in favor of chromatography before assay, as opposed to nonchromatographic methods. Liquid chromatography with ultraviolet detection for quantifying 25-OH-D2 and 25-OH-D3 appears to be an appropriate reference method, whereas competitive protein binding assay is the method of choice for routine determinations. Control sera with subnormal, normal, and above-normal concentrations of 25-OH-D3 are needed for use in standardization of 25-OH-D assays.

The contribution of dietary vitamin D and sunlight to the plasma 25-hydroxyvitamin D in the elderly

Total plasma 25-hydroxyvitamin D (25-OHD) and its components 25-OHD2 and 25-OHD3 were measured during the winter in young and elderly healthy persons and in elderly women patients in a long-stay mental hospital. The long-stay patients had no exposure to sunlight or other ultraviolet irradiation, but their diet alone maintained an average total 25-OHD level of 16 nmol/l (range, 10.3-26.5 nmol/l), with most values within the ranges observed in the other two groups, although the average value was lower. The plasma 25-OHD2 which is derived exclusively from vitamin D2 in the diet was similar in all three groups and the vitamin D intake was also similar in the two elderly groups. 25-OHD3 is obtained from the diet as well as from the skin and in the elderly patients the diet alone maintained equal concentrations of 25-OHD2 and 25-OHD3. These findings taken together suggest that the diet accounted for 70 per cent of the total 25-OHD in the active elderly in winter compared with 50 per cent in the young subjects. In all our subjects, young or old, the diet was the major source of vitamin D.

Vitamin D nutrition in pregnant women at term and in newly born babies in Saudi Arabia

A survey to assess the vitamin D nutritional state in 119 pregnant women at term and in their newborns was undertaken in Riyadh, Saudi Arabia. Concentrations of 25-hydroxy vitamin D (25-(OH)D) were below 4 ng/ml in 30 of 119 maternal sera, in 11 of which they were undetectable. The median concentration of 25-(OH)D was 5.7 ng/ml, which is comparable to that found in Asian vegetarian women at term in London. Fifty of 119 cord samples had undetectable 25-(OH)D, and a total of 81 samples had 25-(OH)D concentrations of less than 4 ng/ml. Despite the low 25-(OH)D concentrations cord bloods had calcium concentrations higher than those in maternal blood, while serum albumin concentration was similar in maternal and cord samples. Higher socioeconomic background of women, antenatal care, and vitamin D supplementation were associated with significantly higher concentrations of 25-(OH)D. Vitamin D supplementation, however, had no significant effect on 25-(OH)D concentration in cord samples or on the weight of the newborns. This study shows the high prevalence of marginal vitamin D nutrition in women in Saudi Arabia, which may predispose babies to rickets during infancy. In a country endowed with plentiful sunshine, the exclusion of sunshine by thick dark veils and bad housing probably contribute to this marginal state of vitamin D nutrition.

Effect of nutrition on vitamin D status: studies on healthy and poorly nourished Brazilian children

A cross-sectional study was carried out of 412 healthy and 226 chronically malnourished children in Recife, Brazil. Anthropometric measurements, x-rays of hands and wrists, and biochemical data related to skeletal growth were obtained. Levels of plasma 25 hydroxyvitamin D were measured in both groups of children and both showed higher concentrations than those reported for normal European children. The high levels of 25 hydroxyvitamin D found in these two groups of Brazilian children are probably the result of the intense solar radiation in this part of Brazil and argue against the diet being an important source of vitamin D in poorly nourished children. Some bone abnormalities were seen in the underprivileged group of children but in view of our findings these were more likely to be a result of protein-energy malnutrition than rickets.

An international comparison of vitamin D metabolite measurements

An international 19-laboratory survey was organized to compare assays for 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, and 1,25-dihydroxyvitamin D in plasma. Each participant received two ethanolic standard solutions of each metabolite and eight plasma samples. Each laboratory used its usual procedures. Mean interlaboratory coefficients of variation (CVs) for the eight plasma samples were 35%, 43%, and 52% for 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, and 1,25-dihydroxyvitamin D, respectively. Average CVs for the standard solutions were 27%, 23%, and 25%, respectively. Of the eight plasma samples, five had the same concentration for one of the metabolites. One sample was diluted to 0.6 times its original concentration and three samples were fortified with one or more of the metabolites under investigation. Fourteen of 18 laboratories (78%) could distinguish between the five unchanged samples and the modified ones with their 25-hydroxyvitamin D assay. Nine of 12 (75%) could distinguish the modified samples from the other samples with the 24,25-dihydroxyvitamin D assay. Only eight of 15 (53%) could do this their 1,25-dihydroxyvitamin D assay. Values from different laboratories evidently cannot be intercompared without making an actual comparison of the assay procedures. Furthermore, in case of clinical applications of these assays, each laboratory should establish its own reference values and should continually use an internal reference sample to assess the precision of the procedures.

Phosphate deprivation increases serum 1,25-(OH)2-vitamin D concentrations in healthy men

To re-evaluate whether phosphate-deprivation alters serum 1,25-(OH)2-D concentrations in men, we measured serum 1,25-(OH)2-D levels in seven healthy men while they ate constant diets providing 52.2 +/- 4.3 sd mmoles PO4/day for 12 days and then while they ate a diet providing 29.4 +/- 6.0 mmoles PO4/day and also were given Al(OH)3 for 18 days. Serum PO4 levels fell only transiently. Net intestinal PO4 absorption became indistinguishable from zero but, because of renal PO4 conservation, PO4 balances did not change. Nevertheless, serum 1,25-(OH)2-D concentrations increased from 80 +/- 21 pM during control to 104 +/- 26 pM; during PO4 deprivation; P less than 0.01. Net intestinal calcium (Ca) absorption tended to rise during PO4 deprivation, the individual increments being correlated to the increments in serum 1,25-(OH)2-D concentrations (r = 0.78; P less than 0.05). Urinary Ca excretion rose; P less than 0.001, the increments exceeding the increments in net intestinal Ca absorption so that Ca balances became more negative; P less than 0.001. Urinary hydroxyproline excretion did not change. Thus, as in women and animals, PO4 deprivation appears to cause enhanced net bone resorption apparently by reducing bone formation.

Effects of weight loss on serum 1,25-(OH)2-vitamin D concentrations in adults: a preliminary report

During a review of 42 metabolic studies in healthy women and men we observed that serum 1,25-(OH)2-D concentrations were directly correlated to the observed daily changes in body weight (r = 0.68; P less than 0.001) and to caloric intake/kg/day (r = 0.39; P = 0.01). These relationships could not be accounted for by related and physiologically expected changes in serum Ca or iPTH concentrations. However, serum 1,25-(OH)2-D concentrations were observed to be inversely correlated to serum PO4 levels (r = -0.44; P = 0.004). In addition, serum PO4 levels were inversely correlated to the daily changes in body weight (r = -0.40; P = 0.009). Since dietary sodium intake averaged 142 mmol/day, it is unlikely that the observed changes in weight were the result of changes in salt and water balance. Thus it seems reasonable to speculate that serum 1,25-(OH)2-D concentrations may vary directly with energy balance, as reflected by changes in body weight. This effect may be mediated by alterations in PO4 metabolism. The accurate assessment of serum 1,25-(OH)2-D levels thus appears to require several measurements over time periods during which body weight is stable.