Vitamin D Status Research Articles

Calcium absorption measured by stable calcium isotopes ((42)Ca & (44)Ca) among Northern Chinese adolescents with low vitamin D status.

An adequate calcium intake and vitamin-D status is important for bone mineralization in adolescents. In Northern China, calcium intake and plasma vitamin-D level of adolescents is low due to low consumption of dairy foods and inadequate sunshine exposure. True fractional calcium absorption (TFCA) in Chinese adolescents has never been performed. This study aims to evaluate nutritional adaptation namely, TFCA and urinary calcium excretion among Chinese adolescents in northern China.

Use of Stable Calcium Isotopes (42Ca & 44Ca) in Evaluation of Calcium Absorption in Beijing Adolescents with Low Vitamin D Status

Female adolescent populations with low calcium intakes and sub-optimal vitamin D status are found in northern China. Whether these individuals are able to adapt by enhancing calcium absorption and reducing calcium excretion for maximizing calcium retention is unknown. This study examined the association between true-fractional-calcium-absorption (TFCA), plasma 25-hydroxy-vitamin-D, and urinary calcium excretion among adolescents in Northern China. Twelve healthy girls 9 to 17 years old were recruited from Beijing during a winter. Calcium intake, anthropometry, pubertal status, plasma 25-hydroxyvitamin-Ds (25-OHD), serum calcium, and urinary calcium were determined. TFCA was evaluated by dual stable calcium isotopes. The mean +/- SD calcium intake, 24-hour urinary calcium excretion, plasma 25-OHD and TFCA were 591 +/- 164 mg/day, 79.9 +/- 49.6 mg/day, 30.5 +/- 9.8 nmol/L, and 60.4 +/- 14.4%, respectively. TFCA was inversely correlated with 25-OHD (r = -0.73, p = .008). Urinary calcium was correlated with the onset of menarche (r = 0.63, p = .027). Post-menarcheal girls had a higher urinary calcium output than premenarcheal girls (p = .03). Adolescents from north China with sub-optimal vitamin-D status are able to adapt by enhancing TFCA and reducing urinary calcium excretion to retain calcium for bone development. TFCA was inversely correlated with plasma 25-OHD. Whether a higher efficiency of calcium absorption is sustainable if the shortfall of vitamin D persisting remains to be studied.

Serum 25-hydroxyvitamin D levels in active women of middle and advanced age in a rural community in Japan.

There have been few epidemiologic studies on vitamin D status in Asians. The purpose of this study was to investigate the 25-hydroxyvitamin D (25[OH]D) levels in active women of middle and advanced age in Japan. We targeted 236 women who participated in an annual health check-up program in September 1997. Among them, 160 women were examined. Serum 25(OH)D2 and 25(OH)D3 levels were determined with high-performance liquid chromatography. In addition, the study included survey questions regarding age, body weight and height, occupation, use of skin protection, clinical and reproductive histories, and lifestyles. The average age was 65.6 y (SD = 8.3). The mean concentrations of 25(OH)D2 and 25(OH)D3 were 0.5 (SD = 3.2) nmol/L and 78.3 (SD = 17.8) nmol/L, respectively. None of the subjects showed hypovitaminosis D (25[OH]D < 37.0 nmol/L). Concentrations of 25(OH)D3 did not change with age (r = -0.079, P = 0.32), nor did other variables associated with 25(OH)D3 concentrations except for "engaging in farming" (P = 0.03) in the occupational category. These findings indicate that 25(OH)D levels in active middle- and advanced-aged women in Japan have appropriate vitamin-D status. Studies to elucidate and assess the dietary intake of vitamin D in Japanese women can be of further benefit.

Regulation of myosin isozyme expression by vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 in the rat heart

In this report, we demonstrate a significant inverse correlation between contractility and serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] levels and no correlation between contractility and serum levels of calcium, phosphate, or PTH. We also examined myosin isozyme distribution in vitamin D3-deficient rats, because myosin isozyme distribution can alter contractility. There was a significant increase in the levels of the V1 myosin isozyme in animals raised on a vitamin D3-deficient diet that maintained normal serum calcium and phosphate levels. There was no difference in the relative myosin isozyme distribution in animals raised on a hypocalcemia-yielding vitamin D3-deficient diet vs. animals raised on a control diet. As increased contractility has been observed in both groups of vitamin D3-deficient animals, a shift in myosin isozyme distribution cannot solely explain the increase in contractility previously observed in the vitamin D3-deficient rat heart. To determine whether 1,25-(OH)2D3 directly regulates myosin isozyme levels, we analyzed myosin isozyme distribution in primary cultures of ventricular myocytes. We found that 1,25-(OH)2D3 reduces total myosin levels, but does not alter myosin isozyme distribution. Thus, we show that the influence of vitamin D3 status on myosin isozyme expression in the intact rat involves a complex regulatory system of direct and indirect effects.

Regulation of myosin isozyme expression by vitamin D3 deficiency and 1,25-dihydroxyvitamin D3 in the rat heart.

In this report, we demonstrate a significant inverse correlation between contractility and serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] levels and no correlation between contractility and serum levels of calcium, phosphate, or PTH. We also examined myosin isozyme distribution in vitamin D3-deficient rats, because myosin isozyme distribution can alter contractility. There was a significant increase in the levels of the V1 myosin isozyme in animals raised on a vitamin D3-deficient diet that maintained normal serum calcium and phosphate levels. There was no difference in the relative myosin isozyme distribution in animals raised on a hypocalcemia-yielding vitamin D3-deficient diet vs. animals raised on a control diet. As increased contractility has been observed in both groups of vitamin D3-deficient animals, a shift in myosin isozyme distribution cannot solely explain the increase in contractility previously observed in the vitamin D3-deficient rat heart. To determine whether 1,25-(OH)2D3 directly regulates myosin isozyme levels, we analyzed myosin isozyme distribution in primary cultures of ventricular myocytes. We found that 1,25-(OH)2D3 reduces total myosin levels, but does not alter myosin isozyme distribution. Thus, we show that the influence of vitamin D3 status on myosin isozyme expression in the intact rat involves a complex regulatory system of direct and indirect effects.

Vitamin D status of children and adolescents of African and Asian diplomats in Germany

Vitamin D-deficiency has been observed among immigrant children with rickets and osteomalacia in Western Europe. So vitamin D-status in 34 children and juveniles (17 girls, 17 boys) of African and Asian diplomats staying in West Germany only for a certain time is examined. During summer 1989 plasma levels of alkaline phosphatase, calcium, phosphate, 25-hydroxy-cholecalciferol and 1,25-dihydroxycholecalciferol is measured. According to their native country the subjects are divided into three groups: I North Africa (n = 7), II Central Africa (n = 18), III Asia (n = 9). No clinical signs of rickets or osteomalacia are detected. All plasma levels of calcium and phosphate are in the normal range so as most of the values of the alkaline phosphatase. In Group I 85.7% (n = 6), group II 77.8% (n = 14) and group III 44.4% (n = 4) have decreased values of 25-OHD whereas most strikingly elevated amounts of 1,25-OH2D are measured in 57.1% (n = 4) of the subjects in group I, 66.7% (n = 12) in group II and 11.1% (n = 1) in group III. Normal values for both 25-OHD and 1,25-OH2D are rare: one case (11.1%) in group I, no case in group II, four cases (44.4%) in group III. The influence of the time staying in West Germany on vitamin D-status, a possible dietary lack due to inadequate nutrition, the role of skin pigmentation and a potential genetic abnormality of vitamin D-metabolism is discussed to explain the results.

Effect of Vitamin C, Environmental Temperature, Chlortetracycline, and Vitamin D3 on the Development of Tibial Dyschondroplasia in Chickens

Seven experiments were conducted to test the influence of dietary supplementary ascorbic acid on the development of tibial dyschondroplasia in broiler chickens. Ascorbic acid supplementation significantly reduced the incidence and number of birds with a large mass of cartilage in the tibia in the first experiment but not in the two subsequent experiments. Because environmental temperature, microbial infection, and vitamin D3 status had been reported in the literature to influence ascorbic acid metabolism in the chicken, experiments were conducted to see if these variables could influence supplemental ascorbic acid effects on development of tibial dyschondroplasia. Results of the experiments indicated that none of these factors influenced the effect of ascorbic acid on the development of tibial dyschondroplasia. The presence of vitamin D3 in the diet significantly influences the incidence of this disorder.

Changes in phosphate do not affect insulin release from isolated mouse islets of Langerhans.

Phosphate affects glucose tolerance, insulin release and peripheral insulin sensitivity. In the present study moderate changes in the phosphate concentration of the incubation medium from 0.3 to 2 mmol/l (i.e., within the physiological range) did not affect insulin release from isolated mouse islets in vitro. In addition, the vitamin-D status of the animals had no effect on the glucose-stimulated insulin response in the different phosphate concentrations. Therefore these data indicate that the impaired glucose tolerance seen in hypophosphatemic states is not due to a direct effect of phosphorus levels on the insulin-releasing B-cell.

Vitamin D and the immune system

The investigation of the potential influence of 1,25-(OH)2D3 on immune cells has expanded our understanding of hormone-cytokine interactions. 1,25-(OH)2D3 stimulates phenotypic and function changes in immature monocytes, alters protein synthesis, increases adherence, and augments interleukin-1 secretion. T lymphocyte proliferation and B cell immunoglobulin production are inhibited by the hormone. 1,25-(OH)2D3 decreases IL 2 and IFN-gamma synthesis by activated T lymphocytes in association with decreases in mRNA for these proteins. The step from the investigation of in vitro interactions to an understanding of in vivo effects of 1,25-(OH)2D3 on immune cells requires further study. On the basis of information at hand, such as the potential for macrophage conversion of 25-OH-D3 to 1,25-(OH)2D3, decreased or increased macrophage function in association with vitamin D3 status in vitro and in vivo, as well as altered T cell subset ratios and proliferative responses with administration of the hormone, it is tempting to speculate that 1,25-(OH)2D3 exerts an influence on immune cell function in concert with other recognized soluble mediators of monocyte and lymphocyte origin. The primary influence of 1,25-(OH)2D3 may vary with the tissue site. Systemic levels of hormone may aid in maintaining tonic immunosuppression and thus prevent trivial antigenic stimuli from initiating an immune response. Upon initiation of an immune response to a significant antigenic challenge 1,25-(OH)2D3 may, in concert with other suppressor mechanisms, limit the extent of the host response by inhibition of IL 2 and IFN-gamma production. At local sites of chronic inflammation concentrations of 1,25-(OH)2D3 may be elevated and may act in an autocrine or paracrine fashion to alter the immune response, for example, by increasing IL 1 production and antigen presentation by tissue monocyte/macrophages. The activation of T cells is associated with the synthesis of 1,25-(OH)2D3 receptors, thus potentially limiting T cell proliferation in the presence of the hormone. Other biological actions of IL 1, however, including effects on cells in bone, joint, and brain may be augmented. Thus, the end result of the opposing effects of 1,25-(OH)2D3 on immune cells and their secretory products may vary with the specific cells involved, their state of maturation and activation, and the local concentrations of the hormone. Studies to date support the concept of an expanded role for 1,25-(OH)2D3 in immune cell biology.

Na,K-ATPase activity and 25(OH)vitamin D3 hydroxylation in rat proximal tubules.

The proximal tubule is the target site for parathyroid hormone (PTH), and conversion of 25(OH)vitamin D3 hormones which impinge on calcium (Ca) homeostasis, as well as a major site for sodium (Na) reabsorption. The effect of changes in PTH and vitamin D status on Na,K-ATPase activity, as a measure of Na transport, were studied in the proximal tubules of adult rat kidneys where Na and Ca reabsorption rates are in parallel. Na,K-ATPase activity and 25(OH)D3 metabolism were determined in cortical and juxtamedullary proximal tubule segments from normal, parathyroidectomized (PTX), and vitamin D-deficient (-D) rats. Na,K-ATPase activity was highest in cortical segments. PTX led to a decrease in activity in convoluted segments but increased activity in straight segments. In -D rats, Na,K-ATPase activity decreased in cortical segments but increased in juxtamedullary segments. 25(OH)D3 was metabolized more to 24,25(OH)2D3 than to 1,25(OH)2D3 in all normal segments. Juxtamedullary segments were more sensitive to PTX and -D conditions. These findings suggest that cortical and juxtamedullary nephrons are inherently different in basal Na,K-ATPase activity, in conversion of 25(OH)D3 to active metabolites, and in response to altered PTH and vitamin D3 status.

Studies on the relationship between vitamin D3 status and urinary excretion of calcium in healthy subjects: effects of increased levels of 25-hydroxyvitamin D3.

The metabolic consequences of a rapid increase in vitamin D status in healthy subjects were investigated. Circulating levels of 25-hydroxyvitamin D3 were increased by 224% in 12 healthy men by giving oral vitamin D3 for 7 weeks and by 200% in 15 healthy women by UVB irradiation for 7 weeks. No statistically significant effects on the serum levels of calcium, phosphate, creatinine, urate, albumin, PTH, basal urinary excretion of calcium, fasting urinary excretion of cAMP, or urinary excretion of calcium after calcium load tests were observed with the unpaired t-test. With the paired t-test the small stimulatory effects (about 25%) on basal urinary excretion of calcium became statistically significant in both experiments. The ratio between calcium and creatinine in fasting urine was significantly elevated following UVB irradiation (from 0.11 +/- 0.02 to 0.21 +/- 0.04, p less than 0.025 unpaired t-test, p less than 0.02 paired t-test) but not after oral intake of vitamin D3. The level of 1,25-dihydroxyvitamin D in serum was not affected to a statistically significant degree by oral vitamin D3, whereas there was a slight decrease from 48 +/- 3 to 39 +/- 3 pmol/l following UVB irradiation. It is concluded that an increase in the concentration of 25-hydroxyvitamin D3 up to about 125 nmol/l has small and negligible effects on calcium homeostasis in healthy subjects. This finding is discussed in relation to our previous finding that hypercalciuric renal stone formers have elevated serum levels of 25-hydroxyvitamin D3 as compared with normocalciuric stone formers and healthy subjects.

VITMAIN D3 RESPONSE IN SHEEP TO ORAL VERSUS PARENTERAL ADMINISTRATION AND TO INTRAMUSCULAR DOSE LEVELS OF VITAMIN D3

Plasma vitamin D3 concentration changes were assessed in 10 crossbred wethers following oral or intramuscular administration of a single massive dose (5 × 106 IU) of vitamin D3. Blood plasma was taken at different times during a 3-wk experimental period. The intramuscular response was higher than the oral. In another experiment 15 ewes were administered 5 × 106 IU of vitamin D3 orally, intramuscularly, or intravenously. Blood plasma was taken at different times during a 3-wk experimental period for analyses of plasma vitamin D3 and 25-hydroxyvitamin D3. All animals were killed at the end of the experiment and vitamin D3 determinations were carried out on various tissues. Vitamin D3 given to ewes parenterally had a greater and more lasting effect on their plasma concentrations of vitamin D3 and 25-hydroxyvitamin D3 than did oral administration. While plasma vitamin D3 concentrations of the two parenteral groups were approximately equal, the plasma 25-hydroxyvitamin D3 concentrations were substantially higher in the intravenously treated group than in the intramuscularly treated group. Tissue vitamin D3 concentrations in the parenteral group were higher than in the oral group, and the adipose tissue contained higher concentrations of vitamin D3 than did other tissues. In a third experiment crossbred wethers were administered intramuscularly various amounts (5 × 106, 5 × 105, and 5 × 104 IU) of vitamin D3 in a single dose. Blood plasma was taken at different times during the subsequent 2-wk period. There was proportionality between the amount of vitamin D3 injected and plasma vitamin D3 concentration. The results suggest that parenteral administration induces both higher tissue levels and higher circulating levels of vitamin D3 than does oral administration, and that intravenous injection produces higher circulating levels of 25-hydroxyvitamin D3 than does intramuscular injection. Key words: Vitamin D3 status, sheep, oral, parenteral

ENTEROHEPATIC CIRCULATION OF VITAMIN D: A REAPPRAISAL OF THE HYPOTHESIS

Vitamin-D metabolites in bile were investigated after oral and intravenous doses of radioactively labelled vitamin D had been given to six patients with T-tube biliary drainage after cholecystectomy. The vitamin was mainly excreted as highly polar inactivation products and less than 4% of the metabolites in bile were present as 25-hydroxyvitamin D or its glucuronide conjugate. There was insufficient vitamin D or 25-hydroxyvitamin D in bile for the reabsorption of these metabolites to make a significant contribution to normal vitamin-D status. Therefore interference with an enterohepatic circulation of vitamin-D metabolites cannot be a cause of vitamin-D deficiency.

Sunlight and vitamin D status in normal Saudi subjects

Serum levels of the circulating form of vitamin D3, 25-hydroxycholecalciferol [25-(OH)D3], were determined in 59 university students, 26 males and 33 females, aged 18 to 26 yr and in 24 elderly subjects, 13 males and 11 females, with a mean age of 62 ± 13 yr. The level of 25-(OH)D3 was significantly lower in the elderly persons (p < 0.001) than in young students of both sexes, and was significantly higher in females than in males. Serum levels of 1, 25- and 24, 25-dihydroxycholecalciferol were measured in adult males and found to be within the normal range. A group of elderly patients were exposed to natural uv light, and the circulating levels of 25-(OH)D3, serum phosphorus, and alkaline phosphatase were determined both before and 1 day after the last exposure. The exposure to natural uv light resulted in a 2½-fold increase in the level of 25-(OH)D3 and a significant decrease in the activity of alkaline phosphatase, but no significant change in serum phosphorus concentrations was observed. It is concluded that the low vitamin D3 status in Saudis is mainly due to avoidance of sunlight exposure and other factors discussed below.

Relation between hypercalciuria and vitamin D3-status in patients with urolithiasis.

Patients with urolithiasis were divided into two groups, one (n = 38) with a urinary excretion of calcium exceeding 6.0 mmol/24 h and one (n = 32) with a calcium excretion lower than 6.1 mmol/24 h. The group of patients with a high urinary excretion of calcium had a significantly higher level of 25-hydroxy vitamin D3 (26.2 +/- 1.6 ng/ml) than had the group of patients with a normal urinary excretion of calcium (17.6 +/- 0.9 ng/ml) (p less than 0.001). A highly specific and accurate method, based on isotope dilution--mass spectrometry was used in the assay of 25-hydroxy vitamin D3. There was no over-all correlation between level of 25-hydroxy vitamin D3 and serum level of calcium (r = 0.1). The results are in accordance with the contention that the vitamin D3-status might be of some importance for the development of hypercalciuria in these patients.

The Use of Bone Mineral Mass as an Indicator of Vitamin D Status in Turkeys ,

The interrelationships of several parameters as indicators of vitamin D3 in turkeys were determined. Poults were fed a rachitogenic diet supplemented with 0, 300, 600, 900, or 1200 ICU vitamin D3 per kilogram diet to 4 weeks of age. Relative bone mineral mass determined by 125I photon absorptiometry, as well as percent ash, breaking strength, and weight of dried, defatted tibiae were elevated by increasing amounts of dietary vitamin D3. The simple correlation coefficients for relative bone mineral mass, percent ash, and breaking strength vs. log (dietary vitamin D3 [ICU/kg] + 10) were .97, .93, and .94, respectively, when data from all treatments were used, and were .80, .78, and .14, respectively, when data from the basal treatment were eliminated. Correlation coefficients for relative bone mineral mass vs. bone weight, percent ash, breaking strength, and calcium binding activity were .86, .92, .93, and .96, respectively, when data from all treatments were used. The results indicate that bone mineral mass measured by photon absorptiometry is a good indicator of vitamin D3 status in the young poult.

SERUM-25-HYDROXYVITAMIN-D CONCENTRATIONS IN ADOLESCENT BOYS

In March, 1976, vitamin-D status was investigated in 256 thirteen-year-old school boys of Asian, West Indian, and European origin in Birmingham. Serum-25-hydroxyvitamin-D 3 (25-OHD 3) concentrations in 78% of the 124 Asian boys resembled those found in rickets and osteomalacia. Serum-25-OHD 3 concentrations were also low in a few West Indian and European children. Dietary intake of vitamin D and exposure to sunlight were similar in each group. Serum-parathormone concentrations were increased in many children with low serum-25-OHD 3. Reinvestigation in October, 1976, of a group of children whose serum-25-OHD, concentration had been less than 8 μg/l in March, 1976, showed pronounced improvement in all, but some still had concentrations which indicated a possible deficiency. It is suggested that the high frequency of vitamin-D deficiency in Asian adolescents would be much reduced if 1 mg of vitamin D3 was given orally each school term during adolesence.

A possible relationship between high-extraction cereal and rickets and osteomalacia.

The evidence of the present study suggests a strong and possibly causal relationship between high-extraction cereal and rickets and osteomalacia. It seems likely that this occurs when vitamin-D status is border-line. The rachitogenic component of high-extraction cereal remains to be identified; dietary phytate now seems unlikely and phytate-derived polyphosphate esters or dietary phosphorus may be incriminated. The present study strongly indicates that Mellanby's original suggestion of an "anti-calcifying substance" in high-extraction cereal remains valid.

Vitamin D 3-25-hydroxylase: Tissue occurrence and apparent lack of regulation

Vitamin D 3 -25-hydroxylase is the initial enzyme which participates in the pathway of conversion of vitamin D 3 to its hormonal form, 1,25-dihydroxy-vitamin D 3 . This enzyme was discovered by Horsting and DeLuca ( Biochem. Biophys. Res. Commun. 36 , 251–256 (1969)) and has been reported to occur only in liver and to be controlled via feedback inhibition by the product sterol. Our studies, measuring the conversion of vitamin D 3 to 25-hydroxy-vitamin D 3 by chick tissue homogenates, indicate that significant amounts of enzyme exist in kidney and intestine as well as liver. Since the kidney is the unique site of the 25-hydroxy-vitamin D 3 -1-hydroxylase enzyme, renal homogenates are capable of complete conversion of vitamin D 3 to its 1,25-dihydroxylated form. Further investigation of the vitamin D 3 -25-hydroxylase of chick liver homogenates demonstrates that it catalyzes 25-hydroxylation at a slow rate and is not strongly inhibited in the presence of excess product. The enzyme also appears to be unaffected by the vitamin D-status of the chick. Complementary experiments showing the strict control of the 25-hydroxy-vitamin D 3 -1-hydroxylase enzyme by the vitamin D and calcium status of chicks suggest that the regulation of production of the hormonal form of vitamin D resides almost totally at the level of the kidney 25-hydroxy-vitamin D 3 -1-hydroxylase.