Seasonal variation of vitamin D in patients on hemodialysis.

BACKGROUND: Seasonal and racial differences in serum 25-hydroxyvitamin D levels have been studied extensively in the general population but not in patients with end-stage renal disease (ESRD). METHODS: Serum 25-hydroxyvitamin D levels, the best available index of vitamin D nutrition, was measured at the end of summer (September) in 142 chronic hemodialysis patients and again at the end of winter (April) in 73 of these 142 patients, to determine the prevalence and risk factors for vitamin D deficiency. RESULTS: The prevalence of vitamin D depletion, as defined by serum 25-hydroxyvitamin D level of less than 20 ng/ml (50 nmol/l), was 54% at the end of summer and further increased to 86% by the end of winter (p < 0.0001 summer vs. winter). We observed that women and African-Americans had a greater prevalence of hypovitaminosis D (p < 0.0002 and p < 0.001 for both comparisons, respectively). Surprisingly, diabetic status, age, and the duration of esrd were not associated with a significant increase in risk of vitamin d depletion. CONCLUSION: Vitamin D depletion is present in about half of ESRD patients with marked seasonal variations. Patients with ESRD should have more frequent assessments of their vitamin D nutrition by serum 25-hydroxyvitamin D levels, and vitamin D supplementation should be routinely prescribed, which may prevent many of the complications related to vitamin D deficiency and secondary hyperparathyroidism.

Vitamin D3 and its metabolites have no role in calcium and phosphorus metabolism in Tilapia mossambica.

The physiological function of vitamin D in fishes still remains uncertain. Earlier we observed no relationship between vitamin D3 content of several freshwater fishes and their calcemic/phosphatemic status and bone mineral content. In the present study the effects of vitamin D3 and its metabolites, 25-hydroxy vitamin D3 (25-OH-D3) and 1,25-dihydroxy vitamin D3 [1,25-(OH)2D3], administration on serum calcium-phosphorus levels, intestinal calcium absorption, whole-body calcium-phosphorus uptake, and gill calcium binding protein (CaBP) activity in the freshwater fish, Tilapia mossambica (Tilapia) was examined. It was observed that vitamin D3 and its metabolites could alter neither serum calcium-phosphorus levels nor intestinal calcium absorption and gill CaBP activity in fish at various doses. Further, the whole-body uptake of labelled calcium and phosphorus was also unaffected by vitamin D3/1,25-(OH)2D3 at different levels and/or at various lengths of time. Thus these studies indicate that unlike in terrestrial vertebrates, vitamin D3 or its metabolites are not needed for calcium-phosphorus homeostasis in fish.

Vitamin D2 is not biologically active for Rora (Labeo rohita) as vitamin D3.

The present investigation was directed towards finding the relative biopotency of vitamin D3 and D2 in fish. The freshwater column feeder fish Labeo rohita (Rora) was used for the study. The feeding of Rora with graded levels of vitamin D2 (550, 1,100 and 1,650 i.u./kg diet) and vitamin D3 (1,100 and 1,650 i.u./kg diet) resulted in no behavioural or morphological changes in comparison with the group fed a vitamin D-deficient diet. Also, the growth rate, feed efficiency, mortality rate, carcass protein, total lipids, calcium and phosphorus were found to remain unaltered in the vitamin D-deficient fish and fish fed any form of the vitamin. Further, there is no difference in any of the above parameters between the different doses of vitamin D3 or vitamin D2. Thus, the results of this study indicate that both of the forms of vitamin D (D2 or D3) are not biologically active for Rora (Labeo rohita) as a representative of freshwater fish.

Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate.

OBJECTIVE: To perform a meta-analysis of data from available published trials comparing the bioavailability of calcium carbonate with that of calcium citrate. DATA SOURCES: The whole set was comprised of 15 studies involving 184 subjects who underwent measurement of calcium absorption from calcium carbonate and calcium citrate. Category A excluded four studies for lack of physiological relevance, use of a mixed preparation with low content of calcium carbonate, or wide variability in results. Category B was comprised of five studies (from Category A) involving 71 subjects who took calcium supplements on an empty stomach. Category C was comprised of six studies (from Category A) involving 65 subjects who took calcium preparations with meals. METHOD: The meta-analysis of calcium absorption data from calcium carbonate and calcium citrate, with calculation of effect size and 95% confidence intervals. RESULTS: Calcium absorption from calcium citrate was consistently significantly higher than that from calcium carbonate by 20.0% in the whole set, by 24.0% in Category A, by 27.2% on an empty stomach, and by 21.6% with meals. CONCLUSION: Calcium citrate is better absorbed than calcium carbonate by approximately 22% to 27%, either on an empty stomach or co-administered with meals.

Effects of different regimens of sodium fluoride treatment for osteoporosis on the structure, remodeling and mineralization of bone.

We compared initial and final bone histomorphometric findings in 66 osteoporotic patients treated with sodium fluoride (NaF) according to three regimens, and in 7 osteoporotic patients who did not receive NaF. Fourteen patients received continuous NaF 75 mg/day (high-dose) with calcium 1500 mg/day for a mean of 41 months. Twenty-six patients received continuous NaF 50 mg/day (low-dose) with calcium 2000 mg/day for a mean of 15 months, either with (10 patients) or without (16 patients) vitamin D. Twenty-six patients received cyclical low-dose NaF, alternating with vitamin D, for a mean of 15 months and a total treatment duration of 28 months, of whom 14 were and 12 were not on NaF at the time of the second biopsy. Disregarding differences between regimens, there were significant increases in total and mineralized bone volume and trabecular thickness and nonsignificant decreases in these measurements in the control group. Fluoride-induced bone formation was exclusively appositional with no evidence for the creation of new trabeculae. The effect of low-dose NaF on bone structure was the same when the same total dose was given continuously or intermittently, and when the patient was or was not taking vitamin D. The increases in total and mineralized bone volume but not trabecular thickness were greater with high-dose than with low-dose NaF. Low-dose NaF caused modest but significant increases in all osteoid indices, and modest but significant declines in adjusted apposition rate and osteoid maturation rate and no change in bone formation rate. With high-dose NaF, the increase in BV/TV was greater but all indices of osteoid accumulation were much higher and all indices of impaired osteoblast function and mineralization were much lower, and 12 of 14 patients had some form of osteomalacia. This occurred also in 3 of 30 patients treated with low-dose NaF who were not taking vitamin D; the mean increase in osteoid thickness was significantly greater in these patients than in 22 low-dose patients who were taking vitamin D. We conclude: (1) The inconsistent effect of NaF in increasing bone strength is partly due to failure to restore connectivity in patients with severe bone loss and partly due to substantial osteoid accumulation. (2) Even low-dose NaF causes impaired osteoblast function, but this is much greater with high-dose prolonged therapy. (3) There is an unexplained discrepancy between the increase in bone formation implied by increases in spinal bone mineral and the lack of increase in bone formation measured histomorphometrically. (4) Defective mineralization is more closely related to the total cumulative dose of NaF than to the duration of treatment, and with low-dose treatment may be preventable by vitamin D. (5) Future clinical trials should be carried out with smaller doses of NaF and before there has been substantial loss of horizontal trabeculae in the spine.

Vitamin D is not an essential nutrient for Rora (Labeo rohita) as a representative of freshwater fish.

This investigation was directed towards finding the need of vitamin D for fish. The freshwater column feeder fish Labeo rohita (Rora) was used for the study. Early fry stage fish were divided into four experimental groups of 350 each: two groups were kept in natural light, while the other two were maintained under total darkness. One each of the light and dark-grown groups was supplied dietary vitamin D3 [1,650 i.u/kg diet], whereas the other groups were fed a vitamin D-deficient diet for six months. The known vitamin D-related functions and growth parameters were studied in these four experimental groups of fish. The results showed that fish reared on vitamin D-deficient diet and in dark did not have even traces of liver vitamin D, indicating a state of vitamin D deficiency in these fish. No significant differences were observed in percent bone to body weight or dry matter of the vitamin D-deficient/supplemented groups of fish grown in light/dark. Further, it was also observed that there were no significant changes in bone and carcass ash or calcium and phosphorus content in response to vitamin D3 supplementation as compared to the groups which did not receive vitamin D3 (grown both in light and dark). Also, there was little change in several other parameters like carcass protein and lipid, mortality rates, hepatosomatic index, and feed efficiency between the vitamin D-deficient/supplemented groups of fish. Thus, these findings suggest that vitamin D may not be an essential nutrient for Rora (Labeo rohita) as a representative of freshwater fish.

Bone histomorphometry in hypogonadal and eugonadal men with spinal osteoporosis.

We present iliac bone histomorphometric data after in vivo double tetracycline labeling and related biochemical data from 14 nonalcoholic men referred for evaluation of symptomatic spinal osteoporosis. Six patients had previously undiagnosed hypogonadism, and 8 had normal gonadal function and no evident etiology for osteoporosis. Bone histomorphometry revealed no differences in structural measurements or resorption indices between the 2 groups. However, compared to reference values for normal postmenopausal women, osteoblast surface, mineralizing surface, and formation rate were normal or modestly increased in the hypogonadal men and significantly reduced in the idiopathic group. There were significant corresponding differences between the 2 groups in the fasting urinary hydroxyproline to creatinine ratio, an index of bone resorption, and serum total alkaline phosphatase, an index of bone formation. Plasma 25-hydroxyvitamin D levels did not differ between the 2 groups and were above 10 ng/mL in all patients. Plasma 1,25-dihydroxyvitamin D [1,25-(OH)2D] levels were normal in the hypogonadal group and significantly reduced in the idiopathic group, but did not correlate with any histological measurements. The formation indices fell substantially in 3 of 4 hypogonadal men after 7-14 months of therapy with testosterone and a calcium supplement. We conclude the following. In vitamin D-replete hypogonadal men with osteoporosis, 1,25-(OH)2D synthesis is normal, and bone remodeling is modestly increased and correctable by hormone replacement therapy, as in normal postmenopausal women. In middle-aged men with idiopathic osteoporosis, there is impairment of 1,25-(OH)2D synthesis and of the recruitment and activity of teams of osteoblasts, as in postmenopausal osteoporosis.