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 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Vitamin D is absolutely essential for the maintenance of a healthy skeleton. Without vitamin D, children develop rickets and adults exacerbate their osteoporosis and develop osteomalacia. Casual exposure to sunlight is the major source of vitamin D for most people. During exposure to sunlight, ultraviolet B photons photolyze cutaneous stores of 7-dehydrocholesterol to previtamin D3. Previtamin D3 undergoes a thermal isomerization to form vitamin D3. Increased skin pigmentation, changes in latitude, time of day, sunscreen use, and aging can have a marked influence on the cutaneous production of vitamin D3. Once vitamin D3 is formed in the skin or ingested in the diet, it must be hydroxylated in the liver and kidney to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. It is now recognized that a wide variety of tissues and cells, both related to calcium metabolism and unrelated to calcium metabolism, are target sites for 1,25(OH)2D3. 1,25(OH)2D3 stimulates intestinal calcium absorption and mobilizes stem cells to mobilize calcium stores from bone. Noncalcemic tissues that possess receptors for 1,25(OH)2D3 respond to the hormone in a variety of ways. Of great interest is that 1,25(OH)2D3 is a potent antiproliferative and prodifferentiation mediator. As a result, 1,25(OH)2D3 and its analogs have wide clinical application in such diverse clinical disorders as rheumatoid and psoriatic arthritis; diabetes mellitus type I; hypertension; cardiac arrhythmias; seizure disorders; cancers of the breast, prostate, and colon; some leukemias and myeloproliferative disorders; chemotherapy-induced hair loss; and skin rejuvenation as well as skin diseases like psoriasis and ichthyosis.
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PMID:Noncalcemic actions of 1,25-dihydroxyvitamin D3 and clinical applications. 857 91

Studies in rats with renal ablation indicate that anemia lessens, whereas its vigorous correction with recombinant human erythropoietin (r-HuEPO) worsens systemic and glomerular hypertension, factors known to promote progression of chronic renal failure (CRF). However, in human studies, use of r-HuEPO in predialysis patients has not been associated with worsening renal function, provided blood pressure control is achieved. Histological evidence of bone disease is common in early renal failure, and deficits in calcitriol synthesis seem to be an important factor in the pathogenesis of secondary hyperparathyroidism (HPTH) in early CRF. Reports to data, on the use of low dose active vitamin D metabolites in predialysis patients, indicate either a reversible decline or no decline in renal function. Adynamic bone disease, however, may ensure during such therapy if excessive reductions in serum intact parathyroid hormone concentrations occur. Recent data suggest that chronic metabolic acidosis decreases albumin synthesis, increases muscle proteolysis, and induces negative nitrogen balance in patients with CRF. Despite these experimental data, the clinical relevance of correction of metabolic acidosis in end-stage renal disease (ESRD) is still not defined. Even though therapy of metabolic acidosis in the adult patient with CRF remains conjectural at this time, reports indicate that its correction might lead to healing of osteomalacia and osteopenia, and possibly may decrease protein degradation and improve growth in children with CRF.
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PMID:Use of erythropoietin, active vitamin D3 metabolites, and alkali agents in predialysis patients. 924 13

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.
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PMID:Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. 1172 70

Vitamin D is one of the oldest hormones that have been made in the earliest life forms for over 750 million years. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make vitamin D. Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of vitamin D is to maintain calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb dietary calcium. When there is inadequate calcium in the diet to satisfy the body's calcium requirement, vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the calcium stored in the bone. Vitamin D is metabolized in the liver and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. 1,25(OH)(2)D receptors (VDR) are present not only in the intestine and bone, but in a wide variety of other tissues, including the brain, heart, stomach, pancreas, activated T and B lymphocytes, skin, gonads, etc. 1,25(OH)(2)D is one of the most potent substances to inhibit proliferation of both normal and hyperproliferative cells and induce them to mature. It is also recognized that a wide variety of tissues, including colon, prostate, breast, and skin have the enzymatic machinery to produce 1,25(OH)(2)D. 1,25(OH)(2)D and its analogs have been developed for treating the hyperproliferative disease psoriasis. Vitamin D deficiency is a major unrecognized health problem. Not only does it cause rickets in children, osteomalacia and osteoporosis in adults, but may have long lasting effects. Chronic vitamin D deficiency may have serious adverse consequences, including increased risk of hypertension, multiple sclerosis, cancers of the colon, prostate, breast, and ovary, and type 1 diabetes. There needs to be a better appreciation of the importance of vitamin D for overall health and well being.
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PMID:Vitamin D: A millenium perspective. 1252 May 30

It is remarkable that phytoplankton and zooplankton have been producing vitamin D for more than 500 million years. The role of vitamin D in lower non-vertebrate life forms is not well understood. However, it is critically important that most vertebrates obtain an adequate source of vitamin D, either from exposure to sunlight or from their diet, in order to develop and maintain a healthy mineralized skeleton. Vitamin D deficiency is an unrecognized epidemic in most adults who are not exposed to adequate sunlight. This can precipitate and exacerbate osteoporosis and cause the painful bone disease osteomalacia. Once vitamin D is absorbed from the diet or made in the skin by the action of sunlight, it is metabolized in the liver to 25-hydroxyvitamin D [25(OH)D] and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)2D]. 1,25(OH)2D interacts with its nuclear receptor (VDR) in the intestine and bone in order to maintain calcium homeostasis. The VDR is also present in a wide variety of other tissues. 1,25(OH)2D interacts with these receptors to have a multitude of important physiological effects. In addition, it is now recognized that many tissues, including colon, breast and prostate, have the enzymatic machinery to produce 1,25(OH)2D. The insights into the new biological functions of 1,25(OH)2D in regulating cell growth, modulating the immune system and modulating the renin-angiotensin system provides an explanation for why diminished sun exposure at higher latitudes is associated with increased risk of dying of many common cancers, developing type 1 diabetes and multiple sclerosis, and having a higher incidence of hypertension. Another calciotropic hormone that is also produced in the skin, parathyroid hormone-related peptide, is also a potent inhibitor of squamous cell proliferation. The use of agonists and antagonists for PTHrP has important clinical applications for the prevention and treatment of skin diseases and disorders of hair growth.
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PMID:Evolution and function of vitamin D. 1289 11

Vitamin D is taken for granted and is not appreciated for its importance in overall health and well-being. Vitamin D, known as the sunshine vitamin, is appreciated as being important for the prevention of rickets in children. It is now recognized that vitamin D is important for not only the growing skeleton, but for the maintenance of a healthy musculoskeletal system throughout life. Vitamin D deficiency in adults precipitates and exacerbates osteoporosis and causes the painful bone disease osteomalacia. The revelation that vitamin D is biologically inactive and requires sequential hydroxylations in the liver and kidney to form 1,25-dihydroxyvitamin D helps explain why patients with renal failure are often resistant to vitamin D and suffer from secondary hyperparathyroidism and renal osteodystrophy. In addition to its role in maintaining calcium and phosphorus homeostasis, vitamin D is now being recognized as important for maintaining maximum muscle strength and for the prevention of many chronic diseases, including type I diabetes, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and many common cancers. Vitamin D status is best determined by the measurement of circulating levels of 25-hydroxyvitamin D. Vigilance for maintaining a 25-hydroxyvitamin D level of at least 20 ng/ml and preferably 30-50 ng/ml has important benefits for both healthy children and adults, as well as children and adults suffering from chronic kidney disease.
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PMID:Vitamin D for health and in chronic kidney disease. 1607 48

Vitamin D deficiency is now recognized as an epidemic in the United States. The major source of vitamin D for both children and adults is from sensible sun exposure. In the absence of sun exposure 1000 IU of cholecalciferol is required daily for both children and adults. Vitamin D deficiency causes poor mineralization of the collagen matrix in young children's bones leading to growth retardation and bone deformities known as rickets. In adults, vitamin D deficiency induces secondary hyperparathyroidism, which causes a loss of matrix and minerals, thus increasing the risk of osteoporosis and fractures. In addition, the poor mineralization of newly laid down bone matrix in adult bone results in the painful bone disease of osteomalacia. Vitamin D deficiency causes muscle weakness, increasing the risk of falling and fractures. Vitamin D deficiency also has other serious consequences on overall health and well-being. There is mounting scientific evidence that implicates vitamin D deficiency with an increased risk of type I diabetes, multiple sclerosis, rheumatoid arthritis, hypertension, cardiovascular heart disease, and many common deadly cancers. Vigilance of one's vitamin D status by the yearly measurement of 25-hydroxyvitamin D should be part of an annual physical examination.
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PMID:The vitamin D epidemic and its health consequences. 1625 41

During the past decade, major advances have been made in vitamin D research that transcend the simple concept that vitamin D is Important for the prevention of rickets in children and has little physiologic relevance for adults. Inadequate vitamin D, in addition to causing rickets, prevents children from attaining their genetically programmed peak bone mass, contributes to and exacerbates osteoporosis in adults, and causes the often painful bone disease osteomalacia. Adequate vitamin D is also important for proper muscle functioning, and controversial evidence suggests it may help prevent type 1 diabetes mellitus, hypertension, and many common cancers. Vitamin D inadequacy has been reported in approximately 36% of otherwise healthy young adults and up to 57% of general medicine inpatients in the United States and in even higher percentages in Europe. Recent epidemiological data document the high prevalence of vitamin D inadequacy among elderly patients and especially among patients with osteoporosis. Factors such as low sunlight exposure, age-related decreases in cutaneous synthesis, and diets low in vitamin D contribute to the high prevalence of vitamin D inadequacy. Vitamin D production from cutaneous synthesis or intake from the few vitamin D-rich or enriched foods typically occurs only intermittently. Supplemental doses of vitamin D and sensible sun exposure could prevent deficiency in most of the general population. The purposes of this article are to examine the prevalence of vitamin D inadequacy and to review the potential implications for skeletal and extraskeletal health.
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PMID:High prevalence of vitamin D inadequacy and implications for health. 1652 31

Vitamin D3 is modified by vitamin D3 25-hydroxylase in the liver, and by 25-hydroxyvitamin D3 1alpha-hydroxylase (CYP27B1) in the kidney, to form the active metabolite 1alpha,25-dihydroxyvitamin D3. Several vitamin D receptor (VDR) activators, including paricalcitol and calcitriol, are currently available for the treatment of hyperparathyroidism secondary to chronic kidney disease (CKD). CKD patients encounter a much higher risk of cardiovascular disease than do members of the general public, and recent clinical observations have shown that VDR activator therapy provides survival benefit for CKD patients in the rank order of paricalcitol > calcitriol > no VDR activator therapy, independent of parathyroid hormone, phosphorus and calcium. One possible explanation for this observation is that VDR activators exert a positive impact on cardiovascular functions. Studies in animals with disrupted genes involved in the vitamin D signaling pathway have provided some interesting data. For example, in mice lacking VDR or CYP27B1, it was found that in addition to the expected phenotype (hypocalcemia, secondary hyperparathyroidism and osteomalacia), expression of renin or atrial natriuretic peptide was elevated. The mice also developed hypertension and cardiac hypertrophy. Gene expression profiling studies have revealed that VDR may play a role in regulating smooth-muscle-cell (SMC) proliferation, thrombosis, fibrinolysis and vessel relaxation. Paricalcitol and calcitriol are equally potent at suppressing plasminogen activator inhibitor-1 synthesis and inhibiting cellular proliferation in human coronary artery SMCs. The effect of VDR activators on the modulation of renin expression and vascular functions may be factors that contribute to reduced mortality and morbidity risk in VDR-activator-treated CKD patients. In this review, we discuss recent preclinical and clinical data regarding the role of VDR and its ligands in the cardiovascular system.
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PMID:Cardiovascular disease in chronic kidney failure: the role of VDR activators. 1655 80

It is well-established that prolonged and severe vitamin D deficiency leads to rickets in children and osteomalacia in adults. More marginal vitamin D deficiency is likely to be a significant contributing factor to osteoporosis risk. However, recent emerging data from studies of adults suggest that low vitamin D status (serum 25-hydroxyvitamin D levels <50 nmol/l) may be contributing to the development of various chronic diseases, including cardiovascular disease, hypertension, diabetes mellitus, some inflammatory and autoimmune diseases, and certain cancers. Adequacy of vitamin D status in children and adolescents has been the focus of a number of recent investigations, and these studies have shown a high prevalence of low vitamin D status during the winter (especially in adolescents), with lower prevalence during the summer. Therefore, consideration of potential corrective strategies to allow children and adolescents to maintain adequate vitamin D status throughout the year, even in the absence of adequate summer sun exposure, is warranted.
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PMID:Vitamin D in childhood and adolescence. 1740 48


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