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Vitamin D

May 2007

Noncalcemic actions of vitamin D receptor ligands.

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

Endocr Rev. 2005 Aug;26(5):662-87

Wintertime vitamin D deficiency in male adolescents: effect on parathyroid function and response to vitamin D3 supplements.

The first part of this study consisted of an 18 month follow-up of the vitamin D status and parathyroid function in a group of 54 French male adolescents, aged from 13 to 16 years old and all pupils of a jockey training school. During the 18 month period four samplings were made, one every 6 months. The first was during September of the first year, the second and third during March and October of the second year, and the last in March of the third year. Therefore we had two main periods: summer and winter. The summer 25-hydroxyvitamin D (25(OH)D) concentrations were higher (71.6 +/- 19.9 and 52.4 +/- 16.5 nmol/l) than the winter ones (20.4 +/- 6.9 and 21.4 +/- 6.1 nmol/l). Conversely, the winter intact parathyroid hormone (iPTH) serum levels (4.18 +/- 1.18 and 4.11 +/- 1.35 pmol/l) were higher than the summer ones (2.44 +/- 0.82 and 2.71 +/- 0.71 pmol/l). At the two winter time points the 25(OH)D concentrations were lower than 25 nmol/l (10 ng/ml) in 72% (2nd year) and 68% (3rd year) of the adolescents. In the second part of the study we tried a vitamin D3 supplementation procedure designed to maintain the 25(OH)D and iPTH postsummer serum levels throughout the winter. Pairs of male adolescents matched for height, weight and Tanner pubertal stage were randomly assigned to either vitamin D3 supplementation (2.5 mg, i.e., 100,000 IU) administered orally at three specific periods (end of September, November and January) or no vitamin D3 treatment (control subjects). Blood was collected just before the first intake of vitamin D3 and 2 months after the last intake (March). The control subjects had blood drawn at the same time points. In the vitamin D3-treated subjects, the concentrations of 25 (OH)D (55.3 +/- 11.5 nmol/l) and of iPTH (3.09 +/- 1.16 pmol/l) in March and September (53.8 +/- 12.3 nmol/l and 2.75 +/- 1.26 pmol/l) were not significantly different. In the control subjects, March 25(OH)D levels (21.0 +/- nmol/l were low, with values below 25 nmol/l in 78% of subjects, and iPTH concentrations (3.97 +/- 1.08 pmol/l) were significantly (p<0.001) higher than in September (2.91 +/- 0.81 pmol/l). The constant vitamin D wintertime deficiency and wintertime rise in iPTH in adolescent French males throughout puberty has been demonstrated. In adolescents with low dairy calcium intakes, the vitamin D3 treatment was sufficient to maintain 25(OH)D concentrations at their summer levels throughout winter and to prevent an excessive wintertime rise in iPTH levels.

Osteoporos Int. 2001;12(10):875-9

The vitamin D epidemic and its health consequences.

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.

J Nutr. 2005 Nov;135(11):2739S-48S

Vitamin D intake and vitamin D status of Australians.

The main source of vitamin D for Australians is exposure to sunlight. Thus, levels of serum 25-hydroxyvitamin D(3), the indicator of vitamin D status, vary according to the season and are lower at the end of winter. In Australia and New Zealand, the prevalence of vitamin D deficiency varies, but is acknowledged to be much higher than previously thought. One study found marginal deficiency in 23% of women, and another frank deficiency in 80% of dark-skinned and veiled women. The groups at greatest risk of vitamin D deficiency in Australia are dark-skinned and veiled women (particularly in pregnancy), their infants, and older persons living in residential care. Only a few foods (eg, fish with a high fat content) contain significant amounts of vitamin D. In Australia, margarine and some milk and milk products are currently fortified with vitamin D. The average estimated dietary intake of vitamin D for men is 2.6-3.0 g/day and for women is 2.0-2.2 g/day. The estimated dietary requirement of vitamin D is at least 5.0 g/day and may be higher for older people. Adequate intake of vitamin D is unlikely to be achieved through dietary means, particularly in the groups at greatest risk, although vitamin D-fortified foods may assist in maintaining vitamin D status in the general population. An appropriate health message for vitamin D needs to balance the need for sunshine against the risk of skin cancer.

Med J Aust. 2002 Aug 5;177(3):149-52

Vitamin D status and its adequacy in healthy Danish perimenopausal women: relationships to dietary intake, sun exposure and serum parathyroid hormone.

We conducted this study to assess the prevalence of vitamin D insufficiency in a population of normal perimenopausal women, to examine the influence of sun exposure and vitamin D intake on the concentration of 25-hydroxyvitamin D (25OHD) and to examine the association between parathyroid hormone (PTH) and 25OHD. A total of 2016 healthy women aged 45-58, who had recently undergone a natural menopause, were enrolled over a 2.5-year period in the Danish Osteoporosis Prevention Study. A marked seasonal fluctuation of 25OHD was seen, with an abrupt rise in June and high values until October. The fluctuation could be related to number of hours of sunshine per month with a two months time lag. Dietary vitamin D intake, vitamin supplementation, sunlight exposure, and use of sun-bed were all significantly related to 25OHD concentrations. Sun exposure seemed to contribute the most. The overall prevalence of vitamin D deficiency (defined as serum ) was 7 %. However, in the subgroup avoiding direct sunshine and abstaining from vitamin D supplementation 32.8 % were vitamin D deficient in the winter-spring period. Although mean PTH was increased in the group with low serum 25OHD, PTH was not a sensitive marker of hypovitaminosis D in the individual, as only 16 % of those with vitamin D deficiency had PTH levels above normal range. Thus, we have shown, that healthy middle-aged Danish women are prone to vitamin D insufficiency in the winter-spring period, if they avoid sun exposure in the summer period and abstain from vitamin D supplementation.

Br J Nutr. 2001 Aug;86 Suppl 1:S97-103

Vitamin D compounds: clinical development as cancer therapy and prevention agents.

While 1,25 dihydroxycholecalciferol (calcitriol) is best recognized for its effects on bone and mineral metabolism, epidemiological data indicate that low vitamin D levels may play a role in the genesis and progression of breast, lung, colorectal and prostate cancer, as well as malignant lymphoma and melanoma. Calcitriol has strong antiproliferative effects in prostate, breast, colorectal, head/neck and lung cancer, as well as lymphoma, leukemia and myeloma model systems. Antiproliferative effects are seen in vitro and in vivo. The mechanisms of these effects are associated with G0/G1 arrest, induction of apoptosis, differentiation and modulation of growth factor-mediated signaling in tumor cells. In addition to the direct effects on tumor cells, recent data strongly support the hypothesis that the stromal effects of vitamin D analogs (e.g., direct effects on tumor vasculature) are also important in the antiproliferative effects. Antitumor effects are seen in a wide variety of tumor types and there are few data to suggest that vitamin D-based approaches are more effective in any one tumor type. Glucocorticoids potentiate the antitumor effect of calcitriol and decrease calcitriol-induced hypercalcemia. In addition, calcitriol potentiates the antitumor effects of many cytotoxic agents. Preclinical data indicate that maximal antitumor effects are seen with pharmacological doses of calcitriol and that such exposure can be safely achieved in animals using a high dose, intermittent schedule of administration. AUC and C(max) calcitriol concentrations of 32 ng.h/ml and 9.2 ng/ml are associated with striking antitumor effects in a murine squamous cell carcinoma model and there is increasing evidence from clinical trials that such exposures can be safely attained in patients. Another approach to maximizing intra-tumoral exposure to vitamin D analogs is to inhibit their catabolism. The data clearly indicate that agents which inhibit the major vitamin D catabolizing enzyme, CYP24 (24 hydroxylase), potentiate calcitriol killing of prostate tumor cells in vitro and in vivo. Phase I and II trials of calcitriol, either alone or in combination with carboplatin, taxanes or dexamethasone, as well as the non-specific CYP24 inhibitor, ketoconazole, have been initiated in patients with androgen-dependent and -independent prostate cancer and other advanced cancers. The data indicate that high-dose calcitriol is feasible on an intermittent schedule, no dose-limiting toxicity has been encountered, but the optimal dose and schedule remain to be delineated. Clinical responses have been seen with the combination of high-dose calcitriol + dexamethasone in androgen-independent prostate cancer (AIPC) and, in a large randomized trial in men with AIPC, potentiation of the antitumor effects of docetaxel were seen.

Anticancer Res. 2006 Jul-Aug;26(4A):2551-6

Vitamin D

The vitamin D endocrine system plays an essential role in calcium homeostasis and bone metabolism, but research during the past two decades has revealed a diverse range of biological actions that include induction of cell differentiation, inhibition of cell growth, immunomodulation, and control of other hormonal systems. Vitamin D itself is a prohormone that is metabolically converted to the active metabolite, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. This vitamin D hormone activates its cellular receptor (vitamin D receptor or VDR), which alters the transcription rates of target genes responsible for the biological responses. This review focuses on several recent developments that extend our understanding of the complexities of vitamin D metabolism and actions: the final step in the activation of vitamin D, conversion of 25-hydroxyvitamin D to 1,25(OH)(2)D in renal proximal tubules, is now known to involve facilitated uptake and intracellular delivery of the precursor to 1alpha-hydroxylase. Emerging evidence using mice lacking the VDR and/or 1alpha-hydroxylase indicates both 1,25(OH)(2)D(3)-dependent and -independent actions of the VDR as well as VDR-dependent and -independent actions of 1,25(OH)(2)D(3). Thus the vitamin D system may involve more than a single receptor and ligand. The presence of 1alpha-hydroxylase in many target cells indicates autocrine/paracrine functions for 1,25(OH)(2)D(3) in the control of cell proliferation and differentiation. This local production of 1,25(OH)(2)D(3) is dependent on circulating precursor levels, providing a potential explanation for the association of vitamin D deficiency with various cancers and autoimmune diseases.

Am J Physiol Renal Physiol. 2005 Jul;289(1):F8-28

Epidemiology of disease risks in relation to vitamin D insufficiency.

Vitamin D from ultraviolet-B (UVB) irradiance, food, and supplements is receiving increased attention lately for its role in maintaining optimal health. Although the calcemic effects of vitamin D have been known for about a century, the non-calcemic effects have been studied intently only during the past two-three decades. The strongest links to the beneficial roles of UVB and vitamin D to date are for bone and muscle conditions and diseases. There is also a preponderance of evidence from a variety of studies that vitamin D reduces the risk of colon cancer, with 1000 IU/day of vitamin D or serum 25-hydroxyvitamin D levels >33 ng/mL (82 nmol/L) associated with a 50% lower incidence of colorectal cancer. There is also reasonable evidence that vitamin D reduces the risk of breast, lung, ovarian, and prostate cancer and non-Hodgkin’s lymphoma. There is weaker, primarily ecologic, evidence for the role of vitamin D in reducing the risk of an additional dozen types of cancer. There is reasonably strong ecologic and case-control evidence that vitamin D reduces the risk of autoimmune diseases including such as multiple sclerosis and type 1 diabetes mellitus, and weaker evidence for rheumatoid arthritis, osteoarthritis, type 2 diabetes mellitus, hypertension and stroke. It is noted that mechanisms whereby vitamin D exerts its effect are generally well understood for the various conditions and diseases discussed here.

Prog Biophys Mol Biol. 2006 Sep;92(1):65-79

The role of vitamin D in left ventricular hypertrophy and cardiac function.

The role of vitamin D in left ventricular hypertrophy and cardiac function. Cardiovascular disease is the leading cause of death among patients with end-stage renal disease (ESRD). Traditional cardiac risk factors, as well as other factors specific to the ESRD population such as hyperphosphatemia, elevated calcium and phosphate product, abnormal lipid metabolism, hyperhomocysteinemia, and chronic inflammation play a role in the excessive risk of cardiovascular death in this population. Left ventricular disorders are proven risk factors for cardiac mortality in hemodialysis patients. These disorders are present in incident ESRD patients at rates far above the general population. There is an accumulating body of evidence that suggests that vitamin D plays a role in cardiovascular disease. Abnormal vitamin metabolism, through deficiency of the active form of 1,25-dihydroxyvitamin D(3), and acquired vitamin D resistance through the uremic state, have been shown to be important in ESRD. Vitamin D deficiency has long been known to affect cardiac contractility, vascular tone, cardiac collagen content, and cardiac tissue maturation. Recent studies using vitamin D receptor deficient mice as a model demonstrate a crucial role of vitamin D in regulation of the renin-angiotensin system. Additionally, there is emerging evidence linking treatment with vitamin D to improved survival on hemodialysis and improvement in cardiac function. The emergence of this data is focusing attention on the previously underappreciated nonmineral homeostatic effects of vitamin D that very likely play an important role in the pathogenesis of cardiac disease in ESRD.

Kidney Int Suppl. 2005 Jun;(95):S37-42

Vitamin D and its analogues: do they protect against cardiovascular disease in patients with kidney disease?

BACKGROUND: Patients with chronic kidney disease (CKD) are at high risk for cardiovascular disease, and despite recent advances in hypertension control, anemia management, and dialysis adequacy, mortality remains high. Improved understanding of nontraditional risk factors, including those present at early phases in CKD, may lead to novel therapeutic strategies. CKD has been demonstrated to be an independent risk factor for cardiovascular disease in the general population, but data are lacking as to the associated potential abnormalities that occur in association with reduced glomerular filtration rate (GFR), which may contribute to this increased risk. Data are accumulating regarding the role of abnormalities of calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) in cardiovascular disease. Vitamin D deficiency is present even in the early stages of CKD. Vitamin D plays a central role in calcium-phosphorus homeostasis, regulation of PTH, and formation and maintenance of bone. However, until recently, vitamin D has not been considered to have a biologic role in CKD beyond mineral regulation, or has been considered as a negative factor contributing to soft tissue and cardiovascular calcification. In light of recent observational studies showing an association of vitamin D therapy and survival benefit in hemodialysis patients, the effects of vitamin D on cardiovascular system have become a heavily debated issue. METHODS: A Medline search was performed to identify relevant literature describing the role of vitamin D in the pathogenesis of cardiovascular disease. Both the experimental and clinical literatures in English were reviewed. RESULTS: The accumulating published data demonstrate both associative relationships and mechanisms for biologic plausibility. The following three potential mechanisms may be important for the protective effects of vitamin D against cardiovascular disease mortality: vitamin D can inhibit various aspects of inflammation, which have been established as a key pathogenic mechanism in atherosclerosis; vitamin D exerts an antiproliferative effect on myocardial cell hypertrophy and proliferation, which underlies the pathogenesis of congestive heart failure; and vitamin D acts as a negative endocrine regulator for the renin-angiotensin system, which itself plays an important independent role in hypertension and cardiovascular health. CONCLUSION: Vitamin D deficiency might be an underestimated nonclassical risk factor for cardiovascular disease in CKD. Based on a review of the evidence, from both basic science and clinical studies, this article supports the possible protective role of vitamin D beyond its effect on mineral metabolism, and suggests the need for ongoing evaluation of the role of vitamin D in cardiovascular health in the CKD population.

Kidney Int. 2005 Nov;68(5):1973-81