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Measurement of vitamin D levels in inflammatory bowel disease patients reveals a subset of Crohn's disease patients with elevated 1,25-dihydroxyvitamin D and low bone mineral density. Abreu MT, Kantorovich V, Vasiliauskas EA, Gruntmanis U, Matuk R, Daigle K, Chen S, Zehnder D, Lin YC, Yang H, Hewison M, Adams JS. Gut. 2004 Aug;53(8):1129-36. PMID: 15247180 doi: 10.1136/gut.2003.036657. Conclusions: These data demonstrate that elevated 1,25(OH)2D is more common in CD than previously appreciated and is independently associated with low bone mineral density. The source of the active vitamin D may be the inflamed intestine. Treatment of the underlying inflammation may improve metabolic bone disease in this subgroup of patients.

[Low levels of 25-hydroxyvitamin D (25OHD) in patients with inflammatory bowel disease and its correlation with bone mineral density] Souza HN, Lora FL, Kulak CA, Mañas NC, Amarante HM, Borba VZ. Arq Bras Endocrinol Metabol. 2008 Jun;52(4):684-91. Portuguese. PMID: 18604382

Vitamin D in preventive medicine: are we ignoring the evidence? Zittermann A. Br J Nutr. 2003 May;89(5):552-72. Review. PMID: 12720576 Vitamin D is metabolised by a hepatic 25-hydroxylase into 25-hydroxyvitamin D (25(OH)D) and by a renal 1alpha-hydroxylase into the vitamin D hormone calcitriol. Calcitriol receptors are present in more than thirty different tissues. Apart from the kidney, several tissues also possess the enzyme 1alpha-hydroxylase, which is able to use circulating 25(OH)D as a substrate. Serum levels of 25(OH)D are the best indicator to assess vitamin D deficiency, insufficiency, hypovitaminosis, adequacy, and toxicity. European children and young adults often have circulating 25(OH)D levels in the insufficiency range during wintertime. Elderly subjects have mean 25(OH)D levels in the insufficiency range throughout the year. In institutionalized subjects 25(OH)D levels are often in the deficiency range. There is now general agreement that a low vitamin D status is involved in the pathogenesis of osteoporosis. Moreover, vitamin D insufficiency can lead to a disturbed muscle function. Epidemiological data also indicate a low vitamin D status in tuberculosis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases, hypertension, and specific types of cancer. Some intervention trials have demonstrated that supplementation with vitamin D or its metabolites is able: (i) to reduce blood pressure in hypertensive patients; (ii) to improve blood glucose levels in diabetics; (iii) to improve symptoms of rheumatoid arthritis and multiple sclerosis. The oral dose necessary to achieve adequate serum 25(OH)D levels is probably much higher than the current recommendations of 5-15 microg/d.

Vitamin D and calcium insufficiency-related chronic diseases: molecular and cellular pathophysiology. Peterlik M, Cross HS. Eur J Clin Nutr. 2009 Dec;63(12):1377-86. Epub 2009 Sep 2. PMID: 19724293 doi:10.1038/ejcn.2009.105 A compromised vitamin D status, characterized by low 25-hydroxyvitamin D (25-(OH)D) serum levels, and a nutritional calcium deficit are widely encountered in European and North American countries, independent of age or gender. Both conditions are linked to the pathogenesis of many degenerative, malignant, inflammatory and metabolic diseases. Studies on tissue-specific expression and activity of vitamin D metabolizing enzymes, 25-(OH)D-1alpha-hydroxylase and 25-(OH)D-24-hydroxylase, and of the extracellular calcium-sensing receptor (CaR) have led to the understanding of how, in non-renal tissues and cellular systems, locally produced 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and extracellular Ca2+ act jointly as key regulators of cellular proliferation, differentiation and function. Impairment of cooperative signalling from the 1,25-(OH)2D3-activated vitamin D receptor (VDR) and from the CaR in vitamin D and calcium insufficiency causes cellular dysfunction in many organs and biological systems, and, therefore, increases the risk of diseases, particularly of osteoporosis, colorectal and breast cancer, inflammatory bowel disease, insulin-dependent diabetes mellitus type I, metabolic syndrome, diabetes mellitus type II, hypertension and cardiovascular disease. Understanding the underlying molecular and cellular processes provides a rationale for advocating adequate intake of vitamin D and calcium in all populations, thereby preventing many chronic diseases worldwide.