Vitamin D
Vitamin D is a steroid and is vitamin that "includes both cholecalciferols and ergocalciferols, which have the common effect of preventing or curing rickets in animals. It can also be viewed as a hormone since it can be formed in skin by action of ultraviolet rays upon the precursors, 7-dehydrocholesterol and ergosterol, and acts on vitamin D receptors to regulate calcium in opposition to parathyroid hormone."[1]
Vitamin D serves two classes of functions: (a) an endocrine function, in which a form of vitamin D, calcitriol, produced in the kidneys and secreted into the bloodstream, acts on target organs (gastrointestinal tract, bone, parathyroid glands) in such a way as to regulate aspects of calcium and phosphorus metabolism important to bone health and homeostasis of circulating calcium and phosphorus concentrations; and, (b) an autocrine function, in which the cells of numerous organs and tissues in the body (e.g., parts of the immune system, various epithelial tissues) generate calcitriol that functions in the cells that generate it, in intracellular signaling pathways (e.g., facilitation of the expression of specific genes) important to optimal functioning of those cells.[2] The autocrine mechanisms account for the preponderance of vitamin D utilized by body each day, and therefore tends to set the daily requirement for vitamin D.[2]
Biochemistry
Ergocalciferols (vitamin D2) is formed in plants. Ergocalciferols are "derivatives of ergosterol formed by ultraviolet rays breaking of the C9-C10 bond. They differ from cholecalciferol in having a double bond between C22 and C23 and a methyl group at C24."[3]
Cholecalciferol (vitamin D3) is formed in the skin of animals from 7-dehydrocholesterol by sunlight. Cholecalciferol is a "derivative of 7-dehydroxycholesterol formed by ultraviolet rays breaking of the C9-C10 bond. It differs from ergocalciferol in having a single bond between C22 and C23 and lacking a methyl group at C24."[4]
Vitamin D2 and vitamin D3 are of equal potency.[5]
Vitamin D2 and vitamin D3 are hydroxylated in the liver at the 25 position.[5] This leads to calcitriol (1,25-Dihydroxyvitamin D3). Calcitriol is the "physiologically active form of vitamin D. It is formed primarily in the kidney by enzymatic hydroxylation of 25-hydroxycholecalciferol (calcifediol). Its production is stimulated by low blood calcium levels and parathyroid hormone. Calcitriol increases intestinal absorption of calcium and phosphorus, and in concert with parathyroid hormone increases bone resorption."[6]
Deficiency
Low levels of vitamin D are common in medical inpatients[7] and some populations of patients with widespread musculoskeletal pain like fibromyalgia[8].[9] However, more recent studies make the associated between Vitamin D and non-specific pain doubtful.[10][10]
Administration
In health adults, Vitamin D2 and vitamin D3 are equally effective in maintaining serum 25-hydroxyvitamin D levels.[11]
References
- ↑ Anonymous (2024), Vitamin D (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ 2.0 2.1 Heaney RP. (2008) 10.2215/CJN.01160308 Vitamin D in Health and Disease. Clin. J. Am. Soc. Nephrol. (first published online June 4, 2008)
- ↑ Anonymous (2024), Ergocalciferols (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Anonymous (2024), Cholecalciferol (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ 5.0 5.1 Harper, Harold W.; Murray, Robert F. (2000). “Structure and Function of the Lipid-Soluble Vitamins”, Harper's Biochemistry. Norwalk, CT: Appleton & Lange, 645. ISBN 0-8385-3684-0.
- ↑ Anonymous (2024), Calcitriol (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Thomas MK, Lloyd-Jones DM, Thadhani RI, et al (1998). "Hypovitaminosis D in medical inpatients". N. Engl. J. Med. 338 (12): 777–83. PMID 9504937. [e]
- ↑ Plotnikoff GA, Quigley JM (2003). "Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific musculoskeletal pain". Mayo Clin. Proc. 78 (12): 1463–70. PMID 14661675. [e]
- ↑ Hicks GE, Shardell M, Miller RR, et al (May 2008). "Associations between vitamin D status and pain in older adults: the Invecchiare in Chianti study". J Am Geriatr Soc 56 (5): 785–91. DOI:10.1111/j.1532-5415.2008.01644.x. PMID 18331295. Research Blogging.
- ↑ 10.0 10.1 Warner AE, Arnspiger SA (February 2008). "Diffuse musculoskeletal pain is not associated with low vitamin D levels or improved by treatment with vitamin D". J Clin Rheumatol 14 (1): 12–6. DOI:10.1097/RHU.0b013e31816356a9. PMID 18431091. Research Blogging.
- ↑ Holick MF, Biancuzzo RM, Chen TC, et al (2008). "Vitamin D2 is as effective as vitamin D3 in maintaining circulating concentrations of 25-hydroxyvitamin D". J. Clin. Endocrinol. Metab. 93 (3): 677-81. DOI:10.1210/jc.2007-2308. PMID 18089691. Research Blogging.