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Vitamin D status: measurement, interpretation, and clinical application. Holick MF. Ann Epidemiol. 2009 Feb;19(2):73-8. Epub 2008 Mar 10. Review. PMID: 18329892 Conclusion The only way to determine whether a person is vitamin D deficient or sufficient is to measure their circulating level of 25(OH)D. There are a variety of assays used to measure 25(OH)D. The radioimmunoassays and competitive protein binding assays for 25(OH)D are useful in detecting vitamin D deficiency and sufficiency. However, these assays are fraught with technical difficulties, especially if they are not run routinely (Fig. 4) (33). Several reference laboratories have now switched to LC-MS ,which measures both 25(OH)D2 and 25(OH)D3 quantitatively. The total 25(OH)D, i.e., 25(OH)D2 plus 25(OH)D3, is what physicians need to be aware of for their patients. A level >30 ng/mL is

The vitamin D-antimicrobial peptide pathway and its role in protection against infection. Gombart AF. Future Microbiol. 2009 Nov;4:1151-65. PMID: 19895218 Vitamin D deficiency has been correlated with increased rates of infection. Since the early 19th century, both environmental (i.e., sunlight) and dietary sources (cod liver) of vitamin D have been identified as treatments for TB. The recent discovery that vitamin D induces antimicrobial peptide gene expression explains, in part, the 'antibiotic' effect of vitamin D and has greatly renewed interest in the ability of vitamin D to improve immune function. Subsequent work indicates that this regulation is biologically important for the response of the innate immune system to wounds and infection and that deficiency may lead to suboptimal responses toward bacterial and viral infections. The regulation of the cathelicidin antimicrobial peptide gene is a human/primate-specific adaptation and is not conserved in other mammals. The capacity of the vitamin D receptor to act as a high-affinity receptor for vitamin D and a low-affinity receptor for secondary bile acids and potentially other novel nutritional compounds suggests that the evolutionary selection to place the cathelicidin gene under control of the vitamin D receptor allows for its regulation under both endocrine and xenobiotic response systems. Future studies in both humans and humanized mouse models will elucidate the importance of this regulation and lead to the development of potential therapeutic applications