{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,28]],"date-time":"2026-07-28T03:21:25Z","timestamp":1785208885469,"version":"3.55.0"},"reference-count":105,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2021,5,21]],"date-time":"2021-05-21T00:00:00Z","timestamp":1621555200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Czech Ministry of Health","award":["MH CZ\u2014DRO [Institute of Endocrinology, 00023761]"],"award-info":[{"award-number":["MH CZ\u2014DRO [Institute of Endocrinology, 00023761]"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Vitamin D is a micronutrient with pleiotropic effects in humans. Due to sedentary lifestyles and increasing time spent indoors, a growing body of research is revealing that vitamin D deficiency is a global problem. Despite the routine measurement of vitamin D in clinical laboratories and many years of efforts, methods of vitamin D analysis have yet to be standardized and are burdened with significant difficulties. This review summarizes several key analytical and clinical challenges that accompany the current methods for measuring vitamin D. According to an external quality assessment, methods and laboratories still produce a high degree of variability. Structurally similar metabolites are a source of significant interference. Furthermore, there is still no consensus on the normal values of vitamin D in a healthy population. These and other problems discussed herein can be a source of inconsistency in the results of research studies.<\/jats:p>","DOI":"10.3390\/nu13061758","type":"journal-article","created":{"date-parts":[[2021,5,24]],"date-time":"2021-05-24T00:01:20Z","timestamp":1621814480000},"page":"1758","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":40,"title":["Vitamin D: Current Challenges between the Laboratory and Clinical Practice"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0541-9620","authenticated-orcid":false,"given":"Ludmila","family":"M\u00e1\u010dov\u00e1","sequence":"first","affiliation":[{"name":"Institute of Endocrinology, N\u00e1rodni 8, 11694 Prague, Czech Republic"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marie","family":"Bi\u010d\u00edkov\u00e1","sequence":"additional","affiliation":[{"name":"Institute of Endocrinology, N\u00e1rodni 8, 11694 Prague, Czech Republic"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"316","DOI":"10.1016\/j.jsbmb.2006.12.078","article-title":"Extra-renal 25-hydroxyvitamin D3-1alpha-hydroxylase in human health and disease","volume":"103","author":"Hewison","year":"2007","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"5542","DOI":"10.1210\/en.2006-0946","article-title":"Minireview: Vitamin D receptor: New assignments for an already busy receptor","volume":"147","author":"Norman","year":"2006","journal-title":"Endocrinology"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"896","DOI":"10.4239\/wjd.v6.i7.896","article-title":"Metabolic syndrome: A review of the role of vitamin D in mediating susceptibility and outcome","volume":"6","author":"Strange","year":"2015","journal-title":"World J. Diabetes"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"365","DOI":"10.1152\/physrev.00014.2015","article-title":"Vitamin D: Metabolism, molecular mechanism of action, and pleiotropic effects","volume":"96","author":"Christakos","year":"2016","journal-title":"Physiol. Rev."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"458","DOI":"10.1111\/nan.12020","article-title":"Review: The role of vitamin D in nervous system health and disease","volume":"39","author":"DeLuca","year":"2013","journal-title":"Neuropathol. Appl. Neurobiol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"317","DOI":"10.33549\/physiolres.933902","article-title":"Vitamin D in autistic children and healthy controls","volume":"68","author":"Bicikova","year":"2019","journal-title":"Physiol. Res."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Mohan, M., Cherian, J.J., and Sharma, A. (2020). Exploring links between vitamin D deficiency and COVID-19. PLoS Pathog., 16.","DOI":"10.1371\/journal.ppat.1008874"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Grant, W.B., Lahore, H., McDonnell, S.L., Baggerly, C.A., French, C.B., Aliano, J.L., and Bhattoa, H.P. (2020). Evidence that vitamin d supplementation could reduce risk of influenza and COVID-19 infections and deaths. Nutrients, 12.","DOI":"10.20944\/preprints202003.0235.v2"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"60","DOI":"10.1016\/j.jsbmb.2016.09.016","article-title":"Non-musculoskeletal benefits of vitamin D","volume":"175","author":"Wimalawansa","year":"2018","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1016\/j.jsbmb.2018.09.003","article-title":"The serum vitamin D metabolome: What we know and what is still to discover","volume":"186","author":"Tuckey","year":"2019","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"408","DOI":"10.1002\/cbf.3421","article-title":"The vitamin D metabolome: An update on analysis and function","volume":"37","author":"Jenkinson","year":"2019","journal-title":"Cell Biochem. Funct."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"105","DOI":"10.1016\/S0002-9440(10)64162-4","article-title":"The ontogeny of 25-hydroxyvitamin D(3) 1alpha-hydroxylase expression in human placenta and decidua","volume":"161","author":"Zehnder","year":"2002","journal-title":"Am. J. Pathol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"22","DOI":"10.1016\/j.jsbmb.2013.12.009","article-title":"Regulation of the extrarenal CYP27B1-hydroxylase","volume":"144","author":"Adams","year":"2014","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Al-Zohily, B., Al-Menhali, A., Gariballa, S., Haq, A., and Shah, I. (2020). Epimers of Vitamin D: A Review. Int. J. Mol. Sci., 21.","DOI":"10.3390\/ijms21020470"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"15897","DOI":"10.1074\/jbc.M311473200","article-title":"C-3 epimerization of vitamin D3 metabolites and further metabolism of C-3 epimers: 25-hydroxyvitamin D3 is metabolized to 3-epi-25-hydroxyvitamin D3 and subsequently metabolized through C-1alpha or C-24 hydroxylation","volume":"279","author":"Kamao","year":"2004","journal-title":"J. Biol. Chem."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"988","DOI":"10.1016\/j.clinbiochem.2017.07.001","article-title":"S-25-hydroxyvitamin D and C3-epimers in pregnancy and infancy: An Odense Child Cohort study","volume":"50","author":"Mydtskov","year":"2017","journal-title":"Clin. Biochem."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3055","DOI":"10.1210\/jc.2006-0710","article-title":"C-3 epimers can account for a significant proportion of total circulating 25-hydroxyvitamin D in infants, complicating accurate measurement and interpretation of vitamin D status","volume":"91","author":"Singh","year":"2006","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"13","DOI":"10.3109\/10408363.2015.1074157","article-title":"Controversy and consensus regarding vitamin D: Recent methodological changes and the risks and benefits of vitamin D supplementation","volume":"53","author":"Glendenning","year":"2016","journal-title":"Crit. Rev. Clin. Lab. Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.jsbmb.2018.10.008","article-title":"Serum and synovial fluid vitamin D metabolites and rheumatoid arthritis","volume":"187","author":"Li","year":"2019","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Molnar, F., Sigueiro, R., Sato, Y., Araujo, C., Schuster, I., Antony, P., Peluso, J., Muller, C., Mourino, A., and Moras, D. (2011). 1alpha,25(OH)2-3-epi-vitamin D3, a natural physiological metabolite of vitamin D3: Its synthesis, biological activity and crystal structure with its receptor. PLoS ONE, 6.","DOI":"10.1371\/journal.pone.0018124"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"341","DOI":"10.1016\/j.jsbmb.2017.02.004","article-title":"1\u03b2,25-Dihydroxyvitamin D(3): A new vitamin D metabolite in human serum","volume":"173","author":"Pauwels","year":"2017","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"126","DOI":"10.1016\/j.ab.2011.06.043","article-title":"Simultaneous measurement of plasma vitamin D(3) metabolites, including 4\u03b2,25-dihydroxyvitamin D(3), using liquid chromatography-tandem mass spectrometry","volume":"418","author":"Wang","year":"2011","journal-title":"Anal. Biochem."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1348","DOI":"10.1210\/jc.2013-1366","article-title":"Placental CYP27B1 and CYP24A1 expression in human placental tissue and their association with maternal and neonatal calcitropic hormones","volume":"99","author":"Li","year":"2014","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1016\/j.jsbmb.2017.09.008","article-title":"Differential expression of vitamin D-associated enzymes and receptors in brain cell subtypes","volume":"177","author":"Landel","year":"2018","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1016\/j.abb.2011.11.003","article-title":"25-Hydroxyvitamin D-24-hydroxylase (CYP24A1): Its important role in the degradation of vitamin D","volume":"523","author":"Jones","year":"2012","journal-title":"Arch. Biochem. Biophys."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"6158","DOI":"10.1046\/j.1432-1327.2000.01680.x","article-title":"Dual metabolic pathway of 25-hydroxyvitamin D3 catalyzed by human CYP24","volume":"267","author":"Sakaki","year":"2000","journal-title":"Eur. J. Biochem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"424","DOI":"10.1016\/0003-9861(84)90422-3","article-title":"24-Oxo and 26,23-lactone metabolites of 1,25-dihydroxyvitamin D3 have direct bone-resorbing activity","volume":"230","author":"Stern","year":"1984","journal-title":"Arch. Biochem. Biophys."},{"key":"ref_28","first-page":"419","article-title":"Human pharmacokinetics of orally administered (24 R)-hydroxycalcidiol","volume":"31","author":"Leeuwenkamp","year":"1993","journal-title":"Eur. J. Clin. Chem. Clin. Biochem."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"48","DOI":"10.1016\/j.mce.2011.05.018","article-title":"Vitamin D metabolism, cartilage and bone fracture repair","volume":"347","author":"Naja","year":"2011","journal-title":"Mol. Cell. Endocrinol."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1111\/cen.12396","article-title":"Increased CYP24A1 expression is associated with BRAF(V600E) mutation and advanced stages in papillary thyroid carcinoma","volume":"81","author":"Zou","year":"2014","journal-title":"Clin. Endocrinol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/j.mce.2017.04.026","article-title":"Function of the vitamin D endocrine system in mammary gland and breast cancer","volume":"453","author":"Welsh","year":"2017","journal-title":"Mol. Cell. Endocrinol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2540","DOI":"10.1158\/1055-9965.EPI-09-0228","article-title":"Vitamin D related genes, CYP24A1 and CYP27B1, and colon cancer risk","volume":"18","author":"Dong","year":"2009","journal-title":"Cancer Epidemiol. Biomark. Prev."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1380","DOI":"10.1002\/ijc.28143","article-title":"Increased copy-number and not DNA hypomethylation causes overexpression of the candidate proto-oncogene CYP24A1 in colorectal cancer","volume":"133","author":"Hummel","year":"2013","journal-title":"Int. J. Cancer"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"144","DOI":"10.1038\/75985","article-title":"Quantitative mapping of amplicon structure by array CGH identifies CYP24 as a candidate oncogene","volume":"25","author":"Albertson","year":"2000","journal-title":"Nat. Genet."},{"key":"ref_35","first-page":"657","article-title":"Roles of steroid sulfatase in brain and other tissues","volume":"57","author":"Hampl","year":"2008","journal-title":"Physiol. Res."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"367","DOI":"10.1124\/dmd.117.078428","article-title":"Polymorphic human sulfotransferase 2A1 mediates the formation of 25-Hydroxyvitamin D(3)-3-O-Sulfate, a major circulating vitamin D metabolite in humans","volume":"46","author":"Wong","year":"2018","journal-title":"Drug Metab. Dispos."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1016\/0014-5793(85)80002-8","article-title":"25-Hydroxyvitamin D3 3-sulphate is a major circulating form of vitamin D in man","volume":"191","author":"Axelson","year":"1985","journal-title":"FEBS Lett."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"80","DOI":"10.1016\/j.jchromb.2015.12.014","article-title":"Determination of four sulfated vitamin D compounds in human biological fluids by liquid chromatography-tandem mass spectrometry","volume":"1009\u20131010","author":"Gomes","year":"2016","journal-title":"J. Chromatogr. B"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"851","DOI":"10.3855\/jidc.6600","article-title":"Serum 25-hydroxyvitamin D status in pregnant women with chronic hepatitis B virus infection","volume":"10","author":"Gao","year":"2016","journal-title":"J. Infect. Dev. Ctries."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"108812","DOI":"10.1016\/j.steroids.2021.108812","article-title":"Development of a LC-MS\/MS method to measure serum 3-sulfate and 3-glucuronide 25-hydroxyvitamin D3 metabolites; comparisons to unconjugated 25OHD in pregnancy and polycystic ovary syndrome","volume":"169","author":"Huynh","year":"2021","journal-title":"Steroids"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"6647","DOI":"10.1007\/s00216-014-8095-y","article-title":"Analysis of urinary vitamin D\u2083 metabolites by liquid chromatography\/tandem mass spectrometry with ESI-enhancing and stable isotope-coded derivatization","volume":"406","author":"Ogawa","year":"2014","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"969","DOI":"10.1210\/jcem-61-5-969","article-title":"Serum protein binding of 1,25-dihydroxyvitamin D: A reevaluation by direct measurement of free metabolite levels","volume":"61","author":"Bikle","year":"1985","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"748","DOI":"10.1172\/JCI112636","article-title":"Free 25-hydroxyvitamin D levels are normal in subjects with liver disease and reduced total 25-hydroxyvitamin D levels","volume":"78","author":"Bikle","year":"1986","journal-title":"J. Clin. Investig."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"901","DOI":"10.1016\/j.ecl.2017.07.013","article-title":"Current controversies: Are free vitamin metabolite levels a more accurate assessment of vitamin D status than total levels?","volume":"46","author":"Bikle","year":"2017","journal-title":"Endocrinol. Metab. Clin. N. Am."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.jsbmb.2017.11.014","article-title":"Why should we measure free 25(OH) vitamin D?","volume":"180","author":"Tsuprykov","year":"2018","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"34","DOI":"10.3343\/alm.2017.37.1.34","article-title":"Clinical utility of measurement of vitamin D-binding protein and calculation of bioavailable vitamin D in assessment of vitamin D status","volume":"37","author":"Kim","year":"2017","journal-title":"Ann. Lab. Med."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"84","DOI":"10.1038\/ki.2012.19","article-title":"Bioavailable vitamin D is more tightly linked to mineral metabolism than total vitamin D in incident hemodialysis patients","volume":"82","author":"Bhan","year":"2012","journal-title":"Kidney Int."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"60","DOI":"10.1093\/nutrit\/nux034","article-title":"Intestinal absorption of vitamin D: A systematic review","volume":"76","author":"Silva","year":"2018","journal-title":"Nutr. Rev."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1193","DOI":"10.1080\/10408398.2012.688897","article-title":"Vitamin D bioavailability: State of the art","volume":"55","author":"Borel","year":"2015","journal-title":"Crit. Rev. Food Sci. Nutr."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"808","DOI":"10.1210\/jc.2013-2872","article-title":"Exploring the role of vitamin D in type 1 diabetes, rheumatoid arthritis, and Alzheimer disease: New insights from accurate analysis of 10 forms","volume":"99","author":"Shah","year":"2014","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"72","DOI":"10.1016\/j.jsbmb.2011.05.003","article-title":"The ratio of serum 24,25-dihydroxyvitamin D(3) to 25-hydroxyvitamin D(3) is predictive of 25-hydroxyvitamin D(3) response to vitamin D(3) supplementation","volume":"126","author":"Wagner","year":"2011","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1016\/j.jchromb.2013.05.029","article-title":"Quantification of vitamin D and 25-hydroxyvitamin D in soft tissues by liquid chromatography-tandem mass spectrometry","volume":"932","author":"Lipkie","year":"2013","journal-title":"J. Chromatogr. B"},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"nzz074","DOI":"10.1093\/cdn\/nzz074","article-title":"Determination of vitamin D and its metabolites in human brain using an ultra-pressure lc-tandem mass spectra method","volume":"3","author":"Fu","year":"2019","journal-title":"Curr. Dev. Nutr."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"162","DOI":"10.1016\/j.jsbmb.2016.12.006","article-title":"Vitamin D metabolite concentrations in umbilical cord blood serum and associations with clinical characteristics in a large prospective mother-infant cohort in Ireland","volume":"167","author":"Kiely","year":"2017","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_55","doi-asserted-by":"crossref","unstructured":"Wierzejska, R., Jarosz, M., Sawicki, W., Bachanek, M., and Siuba-Strzeli\u0144ska, M. (2017). Vitamin D concentration in maternal and umbilical cord blood by season. Int. J. Environ. Res. Public Health, 14.","DOI":"10.3390\/ijerph14101121"},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"128","DOI":"10.2152\/jmi.66.128","article-title":"Seasonal variation of serum 25(OH) vitamin D levels in maternal and umbilical cord blood in Japanese women","volume":"66","author":"Sogawa","year":"2019","journal-title":"J. Med. Investig."},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"1058","DOI":"10.1194\/jlr.D092197","article-title":"Acylation derivatization based LC-MS analysis of 25-hydroxyvitamin D from finger-prick blood","volume":"60","author":"Le","year":"2019","journal-title":"J. Lipid Res."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"282","DOI":"10.1515\/jpme.1987.15.3.282","article-title":"Vitamin D3 metabolites in amniotic fluid in relation with maternal and fetal sera in term pregnancies","volume":"15","author":"Ron","year":"1987","journal-title":"J. Perinat. Med."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"1783","DOI":"10.1194\/jlr.D087569","article-title":"New LC-MS\/MS method with single-step pretreatment analyzes fat-soluble vitamins in plasma and amniotic fluid","volume":"59","author":"Le","year":"2018","journal-title":"J. Lipid Res."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"1086","DOI":"10.1007\/BF01711378","article-title":"25-Hydroxyvitamin D, 24, 25-dihydroxyvitamin D and 1,25-dihydroxyvitamin D in human cerebrospinal fluid","volume":"62","author":"Balabanova","year":"1984","journal-title":"Klin. Wochenschr."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"2567","DOI":"10.1210\/jc.2013-4388","article-title":"Clinical utility of simultaneous quantitation of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D by LC-MS\/MS involving derivatization with DMEQ-TAD","volume":"99","author":"Kaufmann","year":"2014","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"146","DOI":"10.1016\/j.jsbmb.2018.11.012","article-title":"Rapid liquid chromatography-tandem mass spectrometry method for determination of 24,25(OH)(2)D and 25OHD with efficient separation of 3-epi analogs","volume":"187","author":"Yu","year":"2019","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_63","doi-asserted-by":"crossref","first-page":"190","DOI":"10.1016\/j.clinbiochem.2012.10.037","article-title":"Analytical measurement and clinical relevance of vitamin D(3) C3-epimer","volume":"46","author":"Bailey","year":"2013","journal-title":"Clin. Biochem."},{"key":"ref_64","doi-asserted-by":"crossref","first-page":"1349","DOI":"10.1016\/0022-4731(83)90162-0","article-title":"An evaluation of the use of Sep-Pak C18 cartridges for the extraction of vitamin D3 and some of its metabolites from plasma and urine","volume":"19","author":"Rhodes","year":"1983","journal-title":"J. Steroid Biochem."},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1016\/S0378-4347(01)00047-0","article-title":"Rapid and sensitive high-performance liquid chromatographic method for simultaneous determination of retinol, alpha-tocopherol, 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in human plasma with photodiode-array ultraviolet detection","volume":"755","author":"Alvarez","year":"2001","journal-title":"J. Chromatogr. B"},{"key":"ref_66","doi-asserted-by":"crossref","first-page":"864","DOI":"10.1016\/j.clinbiochem.2011.04.020","article-title":"Comparison of high performance liquid chromatography, radio immunoassay and electrochemiluminescence immunoassay for quantification of serum 25 hydroxy vitamin D","volume":"44","author":"Jafri","year":"2011","journal-title":"Clin. Biochem."},{"key":"ref_67","doi-asserted-by":"crossref","first-page":"1835","DOI":"10.1016\/j.chroma.2011.02.004","article-title":"Vitamin D analysis in plasma by high performance liquid chromatography (HPLC) with C(30) reversed phase column and UV detection\u2014easy and acetonitrile-free","volume":"1218","author":"Jensen","year":"2011","journal-title":"J. Chromatogr. A"},{"key":"ref_68","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1373\/clinchem.2010.152553","article-title":"Candidate reference measurement procedures for serum 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 by using isotope-dilution liquid chromatography-tandem mass spectrometry","volume":"57","author":"Stepman","year":"2011","journal-title":"Clin. Chem."},{"key":"ref_69","doi-asserted-by":"crossref","first-page":"1942","DOI":"10.1021\/ac9026862","article-title":"Development of a candidate reference measurement procedure for the determination of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in human serum using isotope-dilution liquid chromatography-tandem mass spectrometry","volume":"82","author":"Tai","year":"2010","journal-title":"Anal. Chem."},{"key":"ref_70","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.chroma.2013.05.027","article-title":"Simultaneous analysis of circulating 25-hydroxy-vitamin D3, 25-hydroxy-vitamin D2, retinol, tocopherols, carotenoids, and oxidized and reduced coenzyme Q10 by high performance liquid chromatography with photo diode-array detection using C18 and C30 columns alone or in combination","volume":"1301","author":"Franke","year":"2013","journal-title":"J. Chromatogr. A"},{"key":"ref_71","doi-asserted-by":"crossref","first-page":"1264","DOI":"10.1016\/j.clinbiochem.2012.11.030","article-title":"Analytical measurement of serum 25-OH-vitamin D\u2083, 25-OH-vitamin D\u2082 and their C3-epimers by LC-MS\/MS in infant and pediatric specimens","volume":"46","author":"Yazdanpanah","year":"2013","journal-title":"Clin. Biochem."},{"key":"ref_72","doi-asserted-by":"crossref","first-page":"275","DOI":"10.1002\/jms.3522","article-title":"A simple micro-extraction plate assay for automated LC-MS\/MS analysis of human serum 25-hydroxyvitamin D levels","volume":"50","author":"Geib","year":"2015","journal-title":"J. Mass Spectrom."},{"key":"ref_73","doi-asserted-by":"crossref","first-page":"299","DOI":"10.1039\/C8AN01422A","article-title":"Development of a method for multiple vitamin D metabolite measurements by liquid chromatography coupled with tandem mass spectrometry in dried blood spots","volume":"144","author":"Rola","year":"2018","journal-title":"Analyst"},{"key":"ref_74","doi-asserted-by":"crossref","first-page":"3152","DOI":"10.1210\/jc.2003-031979","article-title":"Assay variation confounds the diagnosis of hypovitaminosis D: A call for standardization","volume":"89","author":"Binkley","year":"2004","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_75","doi-asserted-by":"crossref","first-page":"200","DOI":"10.1021\/ac60323a045","article-title":"Simple separation of vitamins D from sterols and retinol by argentation thin-layer chromatography","volume":"45","author":"Sklan","year":"1973","journal-title":"Anal. Chem."},{"key":"ref_76","doi-asserted-by":"crossref","first-page":"298","DOI":"10.1016\/0003-2697(77)90648-0","article-title":"Determination of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human plasma using high-pressure liquid chromatography","volume":"80","author":"Eisman","year":"1977","journal-title":"Anal. Biochem."},{"key":"ref_77","doi-asserted-by":"crossref","first-page":"1033","DOI":"10.1373\/clinchem.2015.241430","article-title":"Mass spectrometric profiling of vitamin D metabolites beyond 25-hydroxyvitamin D","volume":"61","author":"Volmer","year":"2015","journal-title":"Clin. Chem."},{"key":"ref_78","doi-asserted-by":"crossref","first-page":"110","DOI":"10.1016\/j.jsbmb.2015.09.026","article-title":"Vitamin D metabolite profiling using liquid chromatography-tandem mass spectrometry (LC-MS\/MS)","volume":"164","author":"Jones","year":"2016","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_79","doi-asserted-by":"crossref","first-page":"798","DOI":"10.1194\/jlr.D073536","article-title":"A new sensitive LC\/MS\/MS analysis of vitamin D metabolites using a click derivatization reagent, 2-nitrosopyridine","volume":"58","author":"Wan","year":"2017","journal-title":"J. Lipid Res."},{"key":"ref_80","doi-asserted-by":"crossref","first-page":"5615","DOI":"10.1007\/s00216-015-8733-z","article-title":"A candidate reference measurement procedure for quantifying serum concentrations of 25-hydroxyvitamin D\u2083 and 25-hydroxyvitamin D\u2082 using isotope-dilution liquid chromatography-tandem mass spectrometry","volume":"407","author":"Mineva","year":"2015","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_81","doi-asserted-by":"crossref","first-page":"7964","DOI":"10.1021\/acs.analchem.5b01861","article-title":"Candidate reference measurement procedure for the determination of (24R),25-Dihydroxyvitamin D3 in human serum using isotope-dilution liquid chromatography-tandem mass spectrometry","volume":"87","author":"Tai","year":"2015","journal-title":"Anal. Chem."},{"key":"ref_82","doi-asserted-by":"crossref","first-page":"1235","DOI":"10.3945\/ajcn.112.057182","article-title":"Evaluation of vitamin D Standardization Program protocols for standardizing serum 25-hydroxyvitamin D data: A case study of the program\u2019s potential for national nutrition and health surveys","volume":"97","author":"Cashman","year":"2013","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_83","doi-asserted-by":"crossref","first-page":"4420","DOI":"10.1002\/sim.6235","article-title":"The estimation of calibration equations for variables with heteroscedastic measurement errors","volume":"33","author":"Tian","year":"2014","journal-title":"Stat. Med."},{"key":"ref_84","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1016\/j.jsbmb.2016.12.002","article-title":"Vitamin D measurement standardization: The way out of the chaos","volume":"173","author":"Binkley","year":"2017","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_85","doi-asserted-by":"crossref","first-page":"1277","DOI":"10.5740\/jaoacint.17-0306","article-title":"Establishing an accuracy basis for the vitamin D External Quality Assessment Scheme (DEQAS)","volume":"100","author":"Burdette","year":"2017","journal-title":"J. AOAC Int."},{"key":"ref_86","doi-asserted-by":"crossref","first-page":"100","DOI":"10.1016\/j.jsbmb.2017.03.010","article-title":"Quality assessment of vitamin D metabolite assays used by clinical and research laboratories","volume":"173","author":"Carter","year":"2017","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_87","unstructured":"(2021, February 12). DEQAS. Available online: http:\/\/www.deqas.org."},{"key":"ref_88","unstructured":"(2021, February 12). NIST, Available online: https:\/\/www.nist.gov\/programs-projects\/vitamin-d-metabolites-quality-assurance-program."},{"key":"ref_89","unstructured":"(2021, March 21). SEKK. Available online: www.sekk.cz."},{"key":"ref_90","first-page":"508","article-title":"Vitamin D and immunomodulation: Is it time to change the reference values?","volume":"47","author":"Bivona","year":"2017","journal-title":"Ann. Clin. Lab. Sci."},{"key":"ref_91","doi-asserted-by":"crossref","first-page":"549","DOI":"10.1017\/S0007114509992017","article-title":"Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient\u2014A randomised, placebo-controlled trial","volume":"103","author":"Stonehouse","year":"2010","journal-title":"Br. J. Nutr."},{"key":"ref_92","doi-asserted-by":"crossref","first-page":"R195","DOI":"10.1530\/EC-20-0274","article-title":"Why do so many trials of vitamin D supplementation fail?","volume":"9","author":"Boucher","year":"2020","journal-title":"Endocr. Connect."},{"key":"ref_93","doi-asserted-by":"crossref","first-page":"17030","DOI":"10.1038\/boneres.2017.30","article-title":"New insights into the vitamin D requirements during pregnancy","volume":"5","author":"Hollis","year":"2017","journal-title":"Bone Res."},{"key":"ref_94","doi-asserted-by":"crossref","first-page":"582s","DOI":"10.1093\/ajcn\/88.2.582S","article-title":"Pharmacokinetics of vitamin D toxicity","volume":"88","author":"Jones","year":"2008","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_95","doi-asserted-by":"crossref","first-page":"373","DOI":"10.1210\/jcem-67-2-373","article-title":"Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin","volume":"67","author":"Webb","year":"1988","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_96","doi-asserted-by":"crossref","first-page":"860","DOI":"10.1093\/ajcn\/85.3.860","article-title":"Hypovitaminosis D in British adults at age 45 y: Nationwide cohort study of dietary and lifestyle predictors","volume":"85","author":"Power","year":"2007","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_97","unstructured":"Ross, A.C., Taylor, C.L., Yaktine, A.L., and Del Valle, H.B. (2011). Dietary Reference Intakes for Calcium and Vitamin D, National Academies Press (US). The National Academies Collection, Reports funded by National Institutes of Health."},{"key":"ref_98","doi-asserted-by":"crossref","first-page":"1911","DOI":"10.1210\/jc.2011-0385","article-title":"Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society clinical practice guideline","volume":"96","author":"Holick","year":"2011","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_99","doi-asserted-by":"crossref","first-page":"67","DOI":"10.1093\/ajcn\/65.1.67","article-title":"Plasma calcidiol, season, and serum parathyroid hormone concentrations in healthy elderly men and women","volume":"65","author":"Harris","year":"1997","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_100","doi-asserted-by":"crossref","first-page":"re4","DOI":"10.1126\/scisignal.275re4","article-title":"The vitamin D sterol-vitamin D receptor ensemble model offers unique insights into both genomic and rapid-response signaling","volume":"2","author":"Mizwicki","year":"2009","journal-title":"Sci. Signal."},{"key":"ref_101","doi-asserted-by":"crossref","first-page":"543","DOI":"10.1016\/j.beem.2011.05.010","article-title":"Vitamin D receptor (VDR)-mediated actions of 1\u03b1,25(OH)\u2082vitamin D\u2083: Genomic and non-genomic mechanisms","volume":"25","author":"Haussler","year":"2011","journal-title":"Best Pr. Res. Clin. Endocrinol. Metab."},{"key":"ref_102","first-page":"1518","article-title":"Comparison of 6-s-cis- and 6-s-trans-locked analogs of 1alpha,25-dihydroxyvitamin D3 indicates that the 6-s-cis conformation is preferred for rapid nongenomic biological responses and that neither 6-s-cis- nor 6-s-trans-locked analogs are preferred for genomic biological responses","volume":"11","author":"Norman","year":"1997","journal-title":"Mol. Endocrinol."},{"key":"ref_103","doi-asserted-by":"crossref","first-page":"190","DOI":"10.1016\/j.jsbmb.2012.08.008","article-title":"The pleiotropic effects of vitamin D in bone","volume":"136","author":"Anderson","year":"2013","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_104","doi-asserted-by":"crossref","first-page":"126","DOI":"10.1016\/j.jsbmb.2015.10.011","article-title":"Phenotypic, metabolic, and molecular genetic characterization of six patients with congenital adrenal hyperplasia caused by novel mutations in the CYP11B1 gene","volume":"155","author":"Nguyen","year":"2016","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_105","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1530\/EJE-18-0782","article-title":"Plasma steroid metabolome profiling for the diagnosis of adrenocortical carcinoma","volume":"180","author":"Schweitzer","year":"2019","journal-title":"Eur. J. Endocrinol."}],"container-title":["Nutrients"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-6643\/13\/6\/1758\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:05:34Z","timestamp":1760162734000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-6643\/13\/6\/1758"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,5,21]]},"references-count":105,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2021,6]]}},"alternative-id":["nu13061758"],"URL":"https:\/\/doi.org\/10.3390\/nu13061758","relation":{},"ISSN":["2072-6643"],"issn-type":[{"value":"2072-6643","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,5,21]]}}}