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The beneficial effects of ultraviolet light B (UVB) phototherapy in psoriasis are partly attributed to UVB-induced increase of vitamin D levels. In clinical practice, total 25-hydroxy vitamin D (25(OH)D) levels are measured to assess sufficiency, but it might be more accurate to measure free 25(OH)D levels. The aim of this study was to measure free serum 25(OH)D levels in psoriasis patients before and after phototherapy and to investigate if free 25(OH)D correlates stronger to disease severity than total 25(OH)D. Twenty adults (&gt;18 years) with psoriasis were included for treatment with narrow-band UVB (NB-UVB) phototherapy for 10\u201312 weeks. Psoriasis Area and Severity Index (PASI) and Visual Analogue Scale (VAS) were used to assess disease severity. Serum levels of total 25(OH)D, free 25(OH)D, and 1,25(OH)2D were measured before and after NB-UVB. Total 25(OH)D, free 25(OH)D, 1,25(OH)2D and the percentage of free 25(OH)D increased after NB-UVB, and PASI and VAS improved. The increase in total and free 25(OH)D remained significant when stratifying for vitamin D confounders. No correlations between disease severity and vitamin D levels were found. Total and free 25(OH)D levels were positively correlated before and after NB-UVB. NB-UVB is an effective treatment for mild to severe plaque psoriasis and increases not only total but also free 25(OH)D levels, as well as the percentage of free 25(OH)D, suggesting an increased bioavailability of skin-produced vitamin D.<\/jats:p>","DOI":"10.3390\/biom13071018","type":"journal-article","created":{"date-parts":[[2023,6,21]],"date-time":"2023-06-21T02:01:33Z","timestamp":1687312893000},"page":"1018","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["The Effect of Narrow-Band Ultraviolet B Phototherapy on Free and Total Vitamin D Serum Levels in Mild to Severe Plaque Psoriasis"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6349-2757","authenticated-orcid":false,"given":"Andrea","family":"Elmelid","sequence":"first","affiliation":[{"name":"Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden"},{"name":"Department of Dermatology and Venereology, Falu Hospital, Region Dalarna, 791 82 Falun, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5899-5958","authenticated-orcid":false,"given":"Maria","family":"Siekkeri Vandikas","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden"},{"name":"Dermatology and Venereology Unit, Karolinska University Hospital, 171 76 Stockholm, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5033-5421","authenticated-orcid":false,"given":"Martin","family":"Gillstedt","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden"},{"name":"Department of Dermatology and Venereology, Sahlgrenska University Hospital, Region V\u00e4stra G\u00f6taland, 413 45 Gothenburg, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amra","family":"Osmancevic","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden"},{"name":"Department of Dermatology and Venereology, Sahlgrenska University Hospital, Region V\u00e4stra G\u00f6taland, 413 45 Gothenburg, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mikael","family":"Alsterholm","sequence":"additional","affiliation":[{"name":"Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden"},{"name":"Department of Dermatology and Venereology, Sahlgrenska University Hospital, Region V\u00e4stra G\u00f6taland, 413 45 Gothenburg, Sweden"},{"name":"Dermatology and Venereology Unit, Department of Medicine Solna, Karolinska Institutet, 171 76 Stockholm, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,6,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1945","DOI":"10.1001\/jama.2020.4006","article-title":"Pathophysiology, Clinical Presentation, and Treatment of Psoriasis: A Review","volume":"323","author":"Armstrong","year":"2020","journal-title":"JAMA"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"383","DOI":"10.1111\/ijd.12790","article-title":"The Role of Vitamin D in Psoriasis: A Review","volume":"54","author":"Soleymani","year":"2015","journal-title":"Int. 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Vitamin D-Binding Protein and the Free Hormone Hypothesis for Vitamin D in Bio-Na\u00efve Patients with Psoriasis. Int. J. Mol. Sci., 23.","DOI":"10.3390\/ijms23031302"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Martens, P.-J., Gysemans, C., Verstuyf, A., and Mathieu, A.C. (2020). Vitamin D\u2019s Effect on Immune Function. Nutrients, 12.","DOI":"10.3390\/nu12051248"},{"key":"ref_11","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_12","doi-asserted-by":"crossref","first-page":"1246","DOI":"10.1562\/2005-02-02-IR-430","article-title":"The Vitamin D3 Pathway in Human Skin and Its Role for Regulation of Biological Processes","volume":"81","author":"Lehmann","year":"2005","journal-title":"Photochem. 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