title: Vitamin D serum level changes in psoriatic patients treated with narrowband ultraviolet B phototherapy are related to the season of the irradiation.
abstract: BACKGROUND
  Vitamin D is produced in the human skin by short wavelength (290-315 nm) ultraviolet (UV) radiation.
  
  
  OBJECTIVE
  The aim of the study was to investigate how outdoor conditions may influence the serum levels of 25(OH) vitamin D in psoriasis patients under narrowband ultraviolet B (UVB) phototherapy.
  
  
  METHODS
  The winter and summer groups of patients received almost the same narrowband UV (nUVB) doses during whole-body phototherapy. The 25(OH)D serum concentration was measured before and after two series of 10 exposures. The cabinet doses were compared with potentially available cumulative solar doses. The solar doses (unweighted UVB and vitamin D effective dose) and duration of solar intensity sufficient to produce vitamin D were calculated using a model based on local atmospheric data.
  
  
  RESULTS
  After an initial 10 nUVB treatments, 25(OH)D serum concentration increased by 68% for winter patients in relation to the level before therapy, whereas a 20% increase was found for the summer patients. The next 10 treatments caused a much lower increase in 25(OH)D concentration: 5% and 3.5% for the winter and summer patients, respectively. No statistically significant relationship was observed between post-therapy 25(OH)D serum concentration and solar radiation variability.
  
  
  CONCLUSIONS
  The different baseline values of 25(OH)D serum levels in winter and summer patients result from seasonal variability in solar irradiance. Thus, outdoor solar radiation affects the patients over a much longer period, and artificial UV light is the main factor responsible for increase in 25(OH)D serum level over a 30-day period of cabinet therapy.
authors.affiliation: Department of Dermatology, Medical University, Lodz, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Lesiak
authors.forename: Joanna
authors.initials: J
authors.lastname: Narbutt
authors.forename: Mariola
authors.initials: M
authors.lastname: Pawlaczyk
authors.forename: Anna
authors.initials: A
authors.lastname: Sysa-Jedrzejowska
authors.forename: Janusz
authors.initials: J
authors.lastname: Krzyścin
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011565:Psoriasis / Q000097:blood* / Q000532:radiotherapy*; D012621:Seasons; D013472:Sunlight; D013997:Time Factors; D014467:Ultraviolet Therapy; D014807:Vitamin D / Q000097:blood*
chemical_list: D014807:Vitamin D