title: Sunlight is associated with decreased multiple sclerosis risk: no interaction with human leukocyte antigen-DRB1*15.
abstract: BACKGROUND
  Both insufficient exposure to sunlight and vitamin D deficiency have been associated with an increased risk for multiple sclerosis (MS). An interaction between human leukocyte antigen HLA-DRB1*15 and vitamin D in MS was recently proposed. We investigated the association between previous exposure to ultraviolet radiation (UVR), vitamin D status at inclusion in the study, and MS risk including the interaction of these factors with HLA-DRB1*15.
  
  
  METHODS
  A population-based case-control study involving 1013 incident cases of MS and 1194 controls was performed in Sweden during 2005-2010. Subjects were classified according to their UVR exposure habits, vitamin D status, and HLA genotypes. The associations between different sun exposure habits/vitamin D levels and MS were calculated as odds ratios (OR) with 95% confidence intervals (CI) using logistic regression. Potential interaction was evaluated by calculating the attributable proportion due to interaction.
  
  
  RESULTS
  Subjects with low UVR exposure had a significantly increased risk of MS compared with those who reported the highest exposure (OR 2.2, 95% CI 1.5-3.3). Similarly, subjects who had 25-hydroxy-vitamin D levels less than 50 nM/l had an increased risk for MS (OR 1.4, 95% CI 1.2-1.7). The association between UVR exposure and MS risk persisted after adjustment for vitamin D status. There was no interaction with HLA-DRB1*15 carriage.
  
  
  CONCLUSIONS
  UVR and vitamin D seem to affect MS risk in adults independently of HLA-DRB1*15 status. UVR exposure may also exert a protective effect against developing MS via other pathways than those involving vitamin D.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. maria.baarnhielm@karolinska.se
authors.forename: M
authors.initials: M
authors.lastname: Bäärnhielm
authors.forename: A K
authors.initials: AK
authors.lastname: Hedström
authors.forename: I
authors.initials: I
authors.lastname: Kockum
authors.forename: E
authors.initials: E
authors.lastname: Sundqvist
authors.forename: S A
authors.initials: SA
authors.lastname: Gustafsson
authors.forename: J
authors.initials: J
authors.lastname: Hillert
authors.forename: T
authors.initials: T
authors.lastname: Olsson
authors.forename: L
authors.initials: L
authors.lastname: Alfredsson
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D059811:HLA-DRB1 Chains / Q000009:adverse effects / Q000378:metabolism*; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics*; D011159:Population Surveillance / Q000379:methods; D012307:Risk Factors; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives / Q000378:metabolism / Q000502:physiology; D055815:Young Adult
chemical_list: D059811:HLA-DRB1 Chains; C507799:HLA-DRB1*15 antigen; D014807:Vitamin D; C104450:25-hydroxyvitamin D