title: Association of UV radiation with multiple sclerosis prevalence and sex ratio in France.
abstract: BACKGROUND
  French farmers and their families constitute an informative population to study multiple sclerosis (MS) prevalence and related epidemiology. We carried out an ecological study to evaluate the association of MS prevalence and ultraviolet (UV) radiation, a candidate climatologic risk factor.
  
  
  METHODS
  Mean annual and winter (December-March) UVB irradiation values were systematically compared to MS prevalence rates in corresponding regions of France. UVB data were obtained from the solar radiation database (SoDa) service and prevalence rates from previously published data on 2,667 MS cases registered with the national farmer health insurance system, Mutualité Sociale Agricole (MSA). Pearson correlation was used to examine the relationship of annual and winter UVB values with MS prevalence. Male and female prevalence were also analyzed separately. Linear regression was used to test for interaction of annual and winter UVB with sex in predicting MS prevalence.
  
  
  RESULTS
  There was a strong association between MS prevalence and annual mean UVB irradiation (r = -0.80, p < 0.001) and average winter UVB (r = -0.87, p < 0.001). Both female (r = -0.76, p < 0.001) and male (r = -0.46, p = 0.032) prevalence rates were correlated with annual UVB. Regression modeling showed that the effect of UVB on prevalence rates differed by sex; the interaction effect was significant for both annual UVB (p = 0.003) and winter UVB (p = 0.002).
  
  
  CONCLUSIONS
  The findings suggest that regional UVB radiation is predictive of corresponding MS prevalence rates and supports the hypothesis that sunlight exposure influences MS risk. The evidence also supports a potential role for gender-specific effects of UVB exposure.
authors.affiliation: Wellcome Trust Centre for Human Genetics and Department of Clinical Neurology, University of Oxford, Oxford, UK.
authors.forename: S-M
authors.initials: SM
authors.lastname: Orton
authors.forename: L
authors.initials: L
authors.lastname: Wald
authors.forename: C
authors.initials: C
authors.lastname: Confavreux
authors.forename: S
authors.initials: S
authors.lastname: Vukusic
authors.forename: J P
authors.initials: JP
authors.lastname: Krohn
authors.forename: S V
authors.initials: SV
authors.lastname: Ramagopalan
authors.forename: B M
authors.initials: BM
authors.lastname: Herrera
authors.forename: A D
authors.initials: AD
authors.lastname: Sadovnick
authors.forename: G C
authors.initials: GC
authors.lastname: Ebers
mesh_terms: D015897:Comorbidity; D003430:Cross-Sectional Studies; D004777:Environment; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology* / Q000378:metabolism / Q000503:physiopathology*; D015995:Prevalence; D012727:Sex Characteristics; D012867:Skin / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects; D014808:Vitamin D Deficiency / Q000453:epidemiology / Q000378:metabolism / Q000503:physiopathology