title: Geographic variation in the prevalence of attention-deficit/hyperactivity disorder: the sunny perspective.
abstract: BACKGROUND
  Attention-deficit/hyperactivity disorder (ADHD) is the most common psychiatric disorder of childhood, with average worldwide prevalence of 5.3%, varying by region.
  
  
  METHODS
  We assessed the relationship between the prevalence of ADHD and solar intensity (SI) (kilowatt hours/square meters/day) on the basis of multinational and cross-state studies. Prevalence data for the U.S. were based on self-report of professional diagnoses; prevalence data for the other countries were based on diagnostic assessment. The SI data were obtained from national institutes.
  
  
  RESULTS
  In three datasets (across 49 U.S. states for 2003 and 2007, and across 9 non-U.S. countries) a relationship between SI and the prevalence of ADHD was found, explaining 34%-57% of the variance in ADHD prevalence, with high SI having an apparent preventative effect. Controlling for low birth weight, infant mortality, average income (socioeconomic status), latitude, and other relevant factors did not change these findings. Furthermore, these findings were specific to ADHD, not found for the prevalence of autism spectrum disorders or major depressive disorder.
  
  
  CONCLUSIONS
  In this study we found a lower prevalence of ADHD in areas with high SI for both U.S. and non-U.S. data. This association has not been reported before in the literature. The preventative effect of high SI might be related to an improvement of circadian clock disturbances, which have recently been associated with ADHD. These findings likely apply to a substantial subgroup of ADHD patients and have major implications in our understanding of the etiology and possibly prevention of ADHD by medical professionals, schools, parents, and manufacturers of mobile devices.
authors.affiliation: Department of Experimental Psychology, Utrecht University, Utrecht, the Netherlands; Research Institute Brainclinics, Nijmegen, the Netherlands. Electronic address: martijn@brainclinics.com.
authors.forename: Martijn
authors.initials: M
authors.lastname: Arns
authors.forename: Kristiaan B
authors.initials: KB
authors.lastname: van der Heijden
authors.forename: L Eugene
authors.initials: LE
authors.lastname: Arnold
authors.forename: J Leon
authors.initials: JL
authors.lastname: Kenemans
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology*; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D012993:Solar Energy; D014481:United States; D055815:Young Adult
keywords: ADHD; chronobiological; circadian; light; prevalence; solar intensity