title: Association of type 1 diabetes with month of birth among U.S. youth: The SEARCH for Diabetes in Youth Study.
abstract: OBJECTIVE
  Seasonal environment at birth may influence diabetes incidence in later life. We sought evidence for this effect in a large sample of diabetic youth residing in the U.S.
  
  
  METHODS
  We compared the distribution of birth months within the SEARCH for Diabetes in Youth Study (SEARCH study) with the monthly distributions in U.S. births tabulated by race for years 1982-2005. SEARCH study participants (9,737 youth with type 1 diabetes and 1,749 with type 2 diabetes) were identified by six collaborating U.S. centers.
  
  
  RESULTS
  Among type 1 diabetic youth, the percentage of observed to expected births differed across the months (P = 0.0092; decreased in October-February and increased in March-July). Their smoothed birth-month estimates demonstrated a deficit in November-February births and an excess in April-July births (smoothed May versus January relative risk [RR] = 1.06 [95% CI 1.02-1.11]). Stratifications by sex or by three racial groups showed similar patterns relating type 1 diabetes to month of birth. Stratification by geographic regions showed a peak-to-nadir RR of 1.10 [1.04-1.16] in study regions from the northern latitudes (Colorado, western Washington State, and southern Ohio) but no birth-month effect (P > 0.9) in study regions from more southern locations. Among type 2 diabetic youth, associations with birth month were inconclusive.
  
  
  CONCLUSIONS
  Spring births were associated with increased likelihood of type 1 diabetes but possibly not in all U.S. regions. Causal mechanisms may involve factors dependent on geographic latitude such as solar irradiance, but it is unknown whether they influence prenatal or early postnatal development.
authors.affiliation: Division of Diabetes Translation, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. hkahn@cdc.gov
authors.forename: Henry S
authors.initials: HS
authors.lastname: Kahn
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Morgan
authors.forename: L Douglas
authors.initials: LD
authors.lastname: Case
authors.forename: Dana
authors.initials: D
authors.lastname: Dabelea
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Mayer-Davis
authors.forename: Jean M
authors.initials: JM
authors.lastname: Lawrence
authors.forename: Santica M
authors.initials: SM
authors.lastname: Marcovina
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Imperatore
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D044469:Racial Groups / Q000706:statistics & numerical data; D012621:Seasons; D014481:United States / Q000453:epidemiology
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