Association of type 1 diabetes with month of birth among US youth: The SEARCH for Diabetes in Youth Study

  1. Henry S. Kahn, MD (hkahn{at}cdc.gov)1,
  2. Timothy M. Morgan, PhD2,
  3. L. Douglas Case, PhD2,
  4. Dana Dabelea, MD, PhD3,
  5. Elizabeth J. Mayer-Davis, PhD4,
  6. Jean M. Lawrence, ScD, MPH, MSSA5,
  7. Santica M. Marcovina, PhD, ScD6,
  8. Giuseppina Imperatore, MD, PhD1 and
  9. for the SEARCH for Diabetes inYouth Study Group
  1. 1– Division of Diabetes Translation, Centers for Disease Control and Prevention, Atlanta, GA
  2. 2– Department of Biostatistical Sciences, Division of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, NC
  3. 3– Department of Epidemiology, Colorado School of Public Health, University of Colorado Denver, Aurora CO
  4. 4– Center for Research in Nutrition and Health Disparities, University of South Carolina, Columbia, SC, and Department of Nutrition, University of North Carolina, Chapel Hill, NC
  5. 5– Department of Research & Evaluation, Kaiser Permanente Southern California, Pasadena, CA 91101
  6. 66 – Department of Medicine, University of Washington, Seattle, WA 98109 USA

    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 US.

    Research design and methods – We compared the distribution of birth months within the SEARCH for Diabetes in Youth Study with the monthly distributions in US births tabulated by race for years 1982–2005. SEARCH participants (9,737 youth with type 1 and 1,749 with type 2 diabetes) were identified by 6 collaborating US centers.

    Results – Among type 1 diabetic youth the percentage of observed to expected births differed across the months (P = .0092; decreased in October-February, 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 vs January relative risk [RR]=1.06 (95% CI 1.02–1.11)). Stratifications by sex or by 3 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 (CI 1.04–1.16) in study regions from 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 US 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.

    Footnotes

      • Received May 14, 2009.
      • Accepted August 6, 2009.

    This Article

    1. Diabetes Care
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