title: Early-life mortality risks in opposite-sex and same-sex twins: a Danish cohort study of the twin testosterone transfer hypothesis.
abstract: To investigate the twin testosterone transfer (TTT) hypothesis by comparing early-life mortality risks of opposite-sex (OS) and same-sex (SS) twins during the first 15 years of life.
  
  
  
  We performed a population-based cohort study to compare mortality in OS and SS twins. We included 68,629 live-born Danish twins from 1973 to 2009 identified through the Danish Twin Registry and performed piecewise stratified Cox regression and log-binomial regression.
  
  
  
  Among 1933 deaths, we found significantly higher mortality for twin boys than for twin girls. For both sexes, OS twins had lower mortality than SS twins; the difference persisted for the first year of life for boys and for the first week of life for girls.
  
  
  
  Although the mortality risk for OS boys was in the expected direction according to the TTT hypothesis, the results for OS girls pointed in the opposite direction, providing no clear evidence for the TTT hypothesis.
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark; Department of Public Health, Max-Planck Odense Center on the Biodemography of Aging, University of Southern Denmark, Odense C, Denmark. Electronic address: lahrenfeldt@health.sdu.dk.
authors.forename: Linda Juel
authors.initials: LJ
authors.lastname: Ahrenfeldt
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark.
authors.forename: Lisbeth Aagaard
authors.initials: LA
authors.lastname: Larsen
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark; Department of Public Health, Max-Planck Odense Center on the Biodemography of Aging, University of Southern Denmark, Odense C, Denmark.
authors.forename: Rune
authors.initials: R
authors.lastname: Lindahl-Jacobsen
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark.
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark.
authors.forename: Jacob V B
authors.initials: JV
authors.lastname: Hjelmborg
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark.
authors.forename: Sören
authors.initials: S
authors.lastname: Möller
authors.affiliation: Department of Public Health, The Danish Twin Registry, Unit of Epidemiology, Biostatistics and Biodemography, University of Southern Denmark, Odense C, Denmark; Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Odense C, Denmark; Department of Clinical Genetics, Odense University Hospital, Odense C, Denmark.
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
mesh_terms: D000293:Adolescent; D002423:Cause of Death; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D012044:Regression Analysis; D018570:Risk Assessment; D012737:Sex Factors; D013739:Testosterone / Q000097:blood*; D014429:Twins, Dizygotic / Q000706:statistics & numerical data*; D014430:Twins, Monozygotic / Q000706:statistics & numerical data*
chemical_list: D013739:Testosterone
keywords: Mortality; Opposite-sex; Same-sex; Sex; Twins