title: Sex and life expectancy.
abstract: BACKGROUND
  A sexual dimorphism in human life expectancy has existed in almost every country for as long as records have been kept. Although human life expectancy has increased each year, females still live longer, on average, than males. Undoubtedly, the reasons for the sex gap in life expectancy are multifaceted, and it has been discussed from both sociological and biological perspectives. However, even if biological factors make up only a small percentage of the determinants of the sex difference in this phenomenon, parity in average life expectancy should not be anticipated.
  
  
  OBJECTIVE
  The aim of this review is to highlight biological mechanisms that may underlie the sexual dimorphism in life expectancy.
  
  
  METHODS
  Using PubMed, ISI Web of Knowledge, and Google Scholar, as well as cited and citing reference histories of articles through August 2012, English-language articles were identified, read, and synthesized into categories that could account for biological sex differences in human life expectancy.
  
  
  RESULTS
  The examination of biological mechanisms accounting for the female-based advantage in human life expectancy has been an active area of inquiry; however, it is still difficult to prove the relative importance of any 1 factor. Nonetheless, biological differences between the sexes do exist and include differences in genetic and physiological factors such as progressive skewing of X chromosome inactivation, telomere attrition, mitochondrial inheritance, hormonal and cellular responses to stress, immune function, and metabolic substrate handling among others. These factors may account for at least a part of the female advantage in human life expectancy.
  
  
  CONCLUSIONS
  Despite noted gaps in sex equality, higher body fat percentages and lower physical activity levels globally at all ages, a sex-based gap in life expectancy exists in nearly every country for which data exist. There are several biological mechanisms that may contribute to explaining why females live longer than men on average, but the complexity of the human life experience makes research examining the contribution of any single factor for the female advantage difficult. However, this information may still prove important to the development of strategies for healthy aging in both sexes.
authors.affiliation: Faculty of Human Kinetics, Department of Kinesiology, University of Windsor, Windsor, Ontario, Canada.
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Seifarth
authors.forename: Cheri L
authors.initials: CL
authors.lastname: McGowan
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Milne
mesh_terms: D000375:Aging / Q000502:physiology; D001823:Body Composition; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism; D008017:Life Expectancy; D050356:Lipid Metabolism; D008297:Male; D018384:Oxidative Stress; D012727:Sex Characteristics; D013312:Stress, Physiological; D013315:Stress, Psychological / Q000378:metabolism; D049951:X Chromosome Inactivation
chemical_list: D012739:Gonadal Steroid Hormones; D006854:Hydrocortisone