Sex Differences in Lifespan

Abstract

Sex differences in longevity can provide insights into novel mechanisms of aging, yet they have been little studied. Surprisingly, sex-specific longevity patterns are best known in wild animals. Evolutionary hypotheses accounting for longevity patterns in natural populations include differential vulnerability to environmental hazards, differential intensity of sexual selection, and distinct patterns of parental care. Mechanistic hypotheses focus on hormones, asymmetric inheritance of sex chromosomes and mitochondria. Virtually all intensively studied species show conditional sex differences in longevity. Humans are the only species in which one sex is known to have a ubiquitous survival advantage. Paradoxically, although women live longer, they suffer greater morbidity particularly late in life. This mortality-morbidity paradox may be a consequence of greater connective tissue responsiveness to sex hormones in women. Human females' longevity advantage may result from hormonal influences on inflammatory and immunological responses, or greater resistance to oxidative damage; current support for these mechanisms is weak.

Figure 1

Survival to age 5 and life expectancy at age 50 in Icelandic population cohorts born between 1840 and 1920. Note that female survival surpassed male survival in every year at both the beginning of life and later in life. Source: Human mortality database.