User:C.Chung, Future PharmD/Health survival paradox

Female survival advantage
Records of the female survival advantage can be traced back to the 18th century, but gained popularity and caught the eyes of researchers in the 19th century. Women outlive men for all age groups and every year for which reliable records exist. Specifically in "contemporary industrialized countries", female survival is 1.5-2.0 times higher than that of males.

A female survival advantage is found in some, but not all species. Various explanations for this have been proposed, but none are strongly supported. Most species studied show conditional sex differences in life span, for males or females depending on the species in question. In humans, females appear to have a consistent survival advantage. Women outlive men in 176 of 178 countries for which records are available, both at age 5 and at age 50. The female survival advantage holds true among humans, but the same can not be said for baboons and birds. In a study conducted on Amboseli baboons, it was found that although females outlive their male counterparts similar to humans, both sexes had either similar rates of age-related declines in health, or greater health declines in males compared to females. Copied from Health survival paradox. In another study focused on Eurasian Blackbirds found lower survival in females due to more passive phenotypes that increased predation susceptibility.

A significant biological factor that may contribute to the female survival advantage is the difference in sex chromosome composition in males and females. The male sex is biologically defined by having one Y sex chromosome, and are heterogametic. While, females only have X chromosomes. Typically females have two X chromosomes, one active and one inactive, that can compensate one another for X chromosome gene mutations. In a longitudinal study following identical female twins and changes in X chromosome inactivation, skewed X chromosome inactivation patterns present at later stages of life suggested homologous sex chromosomes to benefit survival. Without multiple X chromosomes, males are more susceptible to X-linked diseases, or the effects of X chromosome mutations. These X-linked diseases include color blindness, hemophilia, and Duchenne's muscular dystrophy.

Male morbidity advantage
Women tend to report poorer health and more hospital visits than men. Women have more psychological disorders than men, but not more physical disorders. Women spend more years in good health than men. However, women spend more years in poor health than men as a proportion of their life expectancy. This implies that the male morbidity advantage is linked to the female survival advantage. Copied from Health survival paradox.