Sex Differences in Infant and Early Childhood Mortality: Major Causes of Death and Possible Biological Causes
Citation: Waldron (1996) Sex Differences in Infant and Early Childhood Mortality: Major Causes of Death and Possible Biological Causes.
In developing countries, males have consistently higher mortality than females during the neonatal period. Sex differences in mortality are more variable during the post-natal period of infancy, and by early childhood, females have higher mortality than males in many developing countries. That shift from a consistent male excess to more variable sex differences in mortality is due in part to a shift with age in the major causes of death that contribute to total mortality. In the neonatal period, excess male mortality is due to perinatal conditions. In addition, males generally have higher mortality for congenital anomalies, which makes an additional but modest contribution to higher male neonatal mortality.
During early childhood, infectious diseases and accidents are the biggest contributors to sex differences in mortality. Boys have higher accident mortality than girls in almost all countries. This finding may be related to the prenatal exposure of males to higher levels of testosterone which are reinforced by differences in the socialization in most cultures.
Within the categories of congenital anomalies and infectious diseases, sex differences are variable. Males have higher mortality risk than females from many types of congenital anomalies, but females have higher mortality risk from congenital anomalies on the central nervous system. Sex differences in infectious disease mortality vary with age group, environmental conditions and specific type of infectious disease. In infancy, males generally have higher mortality than females from mortality types of infectious disease, whereas for young children sex differences are more variable and appear to be influenced by environmental factors, such as discrimination against females. For measles, females have tended to have higher mortality than males.
The biological factors that contribute to sex differences in various causes of death are diverse, and to date only poorly understood. Consistently higher male mortality for perinatal conditions is most likely due to inherent biological disadvantages. Biological disadvantages for males may include greater risk of birth at younger gestational ages, greater immaturity of males' lungs at given gestational age, and other factors that have not yet been identified. It appears that ht biological disadvantages for males are sufficient to outweigh one well-established male advantage their higher birthweights. The causes of sex differences in congenital anomalies mortality are poorly understood, but it appears that they are influenced by multiple sex differences in development, some of which favor females and others males. It appears likely that inherent sex differences in biology contribute to sex differences in infectious disease mortality, although evidence is limited and inconsistent. Immune resistance among males may be reduced by X-linked genetic defects; however, they are very rare. Immune function among males may also be inhibited by exposure to testosterone during the prenatal period and early infancy; however, the mechanism is unclear. In general, males may have inherent disadvantages in resistance to infectious disease, but additional evidence will be required to evaluate the extent and nature of the male disadvantage in different age groups, for different types of infectious disease and under different environmental circumstances. Available evidence suggests that males have inherently greater vulnerability for mortality due to perinatal conditions and for total mortality in the neonatal period, but the assumption that males have a pervasive inherent disadvantage is incorrect for some types of congenital anomalies, and is of uncertain validity for infectious diseases and total mortality in early childhood.