and importance of racial differences in genetic effects, particularly for complex diseases” (Ioannidis et al., 2004).

Previous chapters have discussed the contributions of the social environment, behavior, psychological factors, physiological mechanisms, and genetic variation to health. This chapter highlights the fact that the contributions of these variables are not monolithic and that fundamental individual traits, such as sex/gender and race/ethnicity, can change their meaning and health impact in different contexts. These complex traits are multifaceted, and the goal is to tease apart the facets at different levels of organization in order to identify which of them directly modulate health. This is a reciprocal process, because these various domains in turn inform our understanding of sex/gender and race/ethnicity. Failing to distinguish these different facets, both in the aggregate and within each level of analysis, will compromise the ability to obtain a more fine-grained understanding of how the different aspects of these fundamental individual traits interact to influence health.

SEX/GENDER

Although the terms sex and gender are often used interchangeably, they, in fact, have distinct meanings. Sex is a classification based on biological differences—for example, differences between males and females rooted in their anatomy or physiology. By contrast, gender is a classification based on the social construction (and maintenance) of cultural distinctions between males and females. Gender refers to “a social construct regarding culture-bound conventions, roles, and behaviors for, as well as relations between and among, women and men, boys and girls” (Krieger, 2003).

Differences in the health of males and females often reflect the simultaneous influence of both sex and gender. Not only can gender relations influence the expression of biological traits, but also sex-associated biological characteristics can contribute to amplify gender differentials in health (Krieger, 2003). The relative contributions of gender relations and sex-linked biology to health differences between males and females depend on the specific health outcome under consideration. In some instances, sex-linked biology is the sole determinant of a health outcome—for example gonadal digenesis among women with Turner’s syndrome (due to X-monosomy). In other instances, gender relations account substantially for observed gender differentials for a given health outcome—for example the higher prevalence of needle-stick injuries among female compared to male health care workers, which is in turn attributed to the gender segregation of the health care workforce. The prevalence of HIV infection through needle-stick injury is higher among female health care workers because the majority of doctors are men, the majority of nurses and phlebotomists are women,



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