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There is growing epidemiologic evidence of differing associations between air pollution and respiratory health for females and males. More studies report stronger effects among women and girls than among men and boys, but the literature is far from consistent. Importantly, it is unknown whether observed modification is attributable primarily to biological differences between men and women, to exposure differences (e.g., work-related coexposures), or to some interplay thereof. Gender analysis, which aims to disaggregate social and biological differences between men and women (e.g., hormonal status), may help to elucidate this modification, identify key mechanisms, and design more effective interventions.
The distinction between gender (i.e., self-representation, socially derived activities and roles) and sex (i.e., biological differences by chromosomal complement, including reproductive organs and hormonal composition) (Krieger 2003) speaks to the distinction between exposure and susceptibility. Gender analysis is more common in occupational epidemiology (Arbuckle 2006; Messing and Stellman 2006; Messing et al. 2003; Schachter et al. 2009) than in environmental health (Keitt et al. 2004), because persistent job stratification by sex (Alexanderson and Östlin 2001) has produced marked differences in occupational exposures to chemical agents (Hursidic-Radulovic et al. 2002; London et al. 2002), ergonomic demands (Silverstein et al. 1986), injury (Salminen et al. 1992), and psychosocial stressors (Arcand et al. 2000; Bourbonnais et al. 2000; Gutek 2001; Hall 1989).
Gender, a social construct, includes cultural norms, roles, and behaviors shaped by relations among women and men and among girls and boys (Krieger 2003). Gender, inherently social, varies continuously over multiple dimensions over the life course, whereas sex is normally dichotomous. Gender is shaped at the societal level and varies across nation, culture, class, race, ethnicity, nationality, sexuality, and religion. Gender describes patterns of behavior, place, and role, determining where people spend time and their activities, thereby shaping exposure distributions.
Sex, a biological construct, is based on physiologic differences enabling reproduction, defined by physiologic characteristics (especially reproductive organs) or chromosomal complement (Krieger 2003). Sex-linked traits (e.g., hormonal status, body size) influence biological transport of environmentally derived chemicals. Lung size and growth, deposition of fine particles [particulate matter ≤ 2.5 µm in aerodynamic diameter (PM2.5)] (Kim and Hu 1998, 2006), gas absorption (Jones and Lam 2006), gasblood barrier permeability (Brauner et al. 2009), airway hyperresponsiveness (Kanner et al. 1994), vascular response (Prisby et al. 2008), and inflammation (Hermes et al. 2006; Sood et al. 2008) all differ, on average, by sex.
Sex and gender can be difficult to distinguish in epidemiologic data; they are tightly intertwined, with reciprocal effects. Biological characteristics (e.g., body size) become engendered as occupational and family roles, which are gendered expressions of biology. Likewise, gendered work and caregiving roles, smoking, and alcohol consumption influence muscle mass, adiposity, and chemical body burden—collectively, these are socially derived biological expressions of gender (Krieger 2003).
In this review I present a framework for incorporating gender analysis into air pollution epidemiology, describing pathways through which gender and sex, separately and multiplicatively, may influence pollution response. Current evidence of effect modification in air pollution respiratory epidemiology is summarized, and potentially useful nascent analytic methods from gender analysis are offered.
Gender analysis explores topics far beyond those addressed here, including sexuality and transgender issues. Here I consider only those constructs and tools that may directly inform mean differences between men and women in air pollution epidemiology.