(“proximate”) factors are closer to the ends of causal chains. Upstream social factors that have repeatedly been linked with important health outcomes in many populations include income, accumulated wealth, educational attainment, and experiences based on racial or ethnic identification. Downstream factors (which may be shaped by upstream factors) include unhealthy diets, lack of exercise, and smoking. Features of neighborhoods and work environments may be thought of as midstream.

This chapter focuses on the social factors that current knowledge suggests may contribute significantly to the U.S. health disadvantage and that can be compared across high-income countries: income and poverty, income inequality, education, employment, social mobility, household composition, and experiences based on racial or ethnic identification (Galea et al., 2011; Link and Phelan, 1995; Marmot, 2005).

The chapter focuses primarily on social characteristics of individuals, families, and populations. The potential role of the social environment-—such as features of housing, transportation, and neighborhoods—in contributing to the U.S. health disadvantage is the focus of Chapter 7.

As in other chapters, the panel posed three questions:

•   Do social factors matter to health?

•   Are adverse social factors more prevalent in the United States than in other high-income countries?

•   Do differences in social factors explain the U.S. health disadvantage?

Before turning to these questions, however, we offer an important comment on evidence and the role of social factors on health. Documenting causality and testing the effectiveness of interventions for social factors is inherently challenging (Braveman et al., 2011b; Kawachi et al., 2010). The time intervals between exposures to social factors and a health outcome—such as the psychosocial consequences of poverty—may be quite long (Braveman et al., 2010a; Galobardes et al., 2008; Rychetnik et al., 2002). Exposures may occur during childhood, gestation, or even during the childhood of one’s parents (Hertzman, 1999; Kuh et al., 2002; Melchior et al., 2007; Turrell et al., 2007). Furthermore, the causal pathways from fundamental social causes to health outcomes are often complex, with opportunities for effect modification at multiple steps along the way (Braveman et al., 2010a). Relationships are also not unidirectional: cross-sectional associations do not clarify the role of reverse causality, as when poor health limits education or income. Adverse health and socioeconomic circumstances can also negatively affect household stability, family composition, and social support. Because it would be both difficult, if not unethical, to test these hypotheses in randomized controlled

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