Social Determinants of Health: Future Directions for Health Disparities Research

In 2015, the National Institutes on Minority Health and Health Disparities (NIMHD) engaged in a two-year science visioning process for health disparities and convened a series of workshops aimed at identifying promising research directions. A central theme that resonated throughout these workshops was the importance of social determinants of health and their relationship to health disparities. Broadly defined, social determinants of health represent economic and political structures, social and physical environments, and access to health services.¹ Although observational research has documented the influence of social determinants on actual health, unanswered questions surrounding the mechanisms that explain why those who are socially disadvantaged suffer disproportionality from disease- and health-related burden remain. This editorial summarizes key research directions that emerged from NIMHD’s science visioning and are aimed at developing a more robust understanding of how social determinants of health contribute to health disparities. These research directions include

• 1. understanding the contributions of upstream social determinants of health,

• 2. embodiment,

• 3. protective factors and resiliency,

• 4. place and context, and

• 5. overcoming methodological challenges.

UPSTREAM SOCIAL DETERMINANTS OF HEALTH

A fair amount of research has investigated mid- and downstream social determinants of health (e.g., education, neighborhood condition, risk behaviors, and access to health care) and their relationship to health outcomes and health disparities, but research elucidating how upstream social determinants of health (e.g., governance and policy) shape pathways that lead to health disparities is needed. Research is needed that focuses attention farther upstream and explains how social and economic policies set in motion a progression of steps that limit and restrict and ultimately result in health disparities. Further, research investigating how upstream factors, such as governance and legislation, create structural challenges and impose downstream barriers that impact the ability and opportunity to lead a healthy lifestyle is also warranted. Additionally, upstream research must also account for racism and discrimination.² Racism and discrimination have not only shaped economic and social policies in the United States but also directly influenced the lived experiences of racial and ethnic minorities.

EMBODIMENT

Identifying how adverse exposures affect the body and how they lead to illness and disease is an area rich for exploration. Central to this line of inquiry is understanding how social stress “gets under the skin.” To date, several mechanisms have been proposed that focus on the physiological effects of chronic stress. They include (1) dysregulation of physiological systems (e.g., hypothalamic pituitary adrenal–cortisol axis, allostasis and allostatic load, and weathering), (2) epigenetic modifications (e.g., DNA methylation, histone modification, and chromatin and telomere structure), (3) the metabolome and microbiome, and (4) immune and inflammation response. These proposed mechanisms present plausible physiological explanations of how the body responds to chronic stress created by social determinants of health. However, challenges exist in making the connection between social determinants and the body. For example, the time between exposure and physiological response is unknown. Perhaps the largest challenge for embodiment research is trying to estimate the difference between physiologic processes that normally occur in human systems responding to daily stress versus those that are influenced by social inequity.

PROTECTIVE FACTORS AND RESILIENCE MECHANISMS

Despite exposure to adverse social determinants of health, not all individuals, families, communities, or populations experience worse health outcomes. Protective social factors (e.g., social support) are hypothesized to prevent or modulate the deleterious effects, while resilience mechanisms allow for adaptive functioning in response to adverse exposures.³ A key research question is to what extent do protective factors and mechanisms of resilience explain why some individuals, groups, and populations withstand adverse social determinants of health. Thus, an important avenue of research is identifying protective social factors and mechanisms of resilience and how they work in and across different populations. Furthermore, understanding how protective social factors and mechanisms for resiliency operate at the individual, family, community, and societal levels is warranted and can potentially be used as strategies to reduce health disparities.

PLACE AND CONTEXT

Neighborhoods, a place where people live, play, work, and receive health care, are understood as a convergence between the built and social environments and has been shown to contribute to morbidity and mortality.⁴ Although minorities and low socioeconomic status populations disproportionately live in resource poor communities, there is great variability among these communities. For instance, life expectancy can vary substantially across areas in the United States,⁵ yet reasons for this variation are not clearly known. Although upstream social determinants of health may structure place and context, there is much to be learned about how place and context contribute to health disparities. Although mechanisms have been proposed to account for geographically clustered health disparities, such as differential exposures to environmental toxins, communities with low material and social support, higher concentrations of social stressors (e.g., violence, economic instability), constrained lifestyles (e.g., high density of tobacco and alcohol outlets or food deserts), and psychosocial mechanisms that influence health behaviors, opportunities are needed that elucidate why place matters and how it contributes to health disparities.

METHODOLOGICAL CHALLENGES

It is widely believed that health disparities are the outcome of multiple causes operating at multiple levels in multiple domains—economic, social policies, environment, access to health care, behavior, and biology—that play out over a long period of time. Unfortunately, these complex multifactorial pathways do not lend themselves to testing easily. New analytic and methodological approaches are needed. Complex systems modeling is one such approach that has gained interest and can generate hypotheses examining how changes in systems either perpetuate or reduce health disparities.⁶ Finally, models need to account for cumulative risk. It is not just one social risk factor, but rather a multitude of social factors that are more likely responsible.

Even if pathways can be empirically tested, issues exist with establishing causality. Much of the research on social determinants of health is observational. To make progress in eliminating disparities, we need more than a “yes” or “no” judgment about the effects of social determinants of health; we need precise, pathway-specific quantitative estimates. Study designs that better account for establishing causality, and take into account bias and confounding, are needed. Finally, work is needed to address the limitations of the variables and measures used in research involving social determinants of health. A set of acceptable and relevant variables and objective measures should be identified for consistent collection and data sharing. Convenient indicators like “achieved education” and “annual household income” reflect entrenched patterns of exclusion and power.

FUTURE DIRECTIONS

Understanding why population groups who experience social disadvantage disproportionally experience worse health outcomes has been a central focus of health disparities research. Convincing scientific evidence has highlighted the impact of social determinants of health on population health and health disparities; however, the mechanisms and pathways involving social determinants of health and how they lead to health disparities is still not clear. Emerging from NIMHD’s science vision is a research direction that moves away from observational research, and ventures toward identifying mechanisms and pathways that can explain how social determinants impact health and lead to health disparities. Understanding how upstream social determinants of health influence the lived experience, how the body responds to social stress, how social and protective factors influence health, and how place can affect health are critical pieces of the puzzle that need to be understood. Additionally, opportunities for methodological advances exist and are needed to allow for better distinction and identification of causal social factors related to health disparities. If a better understanding of the causes of health disparities can be achieved, especially the role played by social determinants of health, effective interventions can be developed, and ultimately, reductions in health disparities achieved.