Social determinants of health status.

Socioeconomic status (SES) has been identified as a fundamental cause of disease (Link & Phelan, 1995, 1996; Phelan et al., 2004; Phelan, Link, & Tehranifar, 2010). People who are poor and powerless have worse health and longevity than those with money, power, and prestige. This situation was true during the times when infectious diseases were major killers and there was poor sanitation and overcrowding. It is equally true today when infectious diseases and crowding are no longer a threat in the US, but instead cancers and heart disease are the major causes of morbidity and mortality. People with lower SES continue to be the group that experiences the highest rates of morbidity and age-adjusted mortality from these more modern diseases, stimulated by risk factors such as poor nutrition, lack of exercise, and smoking that are more common in lower SES groups (Phelan et al., 2010). In order to explain this persistence across time, Link and Phelan (1995) proposed the theory that social conditions were the fundamental cause of the health disparities that exist between people without socioeconomic resources and those with these resources. It is instructive to revisit the fundamental social cause theory of health disparities and to review the evidence that has accumulated supporting it over the years. Socioeconomic status as a fundamental cause of health inequalities has four essential features (Link & Phelan, 1995). First, it influences multiple disease outcomes, meaning that SES is not limited to only one or a few diseases or health problems but to many. Second, SES affects these disease outcomes through multiple risk factors (currently things such as smoking, diet, exercise). Third, it involves access (or lack of access) to resources that can be used to avoid risks or to minimize the consequences of disease once it occurs. Finally, the association between a fundamental cause and health status is reproduced over time via the replacement of intervening predisposing factors (e.g., overcrowding and poor sanitation replaced by lifestyle choices and behaviors); that is, SES continues to influence health inequalities even when the susceptibilities to major morbidity and mortality change over time (Link & Phelan, 1995). An important reason that SES is related to multiple disease outcomes through multiple pathways that change over time is that individuals and groups with high SES deploy resources to avoid risks and adopt protective strategies. Link and Phelan (1996) identified money, knowledge, power, prestige, and beneficial social connections as the serviceable resources that people with high SES mobilize purposefully to avoid risks and minimize the consequences of disease once it occurs. These resources can be used no matter what the risk may be or the protective behaviors called for in any given circumstance. Therefore, fundamental causes affect health even when the profile of risks, protective factors, and disease expression changes completely. It is the consistent association of SES with overall health status in the face of dramatic changes in the predisposing factors to disease that led Link and Phelan to call SES a “fundamental” cause of health inequalities (Phelan et al., 2010). Despite the researchers having spent over 15 years developing, explaining, testing, and demonstrating evidence of the link between SES and morbidity and mortality, it is still misunderstood by many in the scholarly and research communities. This fact came home to me again recently in dealing with a young colleague who was searching for a theoretical framework to explain the disproportionate occurrence of hypertension in African Americans. This colleague was not advised to examine socially-based determinants of health as explanatory variables, but only individually-based determinants such as diet and exercise. When the vulnerable populations conceptual model was proposed in the late 1990s, I (Flaskerud) was often frustrated by my inability to persuade my associates of the explanatory value of “availability of resources” (money, status, social connections) in predicting health status (Flaskerud & Winslow, 1998). My colleagues were skeptical of the important influence of resources and would call them “the demographics—I know—we measure those.” In Link and Phelan’s (1995) case, medical and epidemiologic researchers dismissed SES as a less critical confounding variable and focused on lifestyle factors as the explanation for inequalities in health status. When Link and Phelan (1995) described SES as a fundamental cause of health disparities, they acknowledged the gains that medical science has made in identifying risk factors for major diseases. However, they observed that most of this research has focused attention on risk factors that they identified as relatively proximal causes of disease such as diet, cholesterol level, exercise, and the like. They argued that there is a lack of context in this emphasis on such individually-based risk factors and that greater attention must be paid to basic social conditions: low economic and social status (SES), powerlessness, and lack of beneficial social connections. They identified these social conditions as distal factors—those that put people at risk of risks. Social conditions are fundamental causes of health disparities because they are primary (occur first), exemplify access to important resources, affect multiple disease outcomes through multiple risk factors, and maintain an association with disease even when intervening predisposing factors change. Socioeconomic status is a fundamental cause of health disparities because SES embodies an array of flexible resources, such as money, knowledge, prestige, power, and beneficial social connections that protect health no matter what the major predisposing factors of morbidity and mortality are at any given time (Link & Phelan, 1995; Phelan et al., 2004; Phelan et al., 2010). First writing at the time of President Clinton’s attempt at health care reform, Link and Phelan (1995, 1996) were interested in identifying the critically missing factors that they theorized were necessary to craft effective interventions and improve the nation’s health. They were concerned that without careful attention to the social determinants of health, we as a country would run the risk of imposing individually-based intervention strategies that are ineffective and that we would miss the opportunity to adopt broad-based societal interventions that could produce substantial health benefits for our citizens. Through the intervening years, between the 1990s and the present, Phelan, Link, and colleagues (2004, 2010) have worked consistently to test their theory and to provide evidence supporting it. Empirical support for the theory lies in examining evidence of each of the four essential features of SES as a fundamental cause: (1) evidence that SES influences multiple disease outcomes; (2) evidence that SES is related to multiple risk factors for disease and death; (3) evidence that the mobilization of resources plays a crucial role in the association between SES and disease prevention and treatment and longevity; and (4) evidence that the association between SES and morbidity and mortality continues over time, even when the major predisposing factors to disease and death change with advances in public health and medicine.