Social context as an explanation for race disparities in hypertension: Findings from the Exploring Health Disparities in Integrated Communities (EHDIC) Study
Introduction
Approximately 65 million adults in the United States have hypertension (Fields et al., 2004). African Americans tend to have earlier onset, higher prevalence and more severe hypertension than do non-Hispanic whites (Burt et al., 1995, Klag et al., 1997). Hypertension is an important risk factor for several vascular diseases including coronary heart disease, stroke, heart failure and kidney disease (Klag et al., 1996, Levy et al., 1996, MacMahon et al., 1990, Slama et al., 2002, Stamler et al., 1993, Whelton et al., 1992, Whelton et al., 2002). African Americans have a greater risk of cardiovascular disease mortality compared with non-Hispanic whites, and most of this risk is attributable to hypertension (Bravata et al., 2005, Wong et al., 2002).
Most of the research examining factors that underlie race differences in hypertension prevalence posit individual-level explanations. For example, some studies indicate that the higher prevalence of hypertension observed in African Americans is inversely associated with socioeconomic status (Colhoun, Hemingway, & Poulter, 1998), while other studies suggest that psychosocial factors such as discrimination may explain the race difference (Brondolo et al., 2003, Myers and McClure, 1993, Williams and Neighbors, 2001). Krieger and Sidney (1996) found that perceived discrimination and unfair treatment largely accounted for the racial differences in blood pressure. Physical inactivity has also been posited as an explanation for the association between race and hypertension. However, Bassett, Fitzhugh, Crespo, King, and McLaughlin (2002) found that African Americans who had a higher age-adjusted prevalence of hypertension across all levels of physical activity and even within the same level of physical activity. In general these individual-level factors have been able to explain some of the race disparity in hypertension, but a substantial amount of the disparity remains unexplained.
No previous study has examined the possibility that race differences in social context in which African Americans and non-Hispanic whites live may contribute to disparities. It is possible that race differences in hypertension result from race differences in social and environmental exposures resulting from residential segregation (LaVeist, 2005b). Non-Hispanic whites and African Americans tend to live in very different social environments. Studies of racial residential segregation have found that upwards of 60% of African Americans would need to move to another census tract in order to achieve complete integration between African Americans and non-Hispanic white Americans (Iceland et al., 2002, Massey and Denton, 1993). This extreme racial segregation contributes to race differences in social and environmental health risk exposures (LaVeist, 2005a, LaVeist, 2005b). Direct tests of the segregation-health disparities hypothesis have found associations between segregation and a variety of outcomes including, infant mortality (LaVeist, 1989, LaVeist, 1993), adult mortality (Collins and Williams, 1999, Fang et al., 1998, Jackson et al., 2000, Polednak, 1996), tuberculosis (Acevedo-Garcia, 2001), hospital admissions (Hart, 1997), availability of supermarkets (Morland, Wing, Diez Roux, & Poole, 2002), and availability of pharmaceuticals (Morrison, Wallenstein, Natale, Senzel, & Huang, 2000).
Racial segregation is an important, yet understudied, determinant of health disparities which may complicate the ability of national data to produce truly similar groups appropriate for comparisons (LaVeist, Thorpe, Mance, & Jackson, 2007). Failure to account for race differences in health risk exposures resulting from segregation can potentially lead to erroneous conclusions about the etiology of racial disparities in health. For example differences demonstrated in national data may be the result of differential environmental risk exposures, but erroneously ascribed as a direct effect of race. This may contribute to widely held beliefs about biological explanations for race disparities and possibly even an overemphasis on cultural differences causing race differences in health behaviors.
Another complicating factor for race disparities in hypertension research is the well-documented association between race and socioeconomic status (SES). Race and SES are highly correlated and both are predictors of hypertension. Typically this problem is addressed by using multivariate modeling in national samples to simultaneously specify the effects of race and measures of SES (such as income or education) on a dependent variable. However, this approach may be inadequate (LaVeist et al., 2007). Even after adjusting for income and education, there are remaining unmeasured differences in SES between race groups owing to historical discrimination and intergenerational transfers of wealth. Multivariate modeling may not be sufficient to overcome this source of heterogeneity (Braveman et al., 2005, LaVeist, 2005a). Moreover, even in a large national survey multivariate modeling may lead to biased results because of small cell sizes in some race/SES groupings. For example, small numbers of low income whites or high income blacks (see LaVeist et al., 2007 for a more detailed illustration of this issue).
Accounting for social and environmental factors may reveal important insights into the nature of inequalities between black and white adults in health outcomes such as hypertension. The objective of this report is to examine the association between race and hypertension in a sample of African American and non-Hispanic white adults with similar income status, dwelling in the same social context. Within such a community setting, we can account for unmeasured heterogeneity associated with living within a different social context, which is not possible in national samples which suffer from the complex interplay between race, SES and segregation (Braveman et al., 2005, Conley, 1999, Hodge et al., 2007, Kaufman et al., 1997, LaVeist, 2005a, LaVeist, 2005b, Oliver and Shapiro, 1995, Raich and Rich, 2002). We compared results of analytic models in our sample (Exploring Health Disparities in Integrated Communities or EHDIC) with those from a national sample (NHANES 1999–2004) to determine whether disparities in hypertension differed within a context where black and white Americans live under similar social conditions. Specifically, we hypothesized that black-white disparities in hypertension will be attenuated after accounting for race-SES confounding and the different environmental contexts in which whites and blacks typically live.
Section snippets
Populations
EHDIC (Exploring Health Disparities in Integrated Communities) is an ongoing multisite study of race disparities within communities where African Americans and non-Hispanic whites live together and where there are no race differences in SES (as measured by median income). The first EHDIC Study site was in southwest Baltimore, Maryland (EHDIC-SWB). Future EHDIC locations are planned.
To have a neighborhood that is racially integrated and homogenous in regard to on income makes this sample quite
Results
A unique aspect of the EHDIC-SWB is the similarity of demographic and health-related characteristics between African American and non-Hispanic whites, which is not the case in NHANES or any nationally representative sample. By design EHDIC-SWB and NHANES are quite different; however, it is instructive to specify the ways in which the samples differ. Table 1 displays the demographic characteristics of the EHDIC-SWB and NHANES samples. As expected the African Americans and non-Hispanic whites in
Discussion
We examined the association between race and hypertension in the EHDIC-SWB sample, a survey of African American and non-Hispanic white adults living in similar socioeconomic and socio-environmental circumstances. We hypothesized that race differences in hypertension would be attenuated in EHDIC-SWB compared with NHANES because of the similarity of the social context in which the EHDIC-SWB respondents live. Using multiple logistic regression models, we found that the ethnic disparity in
Acknowledgements
This research was supported by grant # P60MD000214-01 from the National Center on Minority Health and Health Disparities (NCMHD) of the National Institutes of Health (NIH), and a grant from Pfizer, Inc. Dr. Thorpe was supported by a training grant from the National Institute on Aging (T32AG000120) and contract from the National Center for Minority Health and Health Disparities Loan Repayment Program.
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