摘要：Objectives. We explored the notion that social disadvantage increases vulnerability to the health effects of environmental hazards. Specifically, we examined (1) whether race modifies the association between blood lead and blood pressure and (2) whether socioeconomic status (SES) plays a role in this modifying effect. Methods. Using the National Health and Nutrition Examination Survey (2001–2008) and linear regression, we estimated the association between blood lead and blood pressure. Using interactions among race, SES, and lead, we estimated this association by levels of social disadvantage. Results. Black men and women showed a 2.8 ( P < .001) and 4.0 ( P < .001) millimeters mercury increase in SBP, respectively, for each doubling of blood lead. White adults showed no association. This lead–SBP association exhibited by Blacks was primarily isolated to Blacks of low SES. For example, poor but not nonpoor Black men showed a 4.8 millimeters mercury ( P < .001) increase in SBP for each doubling of blood lead. Conclusions. Our results suggest that social disadvantage exacerbates the deleterious health effects of lead. Our work provides evidence that social and environmental factors must be addressed together to eliminate health disparities. Black–White disparities in hypertension have been well-documented for decades. 1–3 A 2010 American Heart Association report put nationwide prevalence estimates at roughly 33% for White adults but 43% for Black adults. 4 Economically, if Black Americans had the hypertension rates of White Americans, about $400 million would have been saved in out-of-pocket health care expenses, about $2 billion would have been saved in private insurance costs, and $375 million would have been saved from Medicare and Medicaid—per year. 5 More seriously, disparities are also seen in outcomes related to hypertension. For example, mortality rates because of hypertension are roughly 15 deaths per 100 000 people for White men and women; but 40 and more than 50 per 100 000 for Black men and women, respectively. 4 Disparities in hypertension account for the greatest disparities in years of lost life compared with any other health condition. 6 A growing body of literature in different disciplines indicates that both social and environmental factors are important in the production and maintenance of hypertension disparities. 7–10 There are racial disparities in numerous social factors, such as socioeconomic status (SES), that have a robust association with hypertension. 2 For example, 2009 estimates put 26% of Blacks living in poverty compared with only 12% of Whites. 11 Importantly, however, controlling for poverty does not attenuate the racial disparities in hypertension, indicating that there are complex mechanisms at work. 12 There are also racial disparities in numerous environmental hazards, some of which are associated with hypertension. For example, lead is causally associated with a modest increase in blood pressure and risk of hypertension in a dose-dependent manner 13–16 through several biological mechanisms, including increases in oxidative stress and alterations in control of the cardiovascular system. 17 Furthermore, racial disparities in lead have been reported for decades. 18,19 In the environmental health literature, researchers have described the notion of differential vulnerability to the deleterious health effects of environmental hazards. 20,21 Some have shown that psychosocial stress and social stressors potentiate the association between lead and blood pressure. For example, in 1 study, men who report high levels of perceived stress show an association between bone lead and blood pressure, whereas men who do not report high levels of stress do not reveal this association. 22 Similarly, those adults who have higher allostatic load scores, a measure of stress-related wear and tear on the body, show a stronger association between blood lead and the odds of hypertension compared with adults with lower allostatic load scores. 23,24 It may be that this differential vulnerability, resulting from differential exposure to social factors, contributes to racial disparities in hypertension. 25 In other words, it may be that the greater social stressors and psychosocial stress experienced by Black compared with White Americans may exacerbate the health effects of environmental hazards, including lead. In fact, researchers have reported that there is a modifying effect of race on the association between blood lead and blood pressure. Specifically, Black adults exhibit a roughly 1 millimeter mercury increase in systolic blood pressure for every 3 micrograms increase in blood lead. 26 Yet, no such association is seen for Whites. 19,26,27 It may be that, compared with White adults, Black adults show a stronger association between lead and blood pressure because they experience greater social stressors, such as higher levels of poverty. In the present study, we have updated and expanded on previous work by examining the notion that social disadvantage, as marked by race and SES, modifies the association between blood lead and blood pressure. Specifically, we first updated the literature on the modifying effect of race on the association between blood lead and blood pressure. The most recent work in this area is based on data from 1988 to 1991. Blood lead levels have continued to decline for both Blacks and Whites. 19 Because there is a dose-dependent association between lead and blood pressure, it is not known whether blood lead and blood pressure are associated for Black adults using current data (2001 to 2008). Second, we examined the role of SES, specifically education and poverty, in the stronger association between blood lead and blood pressure seen in Black compared with White adults.
