Our objective was to determine the independent associations of SES and race/ethnicity with global CHD risk and metabolic syndrome/diabetes prevalence in the US population. SES was strongly, inversely associated with global CHD risk in both men and women from all race/ethnicity groups, except in Foreign-born Mexican American men. SES was also strongly, inversely associated with metabolic risk in women from three of the four race/ethnicity groups and in Non-Hispanic White men. Stronger SES associations in women than in men have been previously reported (15
), consistent with stronger SES-obesity relationships in women (36
). Previous studies have also found that education and income gradients in health are weaker in African Americans than in Caucasian Americans (11
); however, SES, defined by combining education and income, showed strong CHD risk gradients in all four race/ethnicity groups. This inconsistency is likely the result of differential employment and income returns from education (15
), so that education or income on its own does not adequately capture social standing.
Some but not all of the SES associations with global CHD risk were explained by differences in health behaviors (physical activity and smoking) and central obesity. Other mediators of SES effects are likely to include neighborhood deprivation, access to medical care, and the physiological impact of daily stresses related to social position.
In contrast to the strong SES gradients with risks, race/ethnicity differences in risks were not consistent across SES and gender strata: Compared to Non-Hispanic Whites, global CHD risk was higher only
in upper-SES, US-born, Mexican American men
and middle-SES, Non-Hispanic Black women
, and lower
in foreign-born, Mexican American men and women. Diabetes prevalence was higher in minority groups, but only in some SES strata, and metabolic risk was actually lower
in middle-SES, foreign-born Mexican American women. Previous studies that have examined ethnic disparities after stratifying by SES have also found black-white differences in risks only in middle and high SES strata, but these studies did not separate men from women, and did not examine predicted global CHD risk (9
). Lower CHD risk in foreign-born Mexican Americans has been previously noted (29
), and it has been recognized that the Hispanic paradox is actually an immigrant health phenomenon, resulting from selection pressures in migration that favor healthy immigrants (29
), return emigration of sicker individuals (‘salmon bias’), and better lifestyle choices (41
). Foreign-born Mexican Americans indeed had the lowest rates of current smoking and central obesity, but the risk reduction did not diminish with controls for lifestyle, suggesting that lack of acculturation is not a major explanation for this phenomenon.
The consistency of SES-risk gradients across gender and race/ethnicity strata, relative to the inconsistency of race/ethnicity disparities in risk across SES strata, suggest that SES, rather than race/ethnicity, is the main driver of social disparities in cardiovascular risk in the US. Previous studies in some populations have also found that SES eclipses race/ethnicity as a predictor of risks (42
), and that SES explains much of the race/ethnicity disparities in health risks (43
This study has some limitations that need to be acknowledged. The possibility of false discovery as a result of multiple testing hampers our ability to infer real race/ethnicity differences in risk, since differences were seen only in some, not all, SES strata; this is less of a concern with SES gradients, which were consistent across race/ethnicity groups and gender, but is a real possibility for ethnic differences that were detected, since they were seen in only some, not all, SES and gender strata.. Secondly, just as SES-risk associations varied by race/ethnicity, the effects of health behaviors on risks may also differ by ethnicity and SES (45
), in which case, one cannot completely control for health behaviors by including them as covariates in the model. Also, abdominal obesity which was used as a surrogate for health behaviors related to diet and exercise, is also affected by family history and other factors, and so, control for health behaviors may not have been adequate. Finally, differential response by SES within race/ethnic groups could have biased our findings, although the use of weights designed to make the sample nationally representative should have diminished such bias.
The study’s limitations are outweighed by its strengths. In contrast to previous studies that have examined disparities in individual risk factors for CHD, we examined global risk for CHD. Disparities in individual risk factors can be in opposite directions (5
) and effects of risk factors can vary by gender; thus disparities in a global risk measure are more relevant to actual outcomes. A few studies have previously examined disparities in global CHD risk, but have either studied only one gender (13
) or not controlled for race/ethnicity (36
) or SES (46
). Since the predictive ability of the Framingham risk score may vary by SES and race/ethnicity (48
), we also examined ORs for prevalent CHD or CHD risk-equivalent (highest risk group), and the disparities were similar to those for predicted risk. Secondly, unlike other studies of ethnic disparities, we conducted SES-stratified analyses, the more appropriate way to control for SES when SES associations differ between groups. Third, we separated US-born from foreign-born Mexican Americans, since their social experiences are distinct, and we found important differences.
In conclusion, this large, national study documents strong, inverse SES gradients with CHD risk in all race/ethnicity groups, and demonstrates that race/ethnicity disparities in risk are primarily due to SES differences between the groups. Healthy lifestyle choices and avoidance of central obesity appear to dampen SES associations. Socioeconomically disadvantaged individuals need to be specifically targeted for early risk detection and management and health behavior counseling if we are to improve the cardiovascular health of the nation.