摘要：Objectives. We tested competing hypotheses for the skin color–blood pressure relationship by analyzing the association between blood pressure and 2 skin color variables: skin pigmentation and social classification. Methods. We measured skin pigmentation by reflectance spectrophotometry and social classification by linking respondents to ethnographic data on the cultural model of “color” in southeastern Puerto Rico. We used multiple regression analysis to test the associations between these variables and blood pressure in a community-based sample of Puerto Rican adults aged 25–55 years (n=100). Regression models included age, gender, body mass index (BMI), self-reported use of antihypertensive medication, and socioeconomic status (SES). Results. Social classification, but not skin pigmentation, is associated with systolic and diastolic blood pressure through a statistical interaction with SES, independent of age, gender, BMI, self-reported use of antihypertensive medication, and skin reflectance. Conclusion. Our findings suggest that sociocultural processes mediate the relationship between skin color and blood pressure. They also help to clarify the meaning and measurement of skin color and “race” as social variables in health research. Throughout the Americas, people of African ancestry have higher mean blood pressures and higher rates of hypertension than do others in the same societies. This pattern was first observed in the United States in 1932. 1 Over 70 years later, excess hypertension still contributes more to the diminished life expectancy of African Americans than does any other major cause of death, including cancer, diabetes, stroke, or HIV/AIDS. 2 Although the prevalence of hypertension and the magnitude of inequalities vary by country, a general pattern of elevated blood pressure holds elsewhere in the African Diaspora. 3 – 7 There remains no consensus as to why this pattern exists, leading some to call it “the puzzle of hypertension in African-Americans.” 8 One key piece of the puzzle is that, within populations of African ancestry, darker-skinned individuals tend to have higher mean blood pressures than do their lighter-skinned counterparts. Previous researchers have proposed 2 major explanations for this relationship. The first is that dark skin color, as a marker of African ancestry, is linked to a genetic predisposition for high blood pressure. 9 , 10 The second is that dark skin color, as a marker of subordinate social status, exposes dark-skinned individuals to racial discrimination, poverty, and other stressors related to blood pressure. 11 – 13 These competing hypotheses—1 genetic, 1 sociocultural—encapsulate the debate over race and health in general, making the skin color–blood pressure relationship a convenient microcosm of the broader problem. Our purpose was to test competing explanations for the relationship between skin color and blood pressure more directly than has been done before. We address an important limitation of previous studies by recognizing that genetic and sociocultural hypotheses refer to distinct dimensions of skin color. The hypothesis that skin color is linked to a genetic predisposition for high blood pressure refers to the phenotype of skin pigmentation. The hypothesis that skin color is a marker of exposure to social stressors refers to the cultural significance of skin color as a criterion of social classification. These conceptually distinct variables require distinct measurement operations. However, previous studies have not aimed to isolate the cultural and biological dimensions of skin color or to test their associations with blood pressure. Measuring the biological dimension of skin color is straightforward in principle. Reflectance spectrophotometry provides an objective measurement of skin pigmentation attributable to melanin, the implicit skin color variable in genetic hypotheses for the skin color–blood pressure relationship. The key measurement challenges involve the choice of instrument and use of proper technique. 14 , 15 Measuring the cultural dimension of skin color presents a different set of challenges. It first requires a test of the assumption that there is a shared cultural model that assigns meaning to skin color variation. It then requires a way to estimate how the color status of any given individual would be defined according to that model. In short, it requires treating the notion that race is a cultural construct as an empirical matter, not a mantra. We use data from a preliminary study in Puerto Rico to test the hypothesis that blood pressure is associated with the cultural rather than biological significance of skin color. Two factors make Puerto Rico an appropriate setting. First, an earlier study reported an association between skin pigmentation and systolic blood pressure (SBP) among 4000 urban men, but it did not address the extent to which this association reflected genetic or sociocultural mechanisms. 16 Second, previous ethnography 17 – 19 indicates that the local cultural model of color (ko-lór) differs from the American model of race in important ways. In particular, color classification is shaped not only by skin color but also by other physical features and, possibly, by social status markers like wealth, family background, or residential area. One consequence is that, for a given level of skin pigmentation, there should be variability in social classification, making it possible to measure the cultural and biological dimensions of skin color as distinct variables.
