Relationship Between Skin Color and Blood Pressure in Egyptian Adults

Abstract

Abstract-In many, but not all societies, dark skin color is associated with high blood pressure. Whether the association between skin color and blood pressure is independent of known determinants of blood pressure remains controversial. We examined the association between skin color and blood pressure in 835 Egyptian adults (370 men and 465 women) participating in the National Hypertension Project, a national survey of hypertension prevalence and blood pressurerelated complications conducted in Egypt during 1991-1993. Skin color was assessed by measuring the concentration of cutaneous melanin in an unexposed area with the use of reflectance spectrophotometry. Higher concentrations of melanin were associated with lower body mass index, less education, manual labor (among men), and a lower urinary sodium-to-potassium ratio (among women). In multivariate regression analyses adjusted for age, body mass index, and education, there was a significant nonlinear association between blood pressure and skin color among women; in the lower to intermediate range of skin pigmentation, both systolic and diastolic blood pressures were higher in women with greater concentrations of cutaneous melanin. In men, blood pressure was not associated with skin color. When we used a subjective assessment of skin color, there was no significant difference in blood pressure between black-skinned Egyptians (predominantly of Nubian descent) and fair-skinned Egyptians for either gender. While the significant relationship in women appeared to be independent of known risk factors for hypertension, residual confounding may explain the association. (Hypertension. 2000;36:296-302.)

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“…These findings cast doubt on previous suggestions that skin color reflects genetic susceptibility to high blood pressure (Boyle, 1970;Gleiberman et al, 1999) or that skin color and blood pressure are linked physiologically (Harburg et al, 1978;Mosley et al, 2000). Both the genetic and the physiologic hypotheses predict a positive association between skin pigmentation and blood pressure.…”

“…None of these studies reported an association between pigmentation and blood pressure across the entire sample, after controlling for age, sex, and socioeconomic status. Klag et al (1991) found an association only in the lowest socioeconomic group, while Mosley et al (2000) reported an association only in Egyptian women. By contrast, the only studies that observed a consistent association between skin color and blood pressure across the sample measured skin color with some form of observer rating (Costas et al, 1981;Gleiberman et al, 1995;Harburg et al, 1973Harburg et al, , 1978Sichieri et al, 2001).…”

“…Once we recognize that distinction, however, previous studies of the skin color-blood pressure relationship provide additional support for the stress hypothesis as the most plausible alternative. Of the 13 previous studies of this relationship, only six measured skin pigmentation with reflectance spectrophotometry (Boyle, 1970;Ernst et al, 1997;Keil et al, 1977Keil et al, , 1981Klag et al, 1991;Mosley et al, 2000). None of these studies reported an association between pigmentation and blood pressure across the entire sample, after controlling for age, sex, and socioeconomic status.…”

“…Some researchers propose that dark skin color, as a marker of African admixture, is linked to a genetic predisposition for hypertension (Boyle, 1970;Gleiberman et al, 1999). Others speculate that dark skin color and high blood pressure are linked by an endocrine pathway involved in both melanin production and blood pressure control (Harburg et al, 1978;Mosley et al, 2000). Still others suggest that dark skin color, as a marker of subordinate social status in racially stratified societies, increases exposure to psychosocial stress associated with racism and social inequality (Dressler, 1991;Tyroler and James, 1978).…”

“…These conceptually distinct variables require distinct measurement operations. Yet all previous studies of the skin color-blood pressure relationship operationalize skin color implicitly in terms of skin pigmentation, as measured by reflectance spectrophotometry (Boyle, 1970;Ernst et al, 1997;Keil et al, 1977Keil et al, , 1981Klag et al, 1991;Mosley et al, 2000), by observer ratings (Dressler, 1991;Dressler et al, 1999;Gleiberman et al, 1995;Harburg et al, 1973Harburg et al, , 1978Mosley et al, 2000;Sichieri et al, 2001), or by comparison to standardized color chips (Costas et al, 1981).…”