The association of skin color with blood pressure in US blacks with low socioeconomic status.

To determine the association of skin color, measured by a reflectometer, with blood pressure in US blacks, we studied a community sample of 457 blacks from three US cities. Persons taking antihypertensive medications were excluded. Both systolic and diastolic blood pressure were higher in darker persons and increased by 2 mm Hg for every 1-SD increase in skin darkness. However, the association was dependent on socioeconomic status, whether measured by education or an index consisting of education, occupation, and ethnicity, being present only in person with lower levels of either indicator. Using multiple linear regression, both systolic and diastolic blood pressure remained significantly associated with darker skin color in the lower levels of socioeconomic status, independent of age, body mass index, and concentrations of blood glucose, serum urea nitrogen, serum uric acid, and urinary sodium and potassium. The association of skin color with blood pressure only in low socioeconomic strata may be due to the lesser ability of such groups to deal with the psychosocial stress associated with darker skin color. However, these findings also are consistent with an interaction between an environmental factor associated with low socioeconomic status and a susceptible gene that has a higher prevalence in persons with darker skin color.