Hypertension is 50% more common in blacks than whites in the U.S., and accounts for 20% of adult deaths among blacks. The causes of this increased risk are not well understood. Epidemiologic research has focused principally on black:white comparisons, where social and biological factors are confounded. In this competitive renewal application, the investigators request support to continue a large-scale research project on the evolution of hypertension risk across the course of the African diaspora. In this research project, known as The International Collaborative Study on Hypertension in Blacks (ICSHIB), the investigators have examined 18,000 individuals in Africa (Nigeria, Cameroon, Zimbabwe), the Caribbean (Barbados, St. Lucia, Jamaica) the UK (Manchester), and the U.S. (Maywood, IL). Using a standardized protocol, the gradient in risk from very low levels in rural Africa to in high levels in metropolitan Chicago have been characterized. The sociocultural determinants of these patterns have also been extensively documented. While population differences in risk status have been clearly documented, mechanistic studies will be required to understand the etiologic process. In the next phase the investigators propose to examine in further detail the role of the two most potent hypertensive risk factors, namely dietary sodium and obesity. Randomized trials will be carried out in Nigeria, Jamaica and Chicago to determine the relative sodium sensitivity of these populations and the factors which condition the blood pressure response. Studies of the renin-angiotensin system (RAS) and renal sodium handling will allow comparisons of the causal mechanisms. In addition, body composition will be studied in a large sample of each of these three populations to determine the role of body fat vs. lean body mass. Hormone status (i.e., insulin, leptin will be examined to define physiologic mechanisms, and physical activity will be measured by objective methods (using stable isotopes) to assess the role of sedentarism as a contributor to the hypertension risk experienced by the obese. Existing cohorts will be followed to determine hypertension sequelae and to examine the trajectory of blood pressure change with age. While previous hypertension research has often been largely confined to single cultural setting, much remains to be learned from broad contrasts across environments. The availability of new epidemiologic tools, including genetic markers, has created new opportunities in descriptive epidemiology. Multiple interactions are likely to occur among environmental and genetic risk factors; a broad range of environmental contrasts among genetically related populations creates a powerful research design to study these interactions. The African diaspora creates a unique opportunity for these cross-cultural studies.
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