In the United States, obesity and hypertension are more common in blacks than in whites, but that general statement hides some important sex differences. Thus, in black women the prevalences of both obesity and hypertension are greater than in white women, whereas in men, although there is no racial difference in obesity, in blacks hypertension is more common and more severe than in whites. For white people, there is a well-documented causal relationship between obesity and hypertension, however, results from the second National Health and Nutrition Examination (NHANES II) suggest that this relationship is not so strong for blacks. Obesity is also an important risk factor for diabetes, which in itelf is associated with hypertension. The mechanisms of obesity-associated hypertension appears to be an inadequate vasodilation in the face of the increased blood volume and cardiac output, which are the natural consequences of an increased body mass. This defect in control of vascular resistance has been attributed to increased activity of the sympathetic nervous system, abnormal reninangiotensin-aldosterone relationships, and insulin resistance. However, none of these attributes has been found to be the exclusive characteristic of obese hypertensive as compared with normotensive obese subjects.
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