(in addition to other mechanisms discussed below) can therefore have negative short-and long-term consequences for the brain.

When available studies to date are considered in aggregate, the relation of cardiovascular diseases to cognitive function has been one of the more extensively investigated of the research areas discussed above (Waldstein and Elias, in press; Waldstein et al., in press). Because hypertension is often one of the earliest manifestations of cardiovascular disease and can occur without substantial occult comorbidities, there is an opportunity to conduct tightly controlled investigations of hypertension and cognition. Perhaps for this reason, hypertension has been studied fairly intensively and thus is examined here as a pertinent illustration of health-cognition relations.

Hypertension

Hypertension—defined as a sustained systolic and diastolic blood pressure greater than or equal to 140 millimeters of mercury (mm Hg) and/or 90 mm Hg, respectively, as measured on at least two separate occasions (Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, 1997)—affects one in four adults in the United States, or 50 million individuals (American Heart Association, 1998). Approximately 90 to 95 percent of all cases involve essential hypertension, a term that refers to a sustained blood pressure elevation of unknown cause. However, the etiology of essential hypertension actually involves a complex interplay of genetic and environmental factors (Kaplan, 1998). Elevated blood pressure that is attributable to a known medical disorder is called secondary hypertension.

Risk factors for hypertension include a positive family history, older age, male gender (until age 55, after which prevalence rates are greater among women), black race, and numerous lifestyle and behavioral factors such as excess body weight, physical inactivity, dietary factors including high sodium and low potassium or calcium intake, excessive alcohol consumption, oral contraceptive use, various psychosocial factors, and stress-related cardiovascular reactivity (American Heart Association, 1998; Joint National Committee, 1997; Kaplan, 1998). Hypertension is a major risk factor for atherosclerosis, coronary heart disease, and stroke (Stamler, 1992).

Hypertension and Cognitive Function

The relation of hypertension to cognitive function has been studied for over 50 years (for reviews see M.F. Elias et al., in press; Elias and Robbins, 1991; Waldstein, 1995; Waldstein and Katzel, in press; Waldstein et al., 1991a). Results of numerous case-control and cross-sectional, population-based stud-



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