tion. In this regard, Haan et al. (1999) found that individuals with carotid atherosclerosis, peripheral vascular disease, or diabetes mellitus, in addition to an APOE-ε4 allele, experienced a significantly greater rate of cognitive decline than individuals without an APOE-ε4 allele and or cardiovascular disease.

Neurotoxicity

Environmental or occupational exposure to chemicals, such as solvents and lead, exerts direct neurotoxic effects on the brain and is associated with diminished cognitive functioning (Hartmann, 1995; Morrow et al., in press). Both peak exposures and chronic low-level exposures are of concern. Individuals of lower socioeconomic status may be more likely to experience neurotoxic exposures.

Systemic Diseases

Numerous systemic diseases have been associated with poorer cognitive functioning. Examples include cardiovascular diseases, such as hypertension and myocardial infarction (Waldstein and Elias, in press; Waldstein et al., in press); pulmonary diseases, such as chronic obstructive pulmonary disease and asthma (Fitzpatrick et al., 1991; Hopkins and Bigler, in press; Grant et al., 1987; Prigatano et al., 1983); pancreatic diseases, such as diabetes mellitus (Reaven et al., 1990; Ryan, in press; Ryan et al., 1993); hepatic diseases, such as cirrhosis (Moss et al., 1995; Tarter and Van Thiel, in press); renal diseases (Hart et al., 1983; Pliskin et al., in press); autoimmune diseases, such as systemic lupus erythematosus (Beers, in press; Glanz et al., 1997); various cancers (Berg, 1988); sleep disorders, such as obstructive sleep apnea syndrome (Bédard et al., 1993; Kelly and Coppel, in press); and the human immunodeficiency virus and AIDS (Heaton et al., 1995; Kelly et al., 1996).

Disparities in health status among racial and ethnic minority groups and individuals of lower socioeconomic status or educational attainment are well documented (Haan and Kaplan, 1985; Haan et al., 1989; Kaplan and Keil, 1993). It is therefore possible that comorbidities may, in part, explain prior relations of race/ethnicity (e.g., for black Americans), lower education, and low socioeconomic status to poorer performance on cognitive tests. Health status should therefore be controlled in such investigations (Whitfield et al., 2000).

Medical and Surgical Treatments

A variety of medical and surgical treatments for disease have been shown to impact cognitive performance. Improvements, decrements, and absence



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