Disparities in Cognitive Functioning by Race/Ethnicity in the Baltimore Memory Study

Brian S. Schwartz; Thomas A. Glass; Karen I. Bolla; Walter F. Stewart; Gregory Glass; Meghan Rasmussen; Joseph Bressler; Weiping Shi; Karen Bandeen-Roche

Disclosures

Environ Health Perspect. 2004;112(3) 

In This Article

Abstract and Introduction

The Baltimore Memory Study is a cohort study of the multilevel determinants of cognitive decline in 50-70-year-old randomly selected residents of specific city neighborhoods. Prior studies have demonstrated that cognitive function differs by race/ethnicity, with lower scores in minorities than in whites, but the underlying basis for these differences is not understood. Studies have differed in the rigor with which they evaluated and controlled for such important confounding variables as socioeconomic status (SES), health-related behaviors, comorbid illnesses, and factors in the physical environment. The goal of this study was to describe differences in neurobehavioral test scores by race/ethnicity, before and after control for a four-dimensional measure of SES and health-related behaviors and health conditions, in a cross-sectional analysis of first visit data. Random samples of households in the study area were selected until enrollment goals were reached. Among the 2,351 persons on whom eligibility was determined, 60.8% were scheduled for an enrollment visit; of these, 1,140 (81.3%) were enrolled and tested. These study participants were 34.3% male and 65.7% female and were from 65 Baltimore, Maryland, neighborhoods. After adjustment for age, sex, and testing technician, there were large and statistically significant differences in neurobehavioral test scores by race/ethnicity, with African-American scores lower than those for whites, for both men and women. After adjustment for individual SES (educational status, household income, household assets, and occupational status), the average difference declined by 25.8%. After additional adjustment for SES, health-related behaviors and health conditions, and blood lead, the average difference declined another 10%, but large differences persisted; African Americans had test scores that averaged 0.43 standard deviation lower than those for whites across all neurobehavioral tests. These differences were present in all cognitive domains, including tests that would not be characterized as susceptible to differential item functioning by race/ethnicity, suggesting that the results are not due to race/ethnicity-associated measurement error.

The impending retirement of the baby-boom cohort, along with geometric growth in the relative size of the older population, will dramatically alter the public health challenges of the 21st century. Demographics ensure that the numbers of persons with dementia and cognitive decline will increase in the coming decades (Brookmeyer et al. 1998). The determinants of cognitive dysfunction with increasing age are complex, multifactorial, and synergistic, involving features of the physical and social environments, as well as endogenous biologic (e.g., genetic) and behavioral factors. Although results are not entirely consistent (e.g., Munoz et al. 2000), there is substantial evidence that neurobehavioral test scores, cognitive decline over time, and dementia risk vary substantially by race/ethnicity (Fillenbaum et al. 1998; Graham et al. 1998; Gurland and Katz 1997; Gurland et al. 1999; Hall et al. 2000; Launer et al. 1999; Perkins et al. 1997; Shadlen et al. 1999; Stern et al. 1994; Wiederholt et al. 1993). The underlying basis for these differences has not been clearly delineated. Potential explanations include uncontrolled confounding by socioeconomic status (SES), comorbid illnesses that could influence cognitive function (e.g., cardiovascular disease), and chronic stress associated with race/ethnicity that is not fully captured by traditional measures of race/ethnicity, SES, or other indicators of the social environment. Previous studies have a number of limitations, including populations that are too old, samples that are not representative of underlying target populations, and incomplete control for important confounding variables, especially SES.

In considering the role of the social environment, neighborhood-level (or contextual) factors must be distinguished from individual-level (or compositional) factors, and these have in fact been separate foci of interest in earlier studies (Diez Roux 2001; Glass and Balfour 2003; Macintyre et al. 2002). Individual-level social variables that have been considered generally include those subsumed under the category of SES, which consists of such attributes as education, occupation, income, and wealth, but no prior studies have rigorously controlled for this set of measures. Although the evidence is compelling that individual SES is associated with cognitive function in late life, the pathways through which this association operates have yet to be elucidated.

Population-specific differences in the presence of disease, health outcomes, or access to health care have been termed health disparities, and understanding the causes of these disparities and eliminating them is a primary goal of the Health Resources and Services Administration, the National Institutes of Health, and other American public health and research agencies (e.g., U.S. Department of Health and Human Services 2000). The National Institute of Environmental Health Sciences [National Institutes of Health (NIH), Department of Health and Human Services] has an active research program designed to disentangle the roles that the natural, built, and social environments play in disease causation. Here we report on the Baltimore Memory Study, which is funded under the trans-NIH research program. We present the detailed methods of the study, describe the disparities in neurobehavioral test scores in a large community sample of 50-70-year-old individuals from selected neighborhoods in Baltimore, Maryland, and evaluate selected individual-level social, physical environmental, and behavioral factors that account partially for these racial/ethnic differences in test scores. This work represents a case study in multilevel, multidisciplinary research, aimed at integrating knowledge within and across biologic, environmental, social, behavioral, and mathematical sciences.

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