Consistent with previous work,1–4
the current study found that older black adults scored worse on cognitive function tests than age-comparable older white adults but that, after accounting for differences in demographic and socioeconomic characteristics, score differentials decreased markedly. Characteristics not commonly measured in studies of cognition and dementia, such as literacy and financial adequacy, in addition to age, sex, and education, were significantly associated with cognitive test scores and helped explain differences in scores between older black and white adults. The score differential diminished to a greater extent for the 3MS than the DSS test, possibly indicating that socioeconomic indicators affect deficits in cognitive domains such as memory and language more than attention and visual spatial abilities do.
The magnitude of the ethnicity-related disparity in cognitive performance in this study was comparable with previous studies of older black and white adults that found lower cognitive test scores for blacks on the Mini-Mental State Examination (MMSE), Short Portable Mental Status Questionnaire, Community Screening Interview for Dementia, and the Buschke Verbal Memory Test.2,3,8,21–23
Several studies have attributed such differences to differences in level and quality of education.9,24–27
Indeed, one study that included black and white participants with similar education levels reported similar cognitive test scores.28
More recently, a study on reading level and cognition in black participants found that reading was a significant predictor of cognitive scores independent of education, suggesting that quality of education may be associated with differences in cognitive performance.8,9
The current study suggests that literacy, a correlate of education and possibly a more accurate measure of reading abilities over a lifetime, is strongly associated with cognitive test performance and mediates some of the differences between cognitive scores between older black and white adults. The adjustment of socioeconomic indicators greatly reduced the difference between black participants and white participants in odds of low 3MS score, defined using a cutoff of 80 on the 3MS.
This study builds on prior work including a wide range of psychosocial, health-related, and socioeconomic characteristics. Few studies,7,27,29
have simultaneously evaluated socioeconomic and health-related differences as potential mediators of cognitive test score differentials across minority groups. The current findings clearly indicate that socioeconomic factors such as education, literacy, income, and financial adequacy not only have an independent association with cognitive performance, but also explain a substantial amount of the difference in cognitive testing between older blacks and whites. Socioeconomic factors explain much more of the difference than any of the health-related factors examined. Given that the 3MS and DSS and similar batteries are routinely used to evaluate the cognitive status of older adults and may often form the basis for clinical treatment and placement decisions, attention to non-health related factors that may affect performance on these tests is even more critical. In both blacks and whites, education, income, and disease are potentially modifiable, and lower scores should improve in both groups as these disparities are addressed over time.
studies of cognitive impairment typically find that blacks have higher rates than whites. Several studies of dementia or Alzheimer’s disease (AD) have attempted to discern whether the differences in disease rates are due to genetic or environmental causes. Most of these studies have used the MMSE to screen individuals and followed-up the screen with a clinical evaluation of dementia. Some studies suggest that the apolipoprotein E epsilon 4 (ApoE-ε4) allele is not as robust a risk factor in older black and Latino adults as it is in older white adults,33
but other studies report similar rates of dementia by ApoE-ε4 status in primarily white34
and primarily black groups. A cross-cultural study performed in Nigeria and Indiana found that the incidence of dementia and AD was nearly three times higher in blacks from Indiana as from Nigeria. The authors speculated that high rates of vascular risk factors in Indiana, as well as differences in the association between ApoE-ε4 and AD, may explain the differential incidence rates, not differences in SES or literacy.35
Perhaps the issues of social standing and perceived poverty relative to other groups are as important as actual SES measures,36
thus explaining why SES per se did not predict greater AD incidence in Nigeria than in the United States. Consequently, the current findings—namely that low literacy is associated with poor cognitive function—must be viewed in the context of relative affluence of the United States compared with other countries.
Potential hypotheses regarding the effect of education on dementia37
can be extended to help explain why, in this study, socioeconomic indicators such as education and literacy accounted for most of the ethnoracial variation in cognitive function test scores. The first hypothesis is the selective hypothesis: people who function poorly on cognitive function tests have diminished cognitive reserve from early childhood. The second hypothesis is an associational hypothesis: poor education correlates with other potential mechanisms such as poor nutrition, alcohol abuse, and inadequate health care; these other mechanisms account for why minority older adults score lower on cognitive function tests. The third hypothesis is the educational hypothesis: lifelong education builds a cognitive reserve that could compensate for brain deterioration. Because the current findings suggest that education and literacy are potent predictors of the race/ethnic disparity in cognitive function test scores after controlling for many known confounders including comorbidities and alcohol, the educational hypothesis is the most likely.
Some potential limitations of this study deserve comment. Although adjustments were made for many potential mediators of cognitive performance that differed between blacks and whites, a few key confounders were missing. For example, there exists some evidence that lifetime stress negatively and occupational attainment positively influence cognition, but these factors were not measured here.38
Second, because this study is cross-sectional in design, one cannot determine whether factors associated with cognitive performance would also be associated with cognitive decline. Future studies will examine the role of these factors in cognitive change over time within this cohort. Finally, this study addresses cognitive test score differences between older black and white adults; further study is needed to address the relationship between ethnicity and cognition in ethnic groups other than black and white. In addition, further investigation is needed in people of varied socioeconomic status.
This study suggests that black participants had lower unadjusted cognitive function scores than white participants, but after adjustment for socioeconomic factors and other variables, the difference in scores between blacks and whites decreased substantially. In addition, characteristics not commonly measured in cognitive studies, such as literacy and financial adequacy, were found to be important predictors of cognitive scores. Specifically, tests that can assess scholastic aptitude in early life may be important in separating the effects of literacy, premorbid intelligence, and education on cognitive function test scores in diverse older adult groups. Future studies with detailed examination of literacy, scholastic aptitude, financial adequacy, and other socioeconomic factors over the life course are needed to investigate the mechanisms by which these factors affect cognitive test differences. In addition, further studies are needed to examine whether these same socioeconomic factors may help explain differences in rates of cognitive impairment or AD in people with or without genetic risk factors.