Abstract
Objectives: Despite our knowledge on the effect of cognitive test score on subsequent risk of mortality, few studies have compared Blacks and Whites for this association. The current study was conducted on Black-White differences in the magnitude of the association between baseline cognitive test score and all-cause mortality in a nationally representative sample of adults in the United States over 25 years. 
 Methods: We used data of the Americans’ Changing Lives Study (ACL), 1986 – 2011, a national prospective cohort in U.S. The study followed 3,361 adults (2,205 White and 1,156 Blacks), age 25 and older, for up to 25 years. The independent variable was cognitive test score measured at baseline (1986) using the 4-item version of the Short Portable Mental Status Questionnaire, treated in two different ways (as a dichotomous and as a continuous variable). The dependent variable was time to death (due to all causes) during the follow up period. Covariates included baseline age, gender, education, income, number of chronic diseases, self-rated health, and depressive symptoms. Race (Black versus White) was the focal effect modifier. We used a series of Cox proportional hazards models in the total sample, and by race, in the absence and presence of health variables. 
 Results: Overall, cognitive test score predicted mortality risk. A significant interaction was found between race and baseline cognitive test score suggesting that baseline cognitive test score has a weaker protective effect against all-cause mortality for Blacks in comparison to Whites. In race-stratified models, cognitive test score at baseline predicted risk of all-cause mortality for Whites but not Blacks, in the absence and presence of baseline socio-economic and health variables. The results were similar regardless of how we treated baseline cognitive test score. 
 Conclusions: In the United States, baseline cognitive test score has a weaker protective effect against all-cause mortality over a long period of time for Blacks than Whites. The finding is in line with the Minorities Diminished Returns theory and is probably due to structural and interpersonal racism.
Highlights
It is well established that particular cognitive abilities decline with aging[1] and this decline is associated with morbidity[2] and mortality.[3]
On the main aim of the study, major Black- White differences were found in the predictive role of baseline cognitive function on long-term mortality
The study showed lower cognitive function at baseline for Blacks, and Black and White similarities in role of age and socio-economic status on cognitive function. These findings contribute to the existing literature on health disparities in the United States, as stated by Moody-Ayers and colleagues in 2005, “efforts to understand cognitive function may enhance our understanding of Black - White disparities in health outcomes.”[11]
Summary
It is well established that particular cognitive abilities decline with aging[1] and this decline is associated with morbidity[2] and mortality.[3]. Despite the well-defined link between baseline cognitive function and subsequent all-cause mortality,[3,79] it is not known whether or not diverse population groups differ in this relationship, as very few studies have ever tested predictive ability of cognitive limitation on long term mortality among racial and ethnic minority populations. Of the few studies that have been conducted among racial and ethnic minorities, most have enrolled Hispanics.[6,10] In a study among older Mexican Americans, baseline and 2-year decline in cognitive functioning independently predicted risk of all-cause mortality.[6] In another study among Mexican Americans, frailty and cognitive test score were risk factors for mortality separately, the effect of cognitive impairment on mortality disappeared by controlling for frailty.[10] compared to Whites or even Hispanics, less is known about this association among Black Americans.[11]
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