The Moderating Role of Race and Ethnicity in the Association Between Cognitive Performance and Functional Abilities in Later Life

INTRODUCTION

There is consistent evidence that cognitive impairment in Alzheimer’s disease and related dementias (ADRD) is associated with functional limitations among older adults [1]. Overall, individuals with some degrees of impairment in different cognitive domains including executive functioning (often measured by Digit Symbol Substitution Test) have difficulties in key components of daily activities and making everyday life decisions [2–4]. Historically underrepresented groups in the U.S. such as African Americans and Hispanics are greater at-risk for developing later life disability and dependence [1, 5] which may be associated with their higher likelihood of ADRD compared to the White populations [6]. Nevertheless, the complexity of the interrelationships between cognition, functional ability, and race/ethnicity, has not been well studied from the perspective of ethnoracial intersectionality. Race and ethnicity are self-identified social constructs; however, health research to date has often misrepresented them as the biological basis of many diseases and health outcomes [7]. This phenomenon has disregarded the need to explore systemic inequities in social determinants [7] driving potential differences in cognitive health status, dementia burden and consequences across race/ethnicity groups [8, 9]. In 2015, the National Institute of Aging (NIA) established a framework for describing factors/social determinants of health disparities at different levels (e.g., environmental, sociocultural, behavioral, and biological) that considers race/ethnicity as a fundamental factor [8]. This framework recommends examining the mechanisms by which these factors interact at different levels to influence ethnoracial disparities in dementia.

In 2021, a study that aimed to explore ethnoracial differences in the association between instrumental activities of daily living and cognition found no significant differences [4]. However, in 2022, other findings demonstrated positive associations between two physical function measures, grip strength and gait speed, and cognition across race/ethnicity, while revealing a significant difference among the Black and Latino groups in the association between gait speed and executive function [10]. These findings warrant further inquiry to elucidate the extent to which underrepresented race/ethnic status, such as African American or Hispanic, impacts the aging process, as well as understanding the role of ethnoracial differences in the relationship between cognition and functional ability. With this goal in mind, our study examined the association between low cognitive performance and functional limitations while exploring the moderating effect of race/ethnicity in this association.

METHODS

RESULTS

Table 1 shows the differences in demographic characteristics, cognitive performance, and functional domains overall and across race/ethnicity. Hispanic and NHB participants were younger, more obese and tended to have less than high school education and relatively lower socioeconomic status compared to the NHW participants. A greater proportion of Hispanics and NHBs had ADL difficulties compared to NHWs. Approximately 39% of Hispanics and 31% of NHBs had low DSST scores compared to 13.37% of NHWs.

In the crude analyses, significant associations were revealed between low DSST scores and limitations for all functional domains. Table 2 displays results from the adjusted logistic regression analyzing associations between low DSST score and each domain of functional limitations and moderation effects of race/ethnicity in these associations. The participants with low DSST scores had 2.45 (CI 1.64–3.67) greater odds for ADL difficulties; 2.73 for IADL difficulties (CI 1.77–4.20); and 2.53 for LSA difficulties (CI 1.79–3.57) compared to those who did not have low DSST scores when adjusted for all covariates (Table 2). Results from the moderation analysis indicated that these main effects were qualified by significant interactions between each race/ethnicity variable and low DSST score (Hispanic*Low DSST; NHB*Low DSST) (Table 2). Compared to the NHWs, Hispanics with low DSST score were found to be less likely to exhibit limitations in ADL (OR 0.33, CI 0.23–0.46), IADL (OR 0.28, CI 0.20–0.39), and LSA (OR 0.35, CI 0.26–0.48) domains. Similarly, NHBs with low DSST score were less likely to exhibit limitations in ADL (OR 0.40, CI 0.29–0.54), IADL (OR 0.29, CI 0.22–0.40), and LSA (OR 0.38, CI 0.26–0.54) domains.

In the stratified models, the association between low cognitive performance and functional limitations remained significant for the NHWs in ADL, IADL, and LSA domains (OR 2.91, 3.69, 3.21, respectively), became attenuated for the NHBs (OR 1.76, 1.63, 1.80, respectively), and non-significant for the Hispanics (OR 1.42, 0.90, 1.05, respectively) (Fig. 1 and Supplementary Table 1). This subgroup analysis supports our results in moderation analysis and indicates that the associations are different across the racial/ethnic groups. Additionally, the stratified results did not differ by sex in respective race/ethnicity except for NHB females which became non-significant.

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Fig. 1

Predicted Probabilities of Functional Limitations among Hispanics, Non-Hispanic Blacks (NHB), and Non-Hispanic Whites (NHW).

DISCUSSION

This research indicates that low cognitive performance is significantly associated with functional limitations in several domains among the U.S. older adults. However, being Hispanic and Black may weaken this association, thus, exerting a protective effect. Our results align with the existing evidence describing the link between cognitive performance and functional abilities which may differ by race/ethnicity [1, 16]. A study by Kuo and colleagues demonstrated an association between poorer DSST scores and later life disability in several functional domains using the NHANES 1999–2002 data [2]. Our findings are further supported by George and colleagues suggesting associations between stronger grip strength and faster gait speed with better cognition in multiple domains across race/ethnicity [10]. Like our results, their analysis also revealed a significant racial/ethnic difference in the relationship of gait speed with executive function which became weakened for the Black participants and non-significant for the Latinos compared to the Whites and Asians.

The negative moderating effect of NHBs and Hispanics on the association between low cognitive performance and functional limitations revealed in our study, may have been influenced by the age or age-related factors. Older adults from NHB and Hispanic groups were younger than the NHWs, although this could not be addressed in our analysis as the DSST does not have any age-specific cut-off points. Furthermore, the functional limitations were self-reported, and perceptions of the intensity/level of difficulties may vary across different races/ethnicities or culture. Current research, including this study, fails to capture cultural understandings of physical functionality as most of the existing measures have not been culturally validated [17]. An assessment of functional limitation that involves culturally adapted objective measures is needed to explain the cross-cultural differences as well as to mitigate self-reporting bias. The protective effect of Hispanic and NHB race/ethnicity on the development of functional limitations among people with low cognitive performance in specific domains, however, may be explained by the protective factor model of resiliency [18]. This model demonstrates the moderating effect of protective factors and how they interact with specific risk factors to mitigate negative health consequences [18–21]. Racial centrality, the degree to which an individual perceives his/her racial identity [22] possesses protective properties [16]. Individuals with high racial centrality are more likely to be resilient due to experiencing more racial discrimination and can develop effective coping strategies that may extend to functional difficulties [18, 23]. The NIA health disparities framework describes specific psychological capacities, individual attitudes, and utilizations of social support as the resilience factors that contribute to coping mechanisms when exposed to perceived psychosocial stressors [8, 24–26]. Practicing some behaviors including physical, spiritual, or social activities regulate these resilience factors in response to negative environmental and sociocultural experiences [24, 27] such as limited healthcare access due to different cultural beliefs and languages, discrimination, immigration status, and other societal challenges among the underrepresented racial/ethnic groups in the U.S. [8, 9]. On the other hand, tobacco use, alcohol consumption, poor diet quality etc. are some negative health behaviors adopted as coping strategies that adversely impact quality of life over the course of time [28].

The findings of this study shed light on the potential resilience of Hispanic and NHB participants with low cognitive performance when compared with similarly challenged Whites with respect to functional limitations. The moderating effect of Hispanic and Black race/ethnicity in the association of low cognitive performance and functional limitations found in this study has clinical implications for dementia and cognitive health disparity and warrants further inquiry. Qualitative investigations of personal, sociocultural, or environmental factors (e.g., perceived racial bias, perceived racial discrimination, racial identity) associated with biopsychosocial models of functionality among historically underrepresented groups with poorer cognitive performance or cognitive impairment may clarify the contributions of these factors in this pathway. Moreover, a prospective design should be considered in future research as the cross-sectional nature of the NHANES data does not assess temporality or causal associations between the studyvariables.