Red Cell Distribution Width Is Directly Associated with Poor Cognitive Performance among Nonanemic, Middle-Aged, Urban Adults

Abstract

Background: Epidemiological evidence suggests that both anemia and elevated red cell distribution width (RDW) are associated with cognitive impairment. However, the interplay between these 2 predictors has been understudied. Objectives: We examined sex- and anemia-specific associations between RDW and cognitive performance among urban adults in the United States. Methods: Data from the Healthy Aging in Neighborhoods of Diversity Across the Life Span Study (Baltimore, MD; participants aged 30-65 y at baseline, ∼59% African-American, 45% men) were used. Participants were selected based on the completion of 11 cognitive tasks at baseline (2004-2009) and follow-up (2009-2013) visits (mean time between visits: 4.64 ± 0.93 y) and availability of exposure and covariate data, yielding a sample of between 1526 and 1646 adults out of the initial 3720 adults recruited at baseline. Multiple linear mixed-effects regression models were conducted with RDW as the main exposure of interest and anemia/sex as the key effect modifiers. Results: Overall, high RDWs were linked to poorer baseline performance on the California Verbal Learning Test (CVLT) List A (per 1 unit increase in RDW %, main effect: γ01 = -0.369 ± 0.114; P = 0.001) and to slower rates of decline on the CVLT Delayed Free Recall (per 1 unit increase in RDW %, RDW × time: γ11 = +0.036 ± 0.013; P = 0.007). Among nonanemic participants, RDWs were consistently associated with poorer baseline performance on the Trailmaking Test, Part A (γ01 = +3.11 ± 0.89; P < 0.001) and on the CVLT List A (γ01 = -0.560 ± 0.158; P < 0.001). Moreover, RDWs were associated with poorer baseline performance on the Brief Test of Attention in the total population (γ01 = -0.123 ± 0.039; P = 0.001) and among men (γ01 = -0.221 ± 0.068; P = 0.001). We did not detect an association between hemoglobin (Hb) and baseline cognitive performance or changes over time. Conclusions: Elevated RDW had a consistent cross-sectional association with poor cognitive performance in the domains of verbal memory and attention among the nonanemic group in a sample of middle-aged, urban adults. Anemia and Hb concentrations were not associated with cognition. More longitudinal studies are needed to replicate our findings.