Life‐space mobility and cognitive function: The REasons for geographic and racial differences in stroke (REGARDS) study

Understanding the relationship between community mobility and cognition can guide medical care and support for individuals in greatest need. Better mobility is associated with better cognitive function, but Black individuals, who have higher risk of mobility problems and cognitive impairment compared to White individuals, have been underrepresented in prior studies.1 Because higher atherosclerotic cardiovascular disease (ASCVD) risk is associated with both mobility limitations and cognitive decline, we hypothesized that associations between mobility and cognition would be stronger among individuals with history of or at high risk of ASCVD.2, 3 We, therefore, examined the association between life-space mobility and cognitive function and whether this association varied by ASCVD risk and race. We conducted a cross-sectional analysis of participants from the longitudinal REasons for Geographic and Racial Differences in Stroke (REGARDS) Study which recruited 30,239 community-dwelling Black and White adults aged ≥45 years from the 48 continental United States in 2003–2007.4 We included 7016 participants without history of stroke who completed a 90-s Digit Symbol Substitution Test (DSST) and Life-Space Assessment (LSA) in 2013–2016. DSST, a Wechsler Adult Intelligence Scale subtest, was used in REGARDS because of its sensitivity to age-related changes in cognition and cognitive dysfunction across the age range.5, 6 DSST scores are influenced by processing speed, working memory, learning, executive function, and motor control.5 LSA, a composite measure of self-reported community mobility, was based on self-reported distance and frequency a person has moved in the past 4 weeks and need of assistance from equipment or another person.7 The minimal important change in LSA composite score is 5 points.8 We used linear regression to model the association between a 5-point difference in LSA and DSST. We examined potential interaction with race and ASCVD risk, estimated using a history of coronary heart disease and Pooled Cohort Risk Equations which include information on age, sex, race, total cholesterol, high density lipoprotein cholesterol, antihypertensive therapy, systolic blood pressure, cigarette smoking, and diabetes.9 Four categories of ASCVD risk were created based on history of CHD and 10-year predicted risk of ASCVD among those without CHD: low risk (<10%), medium risk (10%–20%), high risk (>20%). Models were adjusted for age, sex, race, income, education level, region of residence, Short Form-12 mental and physical component summary scores, exercise, depressive symptoms, perceived stress, social support, relationship status, difficulty traveling by vehicle, ASCVD risk, diabetes, and hypertension. Because the prevalence of mobility problems and cognitive impairment increase with age, we repeated analyses among participants aged ≥65 years (n = 5741) and ≥75 years (n = 2493). Analyses were conducted using SAS version 9.4 (Cary, NC). p-values <0.05 were considered statistically significant. The mean age of the population was 71.6 years (range 52–97 years), 29.2% of participants were Black, and 56.9% were women (Table 1). Mean LSA composite score was 82.4 (max 120), and mean DSST was 38.7 (max 133). A 5-point higher LSA composite score was associated with a 0.16-point higher DSST score (95% CI 0.11–0.21) after adjusting for potential confounders (Figure 1). The association was strongest in the low ASCVD risk group (0.22, 95% CI 0.10–0.33) and in White participants (0.18, 95% CI 0.11–0.24), though differences in associations by ASCVD risk (p-interaction = 0.08) and race (p-interaction = 0.09) were not statistically significant. Results were similar when analyses were limited to participants aged ≥65 years and ≥75 years. In this large cross-sectional study of Black and White adults age ≥52 years, community mobility measured using LSA was significantly associated with cognitive function measured by DSST. However, the association (0.16-point higher DSST associated with 5-point higher LSA) was very small when compared to the minimal important DSST difference, reported to be 3–5 points.10 Contrary to our hypothesis, the association was strongest in the low-risk ASCVD group. Because ASCVD and ASCVD risk factors are major determinants of cognitive function, the influence of other characteristics such as community mobility may be diminished in the presence of high ASCVD risk. Indeed, the high-risk ASCVD group averaged approximately 10 points lower on the DSST than the low-risk group. Further research is needed on additional factors that might influence the life-space-cognition relationship among those at risk of ASCVD, how the relationship evolves over time, and how to best incorporate these important measures of cognition and community mobility into clinical practice. Given the complex relationship between mobility, cognition, and ASCVD risk, interventions will likely need to be holistic, incorporating both lifestyle and physiological factors to improve overall health and function among older adults. Study concept and design: All authors. Data collection: Virginia J. Howard. Acquisition of funding: Virginia J. Howard, Emily B. Levitan. Statistical analysis: Emiri Matsuda, Emily B. Levitan. Clinical interpretation and expertise: Michael Crowe, Cynthia J. Brown, MD, Madeline R. Sterling. Drafting of the manuscript: Emiri Matsuda, Emily B. Levitan. Critical revisions of the manuscript for important intellectual content: All authors. The authors thank the other investigators, the staff, and the participants of the REGARDS study for their valuable contributions. A full list of participating REGARDS investigators and institutions can be found at: https://www.uab.edu/soph/regardsstudy/. Dr. Levitan reports research funding from Amgen, Inc, unrelated to the current work. The other authors do not have conflicts to report. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NINDS or the NIA. Representatives of the NINDS were involved in the review of the manuscript but were not directly involved in the collection, management, analysis, or interpretation of the data. Representatives from NHLBI did not have any role in the design and conduct of the study, the collection, management, analysis, and interpretation of the data, or the preparation or approval of the manuscript. The REGARDS study is supported by cooperative agreement U01 NS041588 co-funded by the National Institute of Neurological Disorders and Stroke (NINDS) and the National Institute on Aging (NIA), National Institutes of Health, Department of Health and Human Services. Additional funding was provided by R01 HL80477 and R01 HL165452 from the National Heart Lung and Blood Institute (NHLBI).