Digit symbol substitution test and future clinical and subclinical disorders of cognition, mobility and mood in older adults

© The Author 2016. Published by Oxford University Press on behalf of the British Geriatrics Society. All rights reserved. Objective: to examine whether psychomotor speed predicts individual and combined disorders in cognition, mobility and mood and if white matter hyperintensities explain these associations.Design and setting: longitudinal; Cardiovascular Health Study.Subjects: 5,888 participants (57.6% women, 15.7% black, 75.1 (5.5), mean years (SD)).Methods: psychomotor speed (Digit Symbol Substitution Test (DSST)) and small vessel disease (white matter hyperintensities (WMH)) were measured in 1992-94. Global cognition (Modified Mini-Mental State (3MS) examination), mobility (gait speed (GS)) and mood (Center for Epidemiologic Studies Depression (CES-D) scale) were measured annually over 5 years and classified as clinical, subclinical or no disorders based on established values (3MS: 80 and 85 points; GS: 0.6 and 1.0 m/s; CES-D: 10 and 5 points). Analyses were adjusted for demographics, baseline status, education, diabetes, hypertension, ankle-arm index.Results: among those with no disorder in cognition, mobility and mood (N = 619) in 1992-94, being in the lowest DSST quartile compared to the highest was associated with nearly twice the odds of developing 1+ clinical or subclinical disorders (N = 413) during follow-up. Associations were stronger for incident clinical disorders in cognition (OR: 8.44, p < 0.01) or mobility (OR: 9.09, p < 0.05) than for mood (OR: 1.88, p < 0.10). Results were similar after adjustment for WMH.Conclusions: slower psychomotor speed may serve as a biomarker of risk of clinical disorders of cognition, mobility and mood. While in part attributable to vascular brain disease, other potentially modifiable contributors may be present. Further studying the causes of psychomotor slowing with ageing might provide novel insights into age-related brain disorders.