Body Mass Index and Decline in Cognitive Function in Older Black and White Persons.

Background: While body mass index (BMI) is higher in black compared to white persons, little is known about BMI and change in cognition in cohorts with a large proportion of blacks. We examine relations of BMI with decline in global cognition and five cognitive domains, in older blacks and whites, and determine whether relations differ by race.

Methods: Participants were 2,134 persons without baseline dementia (33% black; 75% women; mean age =77.9 [range 53-100] and education = 14.7 years, Mini-Mental State Examination = 28.0), enrolled in one of two longitudinal, community-based cohort studies of aging (Minority Aging Research Study; Rush Memory and Aging Project). Summary scores of global cognition and five domains were based on 19 neuropsychological tests administered annually. Mixed-effects models, controlling for age, sex, education, and race, were used to examine the relation of baseline BMI to change in cognition.

Results: Baseline BMI = 28.4 units (30.3 in blacks [95% confidence interval (CI): 27.2-27.7]; 27.4 in whites [95% CI: 29.8-30.7]). During a mean annual follow-up of 6 years (SD = 4), lower baseline BMI was related to faster decline in global cognition (p = .002), and semantic memory (p < .001) and episodic memory (p = .004), but not working memory, perceptual speed, or visuospatial ability (all p > .08). The relationship of BMI with change in cognition was not modified by race (all p > .09).

Conclusions: Late-life lower BMI relates to faster rates of decline in cognition, specifically semantic memory and episodic memory, in both blacks and whites. The effect of BMI on cognition appears to be similar in both racial groups.