Lower Body Mass Index at Baseline Is Related to Steeper Cognitive Decline in the Alzheimer’s Disease Neuroimaging Initiative Cohort

OBJECTIVE: Midlife obesity is a risk factor for dementia, whereas obesity in older age may be protective of cognition, a phenomenon known as the “obesity paradox.” The mechanisms underlying this phenomenon and the relationship between body mass index (BMI) and cognitive function over time remain unclear. METHODS: In 1399 adults with and without mild cognitive impairment (median age 73.6 years) from the Alzheimer’s Disease Neuroimaging Initiative, we modeled the effects of baseline BMI on within-person trajectories of cognitive decline using Latent Growth Curve Modeling. We also tested if the effects of BMI on cognitive decline are global or specific to memory, executive function, or language. RESULTS: Higher baseline BMI was associated with better memory (β(BMI) = 0.06, p < .05) and worse executive function (β(BMI) = −0.05, p < .05) and not associated with language. Independent of baseline diagnosis, higher baseline BMI was associated with slower rate of decline in executive function, memory, and language (β(BMI) = 0.13, 0.12, and 0.12, respectively; p < .01). Higher BMI was not associated with the intercept (β(BMI) = 0.04, p = .059) or change (β(BMI) = 0.04, p = .415) in a global cognitive factor. CONCLUSIONS: We found that higher baseline BMI was associated with slower cognitive decline in participants with and without mild cognitive impairment diagnosis. Higher BMI in this context seems to be protective of cognitive function for people at risk for dementia. Our findings also support domain-specific effects of obesity on various cognitive functions rather than a final common pathway.