Objective  To examine body composition in individuals with early AD and without dementia and its relation to cognition and brain volume.

Design  Cross-sectional case-control study.

Participants  Individuals without dementia (Clinical Dementia Rating, 0; n = 70) and with early-stage AD (Clinical Dementia Rating, 0.5 or 1; n = 70) in the Alzheimer and Memory Program at the University of Kansas School of Medicine.

Main Outcome Measures  Participants were evaluated with brain magnetic resonance imaging (MRI), neuropsychological testing, and dual-energy x-ray absorptiometry to determine whole-body fat and lean masses. Body mass index was calculated as weight in kilograms divided by height in meters squared.

Results  Lean mass was reduced in persons with early AD compared with controls without dementia (F = 7.73; P = .006) after controlling for sex. Whole-brain volume (β = .20; P < .001), white matter volume (β = .19; P < .001), and global cognitive performance (β = .12; P = .007) were associated with lean mass (dependent variable) when controlling for age and sex. The total body fat and percentage of body fat values were not different across groups or related to cognition and brain volume.

Conclusion  Loss of lean mass is accelerated in AD and is associated with brain atrophy and cognitive performance, perhaps as a direct or indirect consequence of AD pathophysiology or through shared mechanisms common to both AD and sarcopenia.