Objective: To determine the associations between body composition at baseline and knee cartilage loss over 2.9 years in older adults.

Methods: A total of 395 randomly selected subjects (mean 62 years, range 51-81, 50% female) were studied at baseline and 2.9 years later. T1-weighted fat-suppressed magnetic resonance imaging of the right knee was performed to determine knee cartilage volume and tibial bone area at baseline and follow-up. Height, weight and radiographic osteoarthritis were measured by standard protocols at baseline. Fat mass and lean mass were measured by dual-energy X-ray absorptiometry at baseline.

Results: Tibial cartilage volume decreased by 2.0–2.7% per annum. In multivariable analysis, annual change in medial cartilage volume was negatively and significantly associated with body mass index (β: −0.14% per kg m⁻², 95% confidence interval (CI): −0.25%, −0.02%), percentage total body fat (β: −0.19% per %, 95% CI: −0.30%, −0.07%) and percentage trunk fat (β: −0.10% per %, 95% CI: −0.19%, −0.02%), and positively associated with percentage lean mass (β: 0.20% per %, 95% CI: 0.08%, 0.32%). Change in lateral tibial cartilage volume was also significantly associated with percentage total body fat (β: −0.11% per %, 95% CI: −0.21%, −0.001%) and total lean mass (β: 0.13% per kg, 95% CI: 0.04%, 0.22%). These were independent of sex and age even though both were also significant predictors.

Conclusions: Body fat adversely affects tibial cartilage loss over time, whereas lean mass is protective. Strategies aimed at reducing body fat but increasing lean mass may reduce knee cartilage loss in older people.