Body Mass Index Trajectories in Relation to Change in Lean Mass and Physical Function: The Health, Aging and Body Composition Study

ObjectivesTo examine body mass index (BMI) trajectories with change in lean mass and physical function in old age. DesignProspective cohort study. SettingHealth, Aging and Body Composition Study. ParticipantsBlack and white men (n=482) and women (n=516) aged 73.12.7 and initially free of disability. MeasurementsA group-based trajectory model was used to determine BMI trajectories, the path a person's BMI followed over 9years. Lean mass, gait speed, grip strength, and knee extension strength were assessed at baseline and after 9years, and relative changes were calculated. Multivariable linear regression was used to determine associations between trajectories and relative change in lean mass and physical function. ResultsFour BMI trajectories were identified for men and four for women. Although all demonstrated a decline in BMI, the rate of decline differed according to trajectory for women only. Men in Trajectory 4 (mean BMI at baseline 33.9 +/- 2.3kg/m(2)) declined more than those in Trajectory 1 (mean BMI at baseline 22.9 +/- 1.6kg/m(2)) in gaitspeed (-9.91%, 95% confidence interval (CI)=-15.15% to -4.67%) and leg strength (-8.63%, 95% CI=-15.62% to -1.64%). Women in Trajectory 4 (mean BMI at baseline 34.9 +/- 3.0kg/m(2)) had greater losses than those in Trajectory 1 (mean BMI at baseline 20.5 +/- 1.6kg/m(2)) in lean mass in the arms (-3.19%, 95% CI=-6.16% to -0.23%). No other associations were observed. ConclusionObese men had the highest risk of decline in physical function despite similar weight loss between trajectories, whereas overweight and obese women who lost the most weight had the greatest risk of lean mass loss. The weight at which a person enters old age is informative for predicting loss in lean mass and physical function, illustrating the importance of monitoring weight.