Body mass index trajectories from ages 1 to 20: Results from two nationally representative canadian longitudinal cohorts.

Objective: In this study, unique body mass index (BMI) trajectories from ages 1 to 20 years were identified; each trajectory according to socio demographic and family characteristics was described.

Methods: Participants came from two national population surveys (n = 7,253; n = 901) and were aged 1-6 years at baseline. Children were surveyed biennially over eight waves up to 14-20 years of age. BMI trajectories by sex and survey cohort were identified by group-based trajectory modeling. After crossvalidating trajectories between survey cohorts, the characteristics of trajectory membership were assessed by multinomial regression.

Results: Four BMI trajectories were found: low, decreasing, medium, and high. The decreasing trajectory was characterized by an overweight or obese childhood followed by a normal-weight adolescence. The low, medium, and high trajectories were characterized by growth curves culminating, by age 20, to BMI 22.6, 29.3, and 34.9 kg/m(2) , respectively, for males and 20.6, 24.5, and 32.0 kg/m(2) , respectively, for females. Factors associated with the high trajectory included ethnicity and paternal education (female only), large for gestational age, rural area residence, and maternal smoking.

Conclusions: The identification and validation of four major trajectories reflect the heterogeneity in patterns of BMI development from 1 to 20 years.