Tracking of body mass index from childhood to adolescence: a 6-y follow-upstudy in China

Background: Although extensive descriptive research shows that childhood ob esity predisposes a person to adult obesity, little is understood about the dynamics of weight during childhood and the predictors of weight tracking. Objective: Our objective was to examine tracking patterns of body mass inde x (BMI) as well as their predictors between childhood and adolescence. Design: A cohort of 975 Chinese children aged 6-13 y was followed ed for 6 y (1991-1997). Tracking of BMI was defined as an individual maintaining a c ertain status (overweight or underweight) or relative position (relative BM I quartile) over time. Relative BMI related BMI to age- and sex-specific BM I cutoffs. Results: After 6 y, approximate to 40% of the subjects had maintained their relative positions, but 30% had moved into a lower or higher quartile. The BMIs of thin and fat children were more likely to track: 51% and 46% remai ned in the bottom and upper quartiles, respectively. Nearly one-third of th e underweight children remained underweight in 1997. Overweight children we re 2.8 times as likely as all other children to become overweight adolescen ts: underweight children were 3.6 times as likely to remain underweight as adolescents. Parental obesity and underweight, individuals' initial BMIs. d ietary fat intake, and family income helped predict tracking and changes in BMI. Conclusion: In a society undergoing enormous changes in diet and activity. BMI tracking is still very important between childhood and adolescence in C hina.