Earlier BMI rebound and lower pre-rebound BMI as risk of obesity among Japanese preschool children.

OBJECTIVES: Longitudinal growth data of children were analyzed to clarify the relationship between the timing of body mass index (BMI) rebound and obesity risk in later ages.

SUBJECTS/METHODS: Of 54 558 children born between April 2004 and March 2005 and longitudinally measured in April and October every year in the preschool period, 15 255 children were analyzed wherein no longitudinal measurement is missing after 1 year of age. BMI rebound age was determined as the age with smallest BMI value across longitudinal individual data after 1 year of age. Rebound age was compared between overweight and non-overweight groups. The subjects were divided into groups based on the timing of rebound. The sex- and age-adjusted mean of the BMI, height and weight s.d. scores for age group, along with 6 months weight and height gain, were compared among groups using analysis of covariance.

RESULTS: Among those who were overweight at 66-71 months of age, BMI rebound age obtained at approximately 3 years of age was compared with the non-overweight group, whose BMI rebound age was utmost 66 months or later (P<0.001). The comparison among BMI age group showed that earlier BMI rebound results in larger BMI (P<0.001) and larger weight and height gain after the rebound (P<0.001). Among the group with BMI rebound earlier than 30 months of age, low BMI was observed (P<0.001). Slight elevation of height and weight gain was observed before the BMI rebound among groups with rebound age earlier than 60 months of age (P<0.001).

CONCLUSION: Earlier BMI rebound timing with pre-rebound low BMI leads to greater childhood obesity risk; hence, early detection and prevention is necessary for such cases.