The Relationship of Early Adiposity Rebound With Accelerated Bone Age and Breast Development in Girls: A Prospective Cohort Study
Authors: Jung Hae Woon , Lee Yun Jeong , Lim Youn-Hee , Kim Johanna Inhyang , Kim Bung-Nyun , Hong Yun-Chul , Shin Choong Ho , Lee Young Ah 
Published: May 2021

Abstract
Introduction: Adiposity rebound (AR) refers to the increase in body mass index (BMI) that follows the BMI nadir in childhood. Earlier AR increases the likelihood of being overweight/obese and may lead to early pubertal advancement, especially in girls. We aimed to evaluate the longitudinal changes in anthropometrics, bone age (BA), and breast development in relation to AR timing in girls. Methods: This study included girls (n = 349) of the Environment and Development of Children (EDC) cohort, a prospective cohort of healthy children started in 2012 with biennial visits to study the effects of environmental exposures on physical and neurobehavioral development. The BMI trajectories of girls with 3 or more measurements between 2 and 8 years of age (n = 242) were visually inspected to determine AR timing. After excluding preterm and multiple births, 204 girls were included and categorized according to the age at AR: group 1 (&lt;3.9 years; n = 34, 17%), group 2 (3.9-5.9 years; n = 55, 27%) and group 3 (≥6 years; n = 115, 56%). AR groups were compared for differences in anthropometric measures, BA progression, and breast development. The relationships between AR and outcomes were analyzed with adjustment for age, gestational age, birthweight, physical activity and diet. Results: At age 2, there were no differences in anthropometric measures. By age 4, group 1 showed higher mean BMI z-scores (0.87) than groups 2 (-0.19) and 3 (-0.45) (P &lt;0.001). The differences in BMI z-scores were significant between all 3 groups at 6 and 8-years (P &lt;0.001, for all). Height differences became significant at 8-years (P = 0.010), with greater mean height z-score in group 1 (0.80) compared to group 3 (0.30). BA progression differed significantly between groups 1, 2 and 3 at 6-years (BA 6.87 vs. 6.44 vs. 6.36 years respectively; P &lt; 0.001) and at 8-years (BA 9.65 vs. 8.82 vs. 8.60 respectively; P &lt; 0.001). The inverse relationship between AR timing and BA remained significant after adjusting for covariates at 6 years (B = -0.222, P = 0.040) and 8 years (B = -0.468, P &lt;0.001). Breast development occurred in 49 girls (24%) by age 8 with increased occurrence in the earlier AR groups: group 1 (n = 16, 47%), group 2 (n = 17, 31%), and group 3 (n = 16, 14%) (P for trend &lt;0.001). When compared to group 3, the earlier AR groups had significantly increased risk of breast development at age 8 (OR 5.1, 95%CI 2.1-12.4 for group 1 and OR 2.4, 95%CI 1.1-5.4 for group 2, P &lt;0.001 for both), after adjusting for covariates (P &lt;0.05, for both). Conclusions: Girls who had earlier AR showed greater BA progression starting at 6 years and continuing at 8 years along with greater height at 8 years. These girls are at risk for early breast development after adjustment for covariates. AR timing may be a predictor for BA progression and onset of breast development in girls.