Longitudinal Facial Growth in Extant Humans: Examining the Association of BMI and Sex

OBJECTIVES: Understanding patterns of growth elucidates the mechanism by which adult morphology arises, potentially informing us about the evolutionary history of these traits. We utilize the true longitudinal data from the Iowa Facial Growth Study (IFGS) to examine patterns of facial growth and development in relation to body mass index (BMI) and sex. MATERIALS AND METHODS: Our sample (n = 77; 36 female) includes lateral cephalogram data at ages 4, 6, 8, 10, 12, and 14. Coordinate landmarks capturing facial shape were used to study facial size, facial shape, and facial form across growth. Cervical vertebral maturation was used as a secondary metric for skeletal maturation. We employed traditional and longitudinal statistics, such as mixed effects models, to examine trends in the data by BMI and sex. RESULTS: High BMI children have larger facial centroid sizes at Age 4 and maintain this trend through growth. Interestingly, unlike what is seen in dental development, this advanced skeletal development is not coupled with an apparent acceleration in the rate of skeletal development. We further can detect sex differences in facial size as young as the starting Age 4 timepoint (p = 0.0014). Longitudinal analysis revealed differences in facial form early in ontogeny (Age 4), with all BMI groups nearing convergence at the final timepoint (Age 14). DISCUSSION: Our work demonstrates that variation in facial growth patterns related to BMI and sex is established early and maintained across growth. The growth of the craniofacial skeleton is likely influenced by a complex combination of genetic and environmental factors.