Bone Growth Regulation: Hormones, Nutrition, Mechanical Loading, and Genetics

Longitudinal bone growth occurs at the epiphyseal (growth) plates via endochondral ossification.

Key Regulators

• Growth Hormone (GH) / IGF-1: Stimulates chondrocyte proliferation, hypertrophy, matrix synthesis. Liver + local production.
• Sex steroids: Estrogen (both sexes) → growth plate fusion (epiphyseal closure). Testosterone → periosteal apposition (bone width). Puberty timing critical.
• Thyroid hormone (T3/T4): Permissive for GH action; deficiency → growth failure.
• Nutrition: Calcium, phosphate, vitamin D (mineralization); protein (matrix); overall calories.
• Mechanical loading: Weight-bearing exercise → Wnt/β-catenin signaling → osteoblast activity. Disuse → bone loss.
• Genetics: Height polygenic (hundreds of loci); mutations cause skeletal dysplasias (e.g., FGFR3 → achondroplasia).

Growth plates fuse irreversibly (females ~14–16, males ~16–18). No growth after fusion.