Bone is living tissue: cells constantly dissolve and rebuild it, replacing roughly 10% of the adult skeleton each year.
How it works, step by step
Osteoclasts dissolve small patches of old bone.
Osteoblasts lay down a collagen framework.
Calcium and phosphate crystallize into it, helped by vitamin D and K.
Loading through exercise signals where to build.
Peak bone mass
Most bone mass is built by the late 20s. Weight-bearing exercise, enough calcium, vitamin D and protein help.
Evidence & sources
The adult skeleton is completely replaced roughly every 10 years through remodeling. Evidence: established. Known: Standard bone physiology estimate. Unknown: Rates differ between bone types and with age. Source: US Surgeon General, Bone Health and Osteoporosis: A Report of the Surgeon General (2004).