Bone is primarily a structural and mineral-regulating organ, not an endocrine organ that signals to distant tissues.

Bone was never simply dead scaffolding. Long before the endocrine idea emerged, researchers knew that bone is constantly broken down and rebuilt, stores calcium and phosphate, contains marrow, and repairs itself after fractures.

The narrower old assumption was that the skeleton’s main jobs were structural, mineral, and blood-cell related. It was not generally treated as an organ that also sends hormone-like signals to distant parts of the body.

That changed as researchers identified molecules made by bone cells that circulate through the blood. FGF23 is one of the clearest examples. Bone cells release it, and it acts mainly on the kidneys to help control phosphate levels and vitamin-D metabolism.

Research on another bone-derived molecule, osteocalcin, suggested wider effects on metabolism and other organs, especially in animal studies. Some of those proposed effects remain less certain in humans.

So the change was not from “dead bone” to “living bone.” Bone was already known to be living and dynamic. The newer idea is that the skeleton also participates in endocrine signaling.