Australian scientists in a breakthrough study have found that the brain controls the formation of bone.
The new findings have revealed that bone formation is delicately orchestrated by the brain, which sends and receives signals through the body's neural and hormone systems.
The neural network which controls appetite and energy also alters bone density.
The researchers say that when we are starving, our brains don't allow us to waste energy by reproducing, making fat or creating new bone.
When we are eating too much, on the other hand, our brains make it easier to reproduce, store fat and create bone.
The study led by Dr Paul Baldock, from Sydney's Garvan Institute of Medical Research using mouse model shows that the neurotransmitter Neuropeptide Y (NPY) directly controls osteoblasts, the cells that make bone.
"It has always been thought that changes in bone mass are purely mechanical - you get heavier and your bones get denser to support the increased load," said Baldock.
"While that's true to some extent, our findings show a sophisticated central surveillance system at work. It's as if the brain, as boss, sends out a global memo saying 'make more bone'.
"Bone-making cells at local level appear to have the ability to fine-tune this directive, like office workers saying 'we're not going to waste time putting on bone here when it's needed more over there'."
"So what happens in practice is that places exposed to more load put on more bone, while those exposed to less load put on less bone," he added.
The researchers claim that an intricate central processing takes place in the hypothalamus, a small yet complex region of the brain that links the nervous and hormone systems.
The findings are published in the international online journal Public Library of Science ONE (PLoS ONE).