TThe "adrenaline rush" in the face of danger is only a medical myth, according to new research.

A series of studies have found that increased heart rate, accelerated breathing, and the temporary increase in physical strength involved in the "fight or flight" reaction are actually triggered by a little-known hormone produced by the bones.

Tests in humans and in animals have shown that osteocalcin was responsible for the acute stress response that helps us out of danger, rather than adrenaline.

Published in the journal Cell Metabolism, the results reverse decades of thinking about the role of adrenaline, produced by the adrenal glands located just above the kidneys.

They also suggest that the skeleton has a much broader evolutionary role to ensure our safety.

Professor Gerard Karsenty of Columbia University said, "The notion that bones modulate the stress response is quite new, as is the notion that the adrenal glands do not mediate the stress response. .

"This confirms the concept that the bone was invented in part as a tool for fighting a serious hazard."

He added: "If you think that the bone has been developed to protect the body from danger – the skull protects the brain from trauma, the skeleton allows vertebrates to escape predators, and even the bones of the ear warn us of the danger – the hormonal functions of osteocalcin begin to make sense. "

A study reviewed by the Columbia team showed that people involved in stressful situations such as public speaking experienced a surge of osteocalcin.

Meanwhile, other research using mice has shown that the peaks of the hormone were accompanied by an increase in heart rate, body temperature, and glucose usually associated with the hormone. ;adrenaline.

Other tests revealed that mice unable to produce adrenaline still exhibited combat or flying characteristics when they were exposed to the smell of fox urine. , signaling a danger.

The studies help explain why young people, whose bones are healthier and more active, have a more acute stress response.

"In bone vertebrates, the response to acute stress is not possible without osteocalcin," added Professor Karsenty.

"It completely changes the way we think about how responses to acute stress occur."

In accordance with previous research on the fight or flight response, the increase in stress-related osteocalcin appears to depend on a region of the brain called the amygdala, also known as the center of fear. of the brain.

However, he did not need the adrenal glands, which the research team described as potentially "indispensable".

They plan to extend their research to primates in order to attempt to map control pathways from brain to bone.