Why the flight-or-fight response is about more than adrenaline.

The next time a tense situation jolts you into fight-or-flight mode, you may want to thank your skeleton for that survival impulse.

Scientists have long pointed to adrenaline as the trigger behind the acute stress response. But recent research at Columbia University suggests that the fight-or-flight mode couldn’t happen without osteocalcin, a bone-derived hormone.

“In bony vertebrates, the acute stress response is not possible without osteocalcin,” says lead study investigator Gérard Karsenty, MD, PhD. “It completely changes how we think about how acute stress responses occur.”

Karsenty and his team tracked osteocalcin spikes in lab mice and human study participants during stressful scenarios and found that the hormone boosted heart rate, body temperature, and blood-glucose levels — all signs of the acute stress response. Mice that were genetically engineered to produce no osteocalcin displayed little or no reaction in the same situations.

This makes sense when you consider the protective qualities of our skeletal system, Karsenty notes. “If you think of bone as something that evolved to protect the organism from danger — even the bones in the ear alert us to approaching danger — the hormonal functions of osteocalcin begin to make sense.”

So what is adrenaline’s role in the acute stress response? Scientists are no longer sure. Further research is needed — and Karsenty says it may reveal other surprising interorgan signals.