Physiology / Science

Scared right down to your bones

If you’re on social media, you’ve probably heard about this in the last week — at least if you frequent the part of the internet that I do! Someone jokingly tweeted that they’d apparently still be scared even when they’re long skeletonised, since now we know that your skeleton has a key part to play in fear.

The good news is, they’re wrong. A skeleton doesn’t have a functional vascular system, so in fact as soon as your blood is gone, so is the fear response. (Brb, asking my GP for this groundbreaking new treatment… Actually, if they say yes, I won’t be back. /dark humour)

The interesting news is that the old theory about adrenaline and the fear response is wrong, or more accurately, it’s incomplete. We knew that already, really, because animals without adrenal glands and people who can’t produce adrenaline can still muster up a fight-or-flight stress response — but this is another piece of the picture. It turns out that within a few moments of being exposed to a stressor, your system is flooded by a hormone that is ultimately produced in your bones: osteocalcin.

The theory that osteocalcin is linked to the stress response has been tested in mice (red flag! mouse physiology is not always identical with human physiology!) in three ways (which is a good way to produce a robust result:

  • Mice were exposed to stressors and then their blood levels of osteocalcin were tested. The stressed mice had elevated levels of osteocalcin, suggesting it is involved in the stress response.
  • Mice were injected with osteocalcin. This induced a stress response, indicating that the link between the stress response and osteocalcin is causative.
  • Mice who were unable to produce osteocalcin were tested with stressors. They were unable to mount a stress response.

On the human front, you can lower that red flag a little! As far as I know, only the first of these three tests has been done on humans, and the results were similar to the mouse study.

Although some of the news sites are quoting people as saying this revolutionises our understanding of the skeleton, proving it’s not just an inert support structure, as always I would sound a note of caution! A very brief search found a 2011 paper about osteocalcin’s role in metabolism, a 2017 paper about cardiovascular risk factors related to a certain form of osteocalcin, and a March 2019 paper about the role of osteocalcin in brain signalling (the opening of which states “It is now generally accepted that the extra-skeleton functionalities of bone are multifaceted”).

This particular study is interesting and understanding the role of osteocalcin in stress could be very useful — but we already knew the skeleton was more than just a physical support!

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