The Natural Cycle and Recycle of Bone

by Jim Sliney, Jr.

Bones – we think of them like we think of scaffolding and beams – hard permanent things. Unfortunately we also think of bones as something that fail as we get older. That’s not the whole story. There is a natural cycle and recycle of bone.

Let’s take a closer look at bone so we can better understand how they work.


This is “Celia.” Celia is an OSTEOCLAST. Osteoclasts, chew up bone. Let’s not blame Celia for being hungry all the time, that’s just what she does. She travels along the surface of bones, which look like this.


As she does, she eats up old bone. Eating bone!?! Don’t worry, it’s not as bad as it sounds.

In fact,

1) Though Celia chews up our bones, it is by that very process that calcium gets released from the bone into our blood stream where we need it for many vital functions, also,

2) There is another type of cell that goes around fixing what Celia breaks up. That cell is called “Barry”.


This is Barry. Barry is an OSTEOBLAST. Osteoblasts build bone. Barry has a lot of work making new bone and fixing up after Celia, but he’s good at his job.

This dance that Celia and Barry perform all the time (yes, even right now as you are reading this), the chewing away of existing bone and building up of new bone, is called “bone resorption”. Build it up here, break it down there, build it up here, break it down there, always on and on as long as you live.

Getting in trouble:

Things start to go wrong when Celia eats more bone than Barry can build. This creates an imbalance in bone resorption in which

  1. Bones start to thin out (OSTEOPENIA), and if not addressed
  2. They can become more brittle (OSTEOPOROSIS) and then,
  3. Sometimes, they can collapse or break (FRACTURES).

Time also presents a challenge. Generally speaking, bones build from birth until about the age of 30 after which time the metabolic energy that drove the bone growth slows considerably. From that point forward, if extra steps are not taken to keep Celia’s appetite in check and to keep Barry working hard, bones can begin to gradually thin out, become brittle, and so on.

Getting out of trouble:

There are drugs available that can slow Celia’s eating. Drugs like Fosamax, Actonel, Boniva and others in a class called Bisphosphonates which are usually taken as pills or intravenous injection. There are others too, like Prolia, which also slow Celia’s eating. Prolia is given by injection. There are even drugs like Forteo which don’t pay much attention to Celia, rather, they give Barry new energy so he can build faster. Forteo is a daily, at-home injection. Drugs have come a long way towards being able to slow bone loss, stop it, or even cause bone growth.

Staying out of trouble in the first place:

Use your bones! There was recently an article on how bones act in space and it basically said, with nothing to do out in zero gravity, bone-building-Barry goes on vacation and bone mass drops drastically! Sorry Barry, you’re not allowed to go on vacation.

Our bones respond to pressure. To keep Barry from going on vacation you have to pick stuff up. There is a relationship between gravity and our ability to push against it. Here on earth we need to keep pushing against gravity to keep our bones strong. If you were only an inch tall your bones wouldn't be very strong because you wouldn’t have to push against gravity so hard. If you were an elephant, your bones would have to be very strong because you’d have to push much harder against gravity. How do you resist gravity?

  • Lift weights
  • Climb stairs
  • Go walking with a backpack on
  • Be a farmer
  • Get down – get back up again – get down – get back up again (isn’t that a dance?)

When you fight gravity, your bones get the message.

Another way to stay out of trouble is to think about Celia’s needs. She eats bone all the time. Sometimes she eats more because she is told there is not enough calcium in the blood. For the blood, the fastest way to get more calcium is for Celia to eat faster!

That’s right, if you don’t have enough calcium in your blood, it makes Celia even hungrier, which is good on the one hand because she gets us the calcium we need, but bad on the other because over time she can eat up too much. So, one of the best ways to keep Celia from eating too much bone is to make sure there is enough calcium in the blood all the time.

To learn more about bone health, download one of our tip sheets.

Download: Facts About Men & Osteoporosis Download: Facts About Menopause, Bone Health, and Calcium