Bone Density and Exercise: What’s the Connection?

PJ Hamel Health Guide
  • If you’re of a certain age—middle age, I like to call it, though who among us will actually live to be 110?—you’ll remember that song that started “Your toe bone connected to your foot bone, your foot bone connected to your ankle bone…” It included a chorus of “Them [actually, “dem”] bones, them bones, them dry bones…”

    Now, probably every bone you’ve ever seen—on the skeleton in the doctor’s office, perhaps something your dog dragged home—looks pretty dry. But that’s because those bones are dead. Living bones are anything but dry and lifeless. On the contrary, they’re changing shape and size all the time. And therein lies our issue with bone density loss.

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    How exactly does bone change? There are two kinds of bone cells whose job it is to “remodel” our bones (i.e., change them in some way). Osteoblasts build new bone. Osteoclasts break down old bone. Thus, old bone is constantly being replaced. That’s the ideal, anyway.

    When we’re young, we have lots of osteoblasts, and they work overtime making bone, while the osteoclasts, fewer in number, are more laid back. As kids and teens, our bones are still growing; so the balance between buildup and breakdown tips in favor of buildup.

    In young middle age, the processes are (or should be) fairly equal. Our bones don’t grow; but neither do they lose density. As we continue to age, however, the osteoclasts gradually take the upper hand, and we lose more bone than we gain. This may also happen as a result of an illness, menopause, or certain drugs.

    So what can we do to slow down or even stop bone density loss? Well, there are drugs; drugs with unpleasant side effects. And hormone therapy, which also comes with negative side effects, like weight gain and an increased risk of breast cancer. And then there’s the cheapest, simplest, least side-effect-laden treatment of all: exercise.

    How does exercise help prevent bone loss? When exercise stresses your bones, they respond by speeding up the “remodeling” process; more osteoblasts are formed, in order to build more bone. It’s just like exercising your muscles; the more you challenge/stress them, the more they grow. On the other hand, the more sedentary you are—the less you “challenge” your bones—the more quickly they lose mass.

    Pretty simple, huh? That’s why weight-bearing exercise is important; it stresses your bones more than non-weight-bearing exercise. Your body steps up the pace of osteoblast production when you lift weights or go for a jog; the osteoclasts gain the upper hand when you sit on the deck (hopefully not with a smoke, because smoking increases your risk for bone loss, too).

    Oh, and one other thing: calcium, which is the major component of bones, isn’t absorbed well unless you exercise enough to create a demand for it. You can actually control, somewhat, how much calcium your bones absorb by how much you exercise.

    Next time, I’ll help you see that exercise isn't necesssarily a dirty word; there can be more to it than a mind-numbing gym workout. In fact, you might even find yourself exercising and enjoying it!

Published On: September 25, 2008