Osteoporosis: On the Cutting Edge of Bone Health
Advances in research are changing the way osteoporosis experts think about this widespread disease.
Understanding Bone Remodeling
Bisphosphonate drugs were originally thought of as osteoporosis treatments
that helped to build bone mass. But it soon became clear that something more
was going on here. Many patients taking bisphosphonates may see only a modest
increase in bone density -- as little as 1% -- and yet they have a much greater
reduction in their risk of fractures, as much as 50%.
"Research has shown that there is no relationship between how much these
drugs build bone mass and the reduction in fracture risk," says Robert Heaney,
M.D., a professor of medicine at the Osteoporosis Research Center at Creighton
University School of Medicine in Omaha, Neb.
Scientists realized that the drugs were also slowing down the rate of bone
remodeling -- the process in which existing areas of bone is pared away,
later to be replaced with new bone. In menopausal women, that rate of bone
remodeling doubles -- and then it triples by a woman's early 60s.
"Imagine if you started remodeling your house: first you put an extension on
one side, but before you finished that, you decided to tear out the garage, and
before finishing that, you decided to put a deck on," says Heaney. "You'd have
a pretty fragile house. That's what's happening with accelerated bone
Now that they understand the importance of bone remodeling, osteoporosis
experts are trying to use that knowledge to help predict osteoporosis risk
factors. They're developing tools known as biomarkers, which are chemical
measures of the rate of bone remodeling that can be found in secretions from
blood or urine. There are already biomarkers for the rate of bone remodeling
that work very well in large population studies, says Heaney, but they do not
yet have markers that work well in the doctor's office, on an individual
patient level. Once more accurate biomarkers are developed, these and advanced
imaging techniques may enormously improve our understanding of who is at
greatest risk from osteoporosis.
"This allows us to focus on where the problem really lies: the excess
remodeling that's making bone fragile," Heaney says.
New Osteoporosis Treatments
A few years ago, Heaney saw an 18-year-old girl who'd been in a serious car
accident. She'd escaped with only a few bruises, and X-rays revealed that she
had unusually high bone density. It turned out that her mother, too, had bone
density well above the average. Heaney and his colleagues at Creighton began
studying the entire family -- over 150 people -- and eventually identified what
they call the "high bone mass gene."
A particular mutation in this gene causes the body to make abnormally high
amounts of a protein called LRP5 (low density lipoprotein receptor-related
protein 5). LRP5 influences how much bone is formed and maintained. "None of
the people with the high bone mass gene had ever broken anything, even if
they'd fallen off the barn roof," says Heaney.