A single injection of stem cells may be able to reverse age-related osteoporosis, according to Canadian researchers.

Osteoporosis occurs when the breakdown of old bone is greater than the creation of new bone. It causes bones to become weak and brittle. As many as half of senior women will break a bone due to osteoporosis.

But what if a single injection could cure it?

In a previous study, Professor William Stanford, senior author of the current study, had demonstrated a link between mice that developed age-related osteoporosis and low or defective mesenchymal stem cells (MSCs).

"We reasoned that if defective MSCs are responsible for osteoporosis, transplantation of healthy MSCs should be able to prevent or treat osteoporosis," said Stanford, who is a Senior Scientist at The Ottawa Hospital and Professor at the University of Ottawa.

For the new study, researchers injected osteoporotic mice with MSCs from healthy mice.

Stem cells are "progenitor" cells, capable of dividing and changing into all the different cell types in the body. In addition to having the capacity to become bone cells, MSCs can also be transplanted from one person to another without the need for matching (needed for blood transfusions, for instance) and without being rejected.

Six months after being injected with the stem cells, which was about a quarter of the animals' life span, the osteoporotic bone had astonishingly been replaced with healthy, functional bone.

"We had hoped for a general increase in bone health," said study co-author John E. Davies of the University of Toronto. "But the huge surprise was to find that the exquisite inner 'coral-like' architecture of the bone structure of the injected animals — which is severely compromised in osteoporosis — was restored to normal."

Researchers say that their results indicate that as little as one dose of stem cells might provide lasting relief.

Currently, a trial is taking place in the United States in which elderly patients have been injected with MSCs, and researchers plan to examine their blood samples for biological markers of bone growth and bone reabsorption.

According to the National Osteoporosis Foundation, 54 million Americans aged 50 and older are affected by osteoporosis and low bone mass. Of those, 10.2 million have osteoporosis and another 43.4 million have low bone mass.