However, testing in humans won't end for another three years, and there's no guarantee that the drug will work as well in humans as in rats.

The study is published in the August issue of the journal Arthritis & Rheumatism.

Osteoarthritis affects an estimated 10 percent of Americans, and 80 percent of those over 55; women are especially vulnerable.

Hips and knees can be especially susceptible, said Dr. J.C. Gallagher, director of the Bone Metabolism Unit at Creighton University Medical School in Omaha, Neb. "For many, pain on exercise is the major problem. As a result, they stop exercising, and this leads to an increase in body weight which increases the 'load' on the joints and worsens the arthritis."

There are numerous treatments to relieve osteoarthritis pain but none to stop the wear and tear on the bone, joints and cartilage.

Karsdal said it is important to treat both loss of bone and loss of cartilage, the elastic tissue that helps bones tolerate moving against each other. "When bone turnover increases after menopause, due to lower estrogen production, a secondary effect is seen on cartilage, more cartilage is lost," Karsdal said. "Ideally, all drugs that may be developed for osteoarthritis will be able to affect both bone and cartilage, as both are in disequilibrium in osteoarthritis."

In the new study, researchers removed the ovaries of female rats, turning them into rough equivalents of postmenopausal women -- at least when it comes to their skeletons.

Some of the rats received calcitonin or estrogen, while some got nothing; a separate group of rats had no ovary operation.

The researchers found that calcitonin worked better than estrogen at preventing joint deterioration.

"The suggestion from this work is that estrogen deficiency after menopause is important," said Gallagher, who's familiar with the study findings.

Calcitonin is currently available as a nasal spray and an injection, although those forms haven't been investigated as possible osteoarthritis treatments, Karsdal said. In the United States, doctors can use approved drugs for "off-label" uses that are not recommended.

The oral form, which was tested in the study, is not on the market.

The next step in research is to investigate whether calcitonin could bring the development of osteoarthritis to a halt, Karsdal said. Two ongoing studies in humans should hopefully "provide a novel and effective treatment for osteoarthritis," although they won't be finished for three years, Karsdal said.

More information

Learn more about osteoarthritis from the U.S. National Institutes of Health.