Even the small increase in bone mass offered by osteoporosis drugs translates to a reduction in fracture risk, new Canadian research says.

“Often we get women who come into the office for follow-up and if the bone density goes up only 1 percent, they are disappointed and say, ‘Well this drug isn’t working for me,’” says study author Dr. Jonathan Adachi. “This study says, in fact, it is working for you.”

Adachi, who is director of the Arthritis Centre at St. Joseph’s Hospital-McMaster University in Hamilton, Ontario, presented his findings Oct. 25 at the American College of Rheumatology’s annual scientific meeting in Orlando, Fla.

Adachi reviewed the progress of more than 2,000 women who received the bone-building drug risedronate (Actonel) and nearly 1,200 who received a placebo. All the women also took 1,000 milligrams of calcium a day and up to 500 International Units of vitamin D if their levels were low. Bone density at the lumbar spine was measured at the start of the study and periodically during the next three years. X-rays of the vertebrae were obtained at the start and annually for three years.

Adachi compared the estimated risk of a new vertebral fracture between patients who had an increase in bone density and those who had a decrease.

“If the women lost bone density, 15 percent of them had a fracture,” he says. “If they gained zero to 5 percent bone density, 9.5 percent of them had a fracture. If they gained more than 5 percent bone density, 10.2 percent fractured.”

“If the bone density goes up 9 percent, it’s not much better than if it goes up 1 percent,” Adachi says. “And that’s the point.”

Osteoporosis is a disease in which bones become fragile and more susceptible to fractures. About 10 million Americans have the disease, which affects four times as many women as men, according to the National Osteoporosis Foundation.

Adachi’s research suggests the bone-building drugs may be affecting the structure of bone through mechanisms other than density, says Dr. Nelson Watts, director of the University of Cincinnati’s Bone Health and Osteoporosis Center. These mechanisms might include the architecture or geometry of the bone, he says, or physical properties besides density.

The Adachi study, Watts adds, builds on prior studies that have found the same reduction in fracture risk with modest increases in bone density.

“It’s important for patients to have reasonable expectations” about the drugs’ effects, Watts says. And doctors should not go strictly by the amount of bone density changes when determining whether the drugs are working for individual women.

In another presentation at the meeting, researchers reported that back pain in women with osteoporosis can be prevented for up to 18 months after the end of treatment with a drug called teriparatide (Forteo). An injectable hormone-based drug, teriparatide is used to treat osteoporosis. In the study, patients taking teriparatide were 61 percent less likely to experience severe back pain, a consequence of osteoporosis.

Another study found health-care providers are underprescribing drugs to decrease the fracture risk in patients on corticosteroid medications such as prednisone, which can induce osteoporosis. Researchers reviewed the pharmacy files of more than 200,000 military veterans, paying particular attention to approximately 16,000 people who had been given oral corticosteroids to treat other conditions, such as asthma.

Only one-third of those patients also got treatment to prevent bone loss. In those who took prednisone for three months or longer during any year of the four-year study, the fracture risk was 30 percent higher than in those who never took prednisone.