People who took a popular class of osteoporosis drugs known as bisphosphonates lived an average of five years longer than those who didn’t take them, according to a new study published online in 2011 in the Journal of Clinical Endocrinology & Metabolism.

“It certainly was an unexpected finding,” says study author Jackie Center, PhD, an associate professor at the Garvan Institute of Medical Research in Sydney, Australia. “We spent a year and a half trying to find a way to explain why this might not be a real finding, but there was nothing we could find that would explain it beyond the treatment.”

The Australian researchers analyzed data from 2,000 people in an ongoing osteoporosis study and found 121 women and men who had been taking bisphosphonates like alendronate, or Fosamax, and risedronate, or Actonel, for an average of three years.

Among that group, the death rate among women who were older than 75 when they took bisphosphonates was 69 percent lower than expected.

“We found it really surprising,” Dr. Center says.

Researchers say mortality rates are best determined based on 100 person-years. One death per 100 person years means for every 100 people, there would be one death per year. Using that as a measurement, researchers say women on bisphosphonates had a death rate of 0.76 percent per 100 person-years, which was lower than women taking hormone therapy (1.2 percent), women taking calcium and vitamin D (3.18 percent) and women who weren’t taking anything at all (3.46 percent).

Results were similar in men, but the number of men studied was smaller, so researchers say they can’t be as confident about that finding.

John Eisman, PhD, was another author of the study. He says initially his team thought this reduction in mortality risk could have been due to the fact that people seeking treatment were healthier and taking better care of themselves. “But everything we saw made us think these would be people who would do worse and in fact be more likely to die,” he explains.

“The people in the treatment group were sicker by all the measures we had,” Dr. Center adds. “They had lower bone density, more fractures and weighed less, all of which are associated with an increased mortality.”

Researchers also don’t believe the longer lifespans among those on bisphosphonates can be attributed simply to the fractures prevented, despite the association between fracture and increased risk of death. “There were just not enough of these fractures expected and thus prevented to explain the improvement in survival,” Dr. Eisman explains.

He and his team hypothesize the reduced mortality risk comes from the fact that by preventing bone loss, bisphosphonates are also stopping the release into the blood of heavy metals and potentially other toxic materials stored in the skeleton.

“We know the skeleton is a place where the body stores a lot of things, including heavy metals, we are exposed to throughout our life through gas or eating fish or other things,” Dr. Eisman explains. “With age, as the bone is broken down, these toxic materials are released. If we gave people these bisphosphonates, we have previously shown that it decreased that release.”

Researchers say less than one-third of people with osteoporosis are being effectively treated. If that’s due to concerns that bisphosphonates are connected to unusual fractures of the thighbone or osteonecrosis (bone death) of the jaw, researchers hope this data will lessen those fears by showing a positive side-effect, too.

“We are hoping people may look at this and say, ‘Hang on, these drugs look pretty good and pretty safe.’ This is a good side effect,” Dr. Eisman says.

“It adds to the literature that these medications may have positive effects, and they aren’t all negative effects,” agrees Kathy Weber, MD, a sports medicine physician in the orthopaedics department at Rush University Medical Center in Chicago.

She points out a few study limitations – that there are more females than males, and most are Caucasian. “So you can’t generalize to other ethnic groups and races. It adds to the literature, but the message is, there is still a need for more research and to understand the mechanism that’s adding to the benefit of the mortality reduction.”