Osteoporosis drugs can definitely strengthen bones. However, studies and patient reports over the last four years have uncovered a surprising danger: In some cases, these drugs seem to be breaking bones instead of protecting them.

Now a new study from Sweden has helped put that risk of drug-induced breaks into perspective. The study concluded that the drugs, such as Fosamax, Boniva, Actonel, Atelvia and Reclast, caused one broken femur for every 2,000 people who used them for a year.

In other words, the fractures appear to be so few and far between that the benefit of these drugs outweighs the risk, says Dr. Aurelia Nattiv, director of the UCLA Osteoporosis Center.

“It is encouraging to see this data for patients and physicians,” Nattiv said. “It presents one more piece of evidence from a large number of patients that these are good drugs with rare side effects.”


Osteoporosis is a disease that makes bones weak and brittle with age. About 10 million Americans already have the condition, according to the National Osteoporosis Foundation. Half of all women and a quarter of all men over the age of 50 will suffer an osteoporotic fracture at some point in their lives. Bone breaks from osteoporosis can happen in any bone, but are most commonly seen in the hips, the spine and the wrist.

Just as the skin constantly makes new cells to replace old ones, bones go through constant turnover. The osteoporosis drugs, known as bisphosphonates, work by slowing down the cells that break down old bone tissue to make way for new bone. This tips the balance toward denser, stronger bones.

And yet, as the drugs are incorporated into bone tissue, they also affect bone structure. It’s not clear how this may lead to the specific type of breaks seen with the drugs, known as atypical subtrochanteric fractures.

The drugs have been on the market for 16 years and have quickly become the “gold standard” of osteoporosis treatment, Nattiv says.


The new study, published this month in the New England Journal of Medicine, included every Swedish woman who was at least 55 years old and had a femur (thighbone) fracture in 2008, according to a national registry of patients. Researchers were able to study the X-rays of the women with possible atypical fractures and identified 59 cases.

Of these 59 women, 46 had taken bisphosphonates — out of a total of 83,311 Swedish women who took the drugs that year. That was a fracture rate of less than 0.1%. The 13 other women with atypical fractures did not take the drugs, along with 1.47 million other Swedish women. That worked out to a fracture rate of less than 0.001%.

Adjusting for patients’ ages, the researchers calculated that taking the drugs increased the risk of an atypical fracture by 47%. That may sound like a lot, but patients taking the drugs should be reassured that very few women ever suffer such a break whether they are taking the drugs or not, says study coauthor Dr. Per Aspenberg of Linkoping University in Sweden.

Aspenberg uses lightning to illustrate the difference between what sounds like a big relative risk and a very small absolute risk. On a sunny day, the risk of being killed by lightning is basically zero. On a rainy day, the risk might be 1,000 times higher, but it’s still very small.


The ability of the drugs to prevent fractures has been proved beyond any doubt. Dr. David Newman, director of clinical research at Mount Sinai Hospital in New York, who writes about evidence-based medicine, recently boiled the numbers down. For every 100 women taking bisphosphonates for three years, he calculates that six avoid a fracture. The protection is best for fractures of the spine (1 in 20 women), but is also significant for hip fractures (1 in 100).

Newman warns that these numbers apply only to patients with established low bone density or a history of fractures. In patients who don’t meet these criteria, the benefit disappears.

“The rare side effects are very real,” he says. (In addition to atypical fractures, bisphosphonate drugs have been linked to osteonecrosis of the jaw, a bone-killing infection triggered by dental work.) Newman is especially concerned that the big marketing campaigns behind these drugs will put them into the hands of people who don’t really need them. Such people, he says, would be taking on the risks without reaping any benefit.

When the first reports of atypical fractures came out, many patients stopped taking their bisphosphonate medications. “We were getting flooded with phone calls after the initial data [were] released,” Nattiv says. The new study helps put the risk in better perspective, she says: “The data bear out the benefits.”


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