A type of drug used to treat weak bones is associated with an increased risk of 'micro–cracks' in bone, according to new research.

The early–stage research, by scientists at Imperial College London, suggests these microcracks may reduce mechanical strength of the bone.

In the study, published in the journal Scientific Reports, researchers studied bone samples from 16 people who had been diagnosed with the weak bone condition osteoporosis.

All of the patients had suffered a broken hip, and half of the patients had been taking a type of commonly–prescribed drug called bisphosphonate.

The team then used X–rays from the Diamond synchrotron to visualize the structure of bone at a high resolution.

They found that the bones of people taking the drugs not only had a larger number of tiny cracks, but also had less mechanical strength.

The team said there is now an urgent need to further investigate these findings – though they stressed that patients should not stop taking the medication if they have been prescribed the drugs by their doctor.

Dr Richard Abel, lead author of the research from the Department of Surgery and Cancer at Imperial, said: "Although this is a very small, early–stage study, the results are quite startling, and justify follow–up studies.

"These microcracks are like the small cracks that emerge when you repeatedly flex a plastic ruler – they gradually weaken the structure and may potentially make it more prone to breaking."

Microscale structure of bone is not visible using standard X–ray equipment in labs or hospitals – which is the conventional way bone thinning is detected. Therefore, the researchers used a particle accelerator – the Diamond Light Source in Oxford – to analyse samples of bone.

They studied eight hip bone samples from patients who had suffered a fracture while taking bisphosphonates, and eight samples from patients who had suffered a fracture but had not been taking the medication.

These samples had been collected from patients during hip replacement procedures. The patients were between 60–90 years old.

The team also studied hip bone samples from patients who did not have osteoporosis and had not experienced a hip fracture.

They also tested the mechanical strength of the bone samples.

The results revealed that the bones of people who had been taking bisphosphonates had 24 per cent more microcracks than the bones of people who had not been taking the drugs, and 54 per cent more than healthy ageing bone.

However, as expected, the bones of people who were taking bisphosphonates were also found to have fewer holes.

But despite this, the bones from patients treated with bisphosphonates were also found to be 33 per cent weaker than people who had suffered fractures but were not taking bisphosphonates.

The researchers used various mathematical models to confirm the differences were statistically significant.

Dr Abel explained: "This research suggests that, in a small number of patients, rather than protecting against fractures bisphosphonates may actually may make bones more fragile. We now urgently need larger studies to confirm this finding."

He added that further studies would also provide insight into whether there is an ideal length of time to prescribe the drugs.