May 31, 2011 -- Older people with type 2 diabetes may have a higher risk for fractures that those without diabetes, even though they tend to have less bone density loss as measured by bone mineral density testing.
This paradox has left many questioning whether bone mineral density testing is of any value in older people with diabetes. Now, a new study, appearing in Wednesday's Journal of the American Medical Association, helps answer this question.
Researchers found that femoral neck bone mineral density (BMD) T scores and World Health Organization Fracture Risk Algorithm (FRAX) scores do predict fracture risk in older patients with diabetes. But doctors must also consider a possible further increase in risk due to diabetes when interpreting these scores.
"We found a clear benefit for testing bone mineral density in older [diabetes patients], but the threshold for concern was lower than for people without diabetes," University of California, San Francisco associate professor of epidemiology and biostatistics Ann V. Schwartz, PhD, tells WebMD.
Diabetes and Fracture Risk
Bone mineral density is most often determined using dual energy X-ray absorptiometry, or DEXA, scanning, which measures the amount of low-energy and high-energy beams that pass through the bone during the X-ray.
A BMD T score measures the density of a patient's bone compared to a normal, healthy 30-year-old. A T score that is within 1 standard deviation of a healthy young adult is considered normal, while a BMD greater than 2.5 standard deviations from normal (-2.5) is the threshold for osteoporosis.
Schwartz and colleagues analyzed data from three prospective observational studies which followed 18,000 older people for an average of around 12 years, including 770 women and close to 1,200 men with type 2 diabetes.
Bone mineral density T scores and FRAX scores were both associated with hip and non-spine fracture risk in the diabetes patients.
"A diabetic patient with a T-score of –2.0 had about the fracture risk as a non-diabetic with a T-score of -2.5," Schwartz says.
The new findings confirm that a diabetes patient with a FRAX score of 3% has a higher fracture risk than a non-diabetes patient with the same score, Schwartz says.
It is not entirely clear why older people with type 2 diabetes have a higher fracture risk than people without diabetes, even though their bones may be denser.
Last fall, the FDA greatly restricted use of Avandia due to reports linking it to heart attacks, but Actos is still widely prescribed.
Both drugs are in a class known as thiazolidinediones (TZDs).
In a review of 10 drug trials published in 2009, researcher Sonal Singh, MD, MPH, and colleagues at Wake Forest University found long-term use of TZDs to be associated with a doubling of fracture risk in women with type 2 diabetes.
"A twofold increase in risk is significant, and older [diabetes patients] should be made aware of this if they are taking Actos," Singh says.
He adds that research is needed to determine if widely prescribed osteoporosis treatments lower fracture risk in older diabetes patients, since these patients tend to have denser bones to begin with.