In Diabetics, Good Scores on Bone Tests May Not Rule Out Risk
TUESDAY May 31, 2011 -- Although many older diabetics have good bone density scores, they are as prone to fractures as people with osteoporosis, a new study finds.
For people over 65, doctors usually recommend a bone density test to look for signs of bone loss and osteoporosis, but whether those tests are of use in older people with type 2 diabetes has been a question, according to the researchers.
"People with type 2 diabetes have a strange combination," said the study's lead researcher, Ann V. Schwartz, an associate adjunct professor in the epidemiology and biostatistics department at the University of California, San Francisco. "They have a higher fracture risk and they have a higher bone density."
However, she said, "we found that these tests work to predict fracture," though the interpretation of the results needs to be different.
To assess the value of bone density tests in predicting the risk for fractures among diabetics, the researchers looked at two tests of bone strength: bone mineral density, which produces what's called a T score, and the World Health Organization's fracture risk algorithm, called a FRAX score.
"A T score of minus 2.5 or lower is generally considered osteoporotic and at high risk of fracture," Schwartz said. "But if you have someone with type 2 diabetes who has a T score of minus 2, they have about the same fracture risk as a non-diabetic with a T score of minus 2.5," she said.
Doctors should use bone density to screen older adults with type 2 diabetes, Schwartz said, "but they have to realize that the threshold they use to indicate high risk has to be raised."
The report was published in the June 1 issue of the Journal of the American Medical Association.
For the study, Schwartz's team collected data on 9,449 women and 7,436 men who took part in one of three studies, the Study of Osteoporotic Fractures, the Osteoporotic Fractures in Men Study or the Health, Aging and Body Composition study. All participants were in their 70s when their study began.
During almost 13 years of follow-up, 84 hip fractures and 262 other fractures were recorded among the 770 women with diabetes. Among 1,199 men with diabetes, 32 had hip fractures and 133 had other fractures during about eight years of follow-up, the investigators found.
The researchers noted that, among diabetics, fractures were more likely to occur even when bone density tests indicated that there was only a small risk for fracture.
"For a given T score and age, those adults with DM [diabetes mellitus] had a higher risk of fracture than those without DM, consistent with previous studies," they wrote. "Participants with DM also experienced higher fracture rates at a given FRAX score than participants without DM."
Because of this, according to the researchers, doctors should consider people with type 2 diabetes at risk for fractures even when bone density tests indicate that they don't have osteoporosis and, therefore, have a lower risk for fractures.
In addition, Schwartz said that she would start treating diabetic patients for osteoporosis if they had T scores of minus 2.
She noted that standard treatments for osteoporosis have not been studied in diabetics but that they appear to work. "In general, the treatments seem to be as effective in diabetics as in non-diabetics," she said.
Commenting on the study, Dr. Robert R. Recker, president of the National Osteoporosis Foundation, said that "a lot of people with diabetes will be at risk for fracture, and many of them don't have low bone mass."
But he noted that the reasons that someone with diabetes has a fracture risk may not be the same as for a person without diabetes. "So the same treatments may not be appropriate -- and therein lies the rub," Recker said.
He does, however, recommend calcium and vitamin D.
The real problem, he said, is that little is known about why the risk for fracture is elevated among type 2 diabetics.
"Basically, we don't know anything about it," Recker said. "There may be something going on that interferes with bone cell function -- and it's not outrageous to think that because diabetes interferes with just about all cell function all over the body."
The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more on diabetes.
Posted: May 2011