Type 2 diabetes results in high bone mass in elderly women

In spite of higher bone mass, lower bone turnover, fracture risk is similar to nondiabetic individuals.

Issue: October 2006

Elderly nursing home patients with type 2 diabetes mellitus have higher bone mass and lower bone turnover than those without diabetes, but fracture rates are similar. This is most likely due to a higher rate of falls among those with diabetes.

Harald Dobnig, MD, of the department of internal medicine at the Medical University of Graz in Austria, and colleagues undertook a study of women nursing home patients older than 70 to further examine the bone characteristics and the rates of fracture associated with diabetes in this population. Their results were published in the Journal of Clinical Endocrinology and Metabolism.

Study design

The study included 583 women with type 2 diabetes and 1,081 women without diabetes for a control group. Because traveling to study centers would have been difficult for most participants, researchers had five mobile study teams visit nursing homes with ultrasound devices for bone assessment and with equipment for obtaining high-quality blood specimens. Bone measurements were taken at the calcaneus, the distal one-third of the radius and the proximal phalanx of the third finger on the nondominant side; for the calcaneus, measurements resulted in a stiffness index combining speed of sound and broadband ultrasound attenuation.

Patients in the diabetes group were slightly younger than those in the control group, and fewer patients in the diabetes group had a diagnosis of osteoporosis (P=.07). Researchers followed patients for an average of 24.7 months, and during this period 378 control patients (35%) and 216 diabetes patients (37%) died.

Diabetic patients had higher age-, weight- and mobility score-adjusted calcaneal stiffness (–0.03 for diabetic patients vs. –0.52 for control patients, P<.0001). Speed of sound measurements at the peripheral radius (–0.49 vs. –0.81, P<.005) and phalanx (–0.65 vs. –0.79, P<.05) also showed higher bone mass in diabetic patients. “In a step-wise regression analysis, significant independent determinants of calcaneal stiffness in both patient groups were age, mobility status, osteocalcin levels and quadriceps strength,” the investigators wrote.

Bone turnover

Bone turnover was found to be significantly lower in diabetic patients than in control patients. Regression analysis found that in both patient groups, parathyroid hormone was the most important predictor of osteocalcin levels, followed by HbA1c levels. “Independent of serum PTH, patients with higher HbA1c levels had higher calcaneal bone mass and lower bone turnover markers,” the researchers wrote.

The hazard ratio for hip fracture among diabetic patients was 0.90 vs. control patients (95% CI, 0.70-1.34) after adjustment for age and weight. “Although type 2 diabetes mellitus has significant beneficial effects on bone turnover and bone mass, the fracture risk is equal to nondiabetic patients,” Dobnig told Endocrine Today. “This is likely due to an increase in the risk of falls; these two influences seem to neutralize each other.”

Dobnig noted that PTH appears to play a large role in the mechanisms of lower bone turnover and higher bone mass in diabetic patients. “PTH is down-regulated in long-standing type 2 diabetes,” he said. “For a given serum calcium level, PTH was significantly lower, pointing to a change in the calcium set-point for PTH secretion in diabetics. This, as well as the direct inhibitory effect of glycemia, seem to be the main responsible mechanisms for low bone turnover in this clinical setting.”

Nelson B. Watts, MD, and David A. D’Alessio, MD, of the University of Cincinnati College of Medicine in Ohio, wrote an accompanying editorial on type 2 diabetes and the risk of fracture. With regard to the rates of fracture in spite of increased bone mass and decreased bone turnover, they said that “visual impairment, foot problems, cognitive dysfunction, peripheral neuropathy and hypoglycemia … increase the risk of falling and injury.”

Furthermore, they discussed recent findings indicating that the use of thiazolidinediones in treating diabetes may increase bone loss, especially in diabetic women. “TZDs are a relatively new class of oral agents that have rapidly gained wide usage, with an estimated 20 million prescriptions written in 2004,” they wrote. Because of TZDs’ effects on bone and the increased risk of falls, it seems that fracture risk might actually be increased by type 2 diabetes.

“Patients with type 2 diabetes are certainly not protected from fracture and deserve at least the same screening for osteoporosis that is recommended for nondiabetic [patients],” Watts and D’Alessio wrote. – by Dave Levitan

For more information:

Dobnig H, Piswanger-Solkner JC, Roth M, et al. Type 2 diabetes mellitus in nursing home patients: effects on bone turnover, bone mass, and fracture risk. J Clin Endocrinol Metab. 2006;91:3355-3363.

Watts NB, D’Alessio DA. Type 2 diabetes, thiazolidinediones: bad to the bone? J Clin Endocrinol Metab. 2006;91:3276-3278.