06.18.2013

SAN FRANCISCO — Insulin resistance — even if it hasn’t yet developed into overt diabetes — may cause bones to weaken, a cross-sectional study suggested.

Among nondiabetic middle-age individuals, each doubling of the Homeostasis Model of Assessment-Insulin Resistance (HOMA-IR) was associated with a 9% to 14% decrease in three markers of bone strength (P≤0.004 for all), according to Preethi Srikanthan, MD, of the University of California Los Angeles.

Increased levels of fasting insulin — but not fasting glucose — were associated with weaker bones, she reported at the Endocrine Society meeting here.

The findings might explain some of the increased fracture risk that is well known in patients with type 2 diabetes, who actually have higher bone mineral density compared with nondiabetics, Srikanthan said in an interview.

“I think it’s concerning because there’s a growing number of people with obesity — and therefore with insulin resistance — and this indicates that in addition to all the other metabolic abnormalities that we worry about in this group of patients we now have to add to that, perhaps, abnormalities in bone strength,” she said.

The study also suggests that measures of bone mineral density might not be sufficient to assess bone quality, she said.

“This suggests that perhaps we should be looking at more the quality and strength of bone with something like a bone strength marker rather than just bone mineral density,” she said.

Srikanthan and her colleagues examined data from 634 men and women ages 40 to 65 (mean age 56.8) who participated in the Midlife in the United States Study (MIDUS) and who did not have diabetes. The participants underwent dual-energy x-ray absorptiometry, which was used to calculate bone mineral density in the lumbar spine and left hip and femoral neck axis length and width.

The median HOMA-IR was 2.47 and the median glycated hemoglobin (HbA1c) was 5.86%.

The researchers examined the relationship between insulin resistance and three composite indices of femoral neck strength relative to load — compression strength index, bending strength index, and impact strength index. All take into account the physical dimensions of the femoral neck, bone mineral density, and load on the bone.

The association observed between a doubling of HOMA-IR and reductions in all three measures of bone strength remained statistically significant after adjustment for age, sex, race/ethnicity, menopause transition stage in women, study site, and body mass index.

In contrast, a doubling of HOMA-IR was associated with an 11% increase in bone mineral density in the femoral neck (P=0.001).

“Looking at these markers in a prospective fashion would be the next step,” she said.

• Reviewed by F. Perry Wilson, MD, MSCE Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner