Hyperinsulinemia and bone mineral density in an elderly population: The Rotterdam Study

We studied the association between insulin and glucose levels and bone mineral density (BMD) in a population based study of 5931 elderly men and women. Serum insulin was measured 2 h after a nonfasting oral glucose load in subjects not using antidiabetes medication. BMD was measured by dual-energy X-ray absorptiometry in the lumbar spine and the proximal femur. In addition, the participants were asked about fractures in the preceding 5 years. Higher bone mass was associated with higher glucose and postload insulin levels at all sites, as well as with increased waist/hip ratio and body mass index. In men, the mean age-adjusted BMD at the lumbar spine (in mg/cm²) increased 4.64 per mmol/L serum glucose (95% CI 1.46-7.82) and 0.35 per mU/L postload insulin (0.17-0.53). In women, these values were 6.88 (4.37-9.39) for glucose and 0.25 (0.11-0.39) for insulin (for all analyses: p < 0.01). The relations were essentially the same with BMD measured in the femur, as well as after adjustment for waist/hip ratio. After adjustment for body mass index, the associations were reduced and lost statistical significance in women. After excluding subjects with diabetes mellitus, the results remained the same. Subjects with a history of nonvertebral fractures had a lower BMD and lower postload insulin levels than those without. The difference in insulin levels was statistically significant in men only (12.5 mU/L, p < 0.001). Excluding men with diabetes mellitus or further adjustment for waist/hip ratio, body mass index or BMD did not change this difference. These results suggest that increased insulin levels are associated with an increased BMD and might be related to a lower fracture rate.