SERUM UNDERCARBOXYLATED OSTEOCALCIN CORRELATES WITH HIP BONE-MINERAL DENSITY IN ELDERLY WOMEN

We previously showed that circulating undercarboxylated osteocalcin (u cOC) is elevated in elderly women and is a powerful marker of the subs equent risk of hip fracture in elderly institutionalized women (J Clin Invest 1993; 91:1769). To investigate the relationship between bone m ass and ucOC, we measured bone mineral density (BMD) of the hip with d ual-energy x-ray absorptiometry in 98 elderly institutionalized women, 81.4 +/- 6.0 years old. ucOC was negatively correlated with BMD at al l sites (r = -0.26 to -0.38, p < 0,001 to p < 0.0001), even after excl usion of the effect of age by partial correlation (for the femoral nec k, r = -0.26,p < 0.01) and after controlling for serum parathyroid hor mone. BMD was significantly lower at all sites of measurement in women with elevated ucOC (>1.65 ng/ml, upper limit of the normal range in y oung women) than in those with normal ucOC (for the neck, 0.58 +/- 0.1 3 versus 0.43 +/- 0.13 g/cm(2), p < 0.001). Similar results were obtai ned for ucOC expressed as the fraction of total OC (ucOC %). Multiple regression showed that ucOC has the highest predictive value for BMD w hen including age and body weight in the equation. In summary, our dat a indicate that serum ucOC is an independent determinant of BMD of the hip in elderly women. The mechanism by which serum ucOC is related to bone mass is unclear and should be addressed in further studies. Howe ver, our data suggest that ucOC level may be an interesting marker in the investigation of bone status in the elderly.