Impaired gamma carboxylation of osteocalcin in elderly women with type II diabetes mellitus: relationship between increase in undercarboxylated osteocalcin levels and low bone mineral density

We conducted a cross-sectional examination of the role of serum vitamin K levels as they relate to bone metabolism in elderly women with type II diabetes mellitus (DM). Eighty-five elderly women with type II DM were enrolled. Three fractions of vitamin K, phylloquinone (PK), menaquinone 4 (menatetrenone; MK 4), and menaquinone 7 (MK 7), along with undercarboxylated osteocalcin (UcOC), intact osteocalcin (IOC), urinary deoxypyridinoline (udpd), urinary type I collagen N-telopeptide (NTx), and intact parathyroid hormone (IPTH) were measured. Bone mineral density was measured in the lumbar spine (LSBMD) by dual-energy X-ray absorptiometry (DXA), and T scores or Z scores were calculated. The patients were divided into two groups by T score, under −2.5 (osteoporotic group) and over −2.5 (non-osteoporotic group). UcOC levels in osteoporotics patients were significantly higher than those in the non-osteoporotic group (3.09 ± 3.94 vs 1.82 ± 1.76 ng/ml, P = 0.02). The correlation between Z score and logarithmic UcOC/IOC levels in type II DM showed a negative trend (P = 0.07) and a significantly and negatively association with logarithmic NTx (r = −0.38; P = 0.001). In osteoporotic DM, the UcOC/IOC ratio was significantly correlated with the Z score (r = −0.61; P ≪ 0.05). Furthermore, logarithmic UcOC/IOC showed a negative correlation with logarithmic MK 7 (r = −0.50; P = 0.001). In conclusion, the reduction in LSBMD in elderly women with type II DM may be associated, in part, with a defect in Γ-glutamylcarboxylation by vitamin K.