Association of serum undercarboxylated osteocalcin with serum estradiol in pre-, peri- and early post-menopausal women

Objective: We investigated changes in serum concentration of undercarboxylated osteocalcin (ucOC), which is a sensitive marker of vitamin K status, and association of ucOC concentration with estradiol concentration in pre-, peri and early post-menopausal women. Methods: The study population consisted of 193 pre-, peri- and post-menopausal Japanese women aged 39-66 yr. Serum ucOC concentration was measured to assess vitamin K status; serum concentrations of intact osteocalcin (OC) and bone-specific alkaline phosphatase (BAP) were measured as bone formation markers; and urine concentration of N-telopeptide was measured as a bone resorption marker. Serum estradiol and estrone concentrations were measured by a highly sensitive radioimmunoassay. Bone mineral density (BMD) was measured at the lumbar spine. Results: Serum concentration of ucOC in peri-menopausal women was significantly (p=0.0005) higher than that in pre-menopausal women, while serum OC concentration in post-menopausal women for whom 1 yr had passed since menopause was significantly (p=0.6003, p=0.024, respectively) higher than the concentrations in pre-menopausal and perimenopausal women. Serum ucOC concentration showed a significant negative correlation with estradiol concentration (r=-0.372, p < 0.0001) and a significant positive correlation with serum FSH concentration (r=0.324, p < 0.0001). Serum OC concentration was positively correlated with serum FSH concentration (r=0.317, p < 0.001). Conclusions: The results showed that the change in ucOC concentration during the menopausal transition is different from that in OC concentration. In addition, serum ucOC concentration is closely associated not only with FSH concentration but also estradiol concentration.