Bone Abstracts

Background: Observations in rodents suggest that osteocalcin (OC) participates in glucose metabolism. Data from human studies are inconclusive and it remains unclear whether OC is simply a marker of bone turnover (BTM) or if it also mediates interactions between the skeleton and glucose homeostasis. This study determined the responses of BTMs, including OC, to oral glucose tolerance test (OGTT) in obese and normal-weight subjects.

Materials and methods: Patients with early-onset severe obesity were recruited from Children’s Hospital, University of Helsinki, and controls from civil register. Subjects underwent a standard 2-h OGTT. Glucose, insulin and six BTMs (BALP, P1NP, TRACP, CTX, and total, and carboxylated OC) were determined at baseline and at 30, 60, 90, and 120 min.

Results: Study included 34 sex- and age-matched case-control pairs (mean age 19±2.3 years). Heights were similar but other anthropometrics were greater in the obese subjects; mean BMIs being 40.4 and 21.9 kg/m². HOMA index was 2.7 times greater in the obese and none were diabetic. All BTMs, except BALP, were significantly lower in the obese compared with the controls: the differences at baseline were 43, 16, 37, 29, and 27% for P1NP, TRACP, CTX, total OC and carboxylated OC (P<0.05 for all). All BTMs decreased during OGTT. When adjusted for baseline values, the OGTT-responses in total and carboxylated OC (measured as AUC) were different between the two groups (P=0.031 and P=0.043 respectively) and the decrease during OGTT was less pronounced in the obese subjects. Responses in other BTMs were similar between the groups (P>0.05).

Conclusions: Bone turnover is substantially lower in obese subjects compared with controls. Total and carboxylated OC showed less pronounced decrease during OGTT in obese subjects compared with controls, while other BTMs responded similarly in the two groups. This supports a role for OC in glucose homeostasis.