Osteocalcin carboxylation is not associated with body weight or percent fat changes during weight loss in post-menopausal women

Osteocalcin (OC) is a vitamin K-dependent bone protein used as a marker of bone formation. Mouse models have demonstrated a role for the uncarboxylated form of OC (ucOC) in energy metabolism, including energy expenditure and adiposity, but human data are equivocal. The purpose of this study was to determine the associations between changes in measures of OC and changes in body weight and percent body fat in obese, but otherwise healthy post-menopausal women undergoing a 20-week weight loss program. All participants received supplemental vitamins K and D and calcium. Body weight and body fat percentage (% BF) were assessed before and after the intervention. Serum OC [(total (tOC), ucOC, percent uncarboxylated (% ucOC)], and procollagen type 1N-terminal propeptide (P1NP; a measure of bone formation) were measured. Women lost an average of 10.9 +/- 3.9 kg and 4 % BF. Serum concentrations of tOC, ucOC, % ucOC, and P1NP did not significantly change over the twenty-week intervention, nor were these measures associated with changes in weight (all p > 0.27) or % BF (all p > 0.54). Our data do not support an association between any serum measure of OC and weight or % BF loss in post-menopausal women supplemented with nutrients implicated in bone health.