 Results from several studies show that vitamin K has an important function in bone metabolism. In a previous cross-sectional study conducted by our department, evidence for a poor vitamin K status of bone during growth in children was found unpublished data, accepted for publication Pediatric Research, october 2006. These findings justify clinical intervention studies in which bone quality is monitored as a function of long-term vitamin K-supplementation. Before a long-term intervention study is undertaken, it is important to determine the effect of vitamin K administration on osteocalcin carboxylation in this specific population. Although the relationship between increased vitamin K intake and osteocalcin carboxylation was already clearly demonstrated in several adult groups e.g. healthy adults, postmenopausal women, this has never been shown in children. 