The objective of the present review of the literature was to evaluate the effect of vitamin K supplementation on the skeleton of postmenopausal women. PubMed was used to search the reliable literature for randomized controlled trials (RCTs) by using the inclusion criteria: >or= approximately 50 subjects per group and study period of >or= 2 years. The results of 7 RCTs that met the inclusion criteria showed that vitamin K (K(1) and K(2)) supplementation reduced serum undercarboxylated osteocalcin levels regardless of dose, but that it had inconsistent effects on serum total osteocalcin levels and no effect on bone resorption. Despite the lack of a significant change or the occurrence of only a modest increase in bone mineral density, high-dose vitamin K supplementation improved indices of bone strength in the femoral neck and reduced the incidence of clinical fractures. Furthermore, a post hoc analysis in a large RCT in Japan showed that high-dose vitamin K(2) supplementation decreased the subsequent incidence of vertebral fractures in osteoporotic postmenopausal women with a history of at least 5 vertebral fractures. The review of the reliable literature showed the effect of high-dose vitamin K supplementation on the skeleton of postmenopausal women mediated by mechanisms other than bone mineral density and bone turnover.