High-dose vitamin K supplementation reduces fracture incidence in postmenopausal women: a review of the literature

Although systematic review and meta-analysis of randomized controlled trials (RCTs) have concluded that vitamin K is effective in preventing fractures, the effect of vitamin K on the skeleton remains a matter of controversy. 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 RCTs by using the search terms "vitamin K₁ or vitamin K₂," "bone," and "postmenopausal women" and the following inclusion criteria: approximately 50 or more subjects per group and study period of 2 years or longer. Seven RCTs met the inclusion criteria. The results of these RCTs showed that vitamin K₁ and vitamin K₂ 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 K₁ and vitamin K₂ supplementation improved indices of bone strength in the femoral neck and reduced the incidence of clinical fractures. The review of the reliable literature confirmed the effect of vitamin K₁ and vitamin K₂ supplementation on the skeleton of postmenopausal women mediated by mechanisms other than bone mineral density and bone turnover.