['Clinical studies suggest that vitamin K2 protects against bone loss and fractures; however, its effect on bone quality has never been investigated. We investigated the effect of vitamin MK-7 on undercarboxylated osteocalcin (ucOC), and bone mass and quality.', 'We conducted a randomised, placebo-controlled, double-blinded clinical trial.', 'We investigated the effect of MK-7 375\u2009µg for 12 months on bone mineral density (BMD) measured by dual X-ray absorptiometry (DXA), bone microarchitecture measured by high-resolution peripheral quantitative computed tomography (HRpQCT) and biochemical bone turnover markers in 148 postmenopausal women with osteopenia. All of them were supplemented with calcium and vitamin D.', 'ucOC decreased in the MK-7 group (-65.6 (59.1; 71.0) %) (median (CI)) compared with the placebo group (-6.4 (-13.5; 1.2) %) after 3 months (P\u2009<\u20090.01). HRpQCT after 12 months demonstrated that trabecular number in tibia was unchanged in the MK-7-group (-0.1\u2009±\u20091.9%) (mean\u2009±\u2009s.d.) and decreased in the placebo group (-3.5\u2009±\u20092.2%), trabecular spacing was unchanged in the MK-7 group (+1.2\u2009±\u20098.0%) and increased in the placebo group (+4.5\u2009±\u20099.7%), and trabecular thickness was unchanged in the MK-7 group (+0.2\u2009±\u20091.7%) and increased in the placebo group (+4.0\u2009±\u20092.2%) (between-group changes for all: P\u2009<\u20090.05). There were no significant differences between the groups in HRpQCT-derived parameters at the radius or in BMD at any site.'] Does vitamin K2 ( menaquinone-7 ) prevent age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women?