Vitamin K is important for skeletal health. Vitamin K is essential for the carboxylation of several Gla proteins in bone which are implicated in bone formation and mineralization. These include osteocalcin (OC) and matrix Gla protein (MGP). Carboxylation of the glutamic acid residues of these proteins optimises their function. Vitamin K occurs as either phylloquinone (vitamin K1) which is the major dietary form or menaquinones (MKs or vitamin K2) which are mainly of bacterial origin. MK4 of the vitamin K2 series has additional, carboxylation-independent, functions including the regulation of osteoblastic specific markers such as alkaline phosphatase (BALP), and osteoprotegerin (OPG) and has inhibitory effects on osteoclast activity. Several observational studies have shown that low vitamin K status is associated with low bone mineral density (BMD) and increased fracture risk, although proof of causality is lacking. The results of several placebo-controlled clinical trials of vitamin K1 and MK4 have been conflicting with some, but not all, showing a positive effect of vitamin K1 on BMD or bone turnover. Positive fracture efficacy has been demonstrated with high-dose MK4, although most trials were on Japanese women. These intervention studies may have been hampered by the study design such as inclusion of vitamin K replete subjects or healthy non-osteoporotic women. The use of vitamin K in the prevention of bone loss and/or fractures in high-risk post-menopausal women with osteoporosis who are vitamin K deplete merits further investigations. The prevalence of low vitamin K stores is high in elderly subjects with osteoporosis. Preliminary data in Japanese women suggest that combined treatment with a bisphosphonate and vitamin K, at least vitamin K2 (MK4), appears to have an additive beneficial effect on BMD and bone resorption. There have been no such studies in a caucasian osteoporotic population. We want to test the hypothesis that treatment with bisphosphonates combined with vitamin K, in vitamin K deplete elderly women with osteoporosis, may offer additional benefit on skeletal metabolism and reduction of fracture risk.

The first part will be a cross-sectional study of post-menopausal women with osteoporosis aged between 60-80 years who are on treatment with bisphosphonate. Their vitamin K status will be determined and those patients who are found to have low vitamin K concentrations defined as \<0.35 ug/ml will be invited to take part in an 18 months prospective randomised placebo controlled trial.

Eligible patients will be randomised to 3 arms (35 patients in each arm). All 3 groups will continue to receive weekly oral bisphosphonate (commonly Alendronate 70 mg weekly) and adjunctive calcium/vitamin D supplements (1.0g of calcium and 800 I.U of cholecalciferol). The control arm (Group A) will receive placebo. Group B will receive 1.0mg daily of vitamin K1 and MK4 placebo. Group C will receive vitamin K2 (MK4) 45 mg daily and vitamin K1 placebo. Patients will be seen at baseline and at 3, 6, 12 and 18 months. Changes in BMD at the lumbar spine, hip, fore-arm at 18 months and the biochemical parameters at each time point will be compared between the groups.