There are several studies relating high prevalence of disease and drug specific osteopenia and osteoporosis relating to vitamin K status. Schoon et al , in a 32 patient Crohn's disease study, conclude ucOC inversely associated with bone mineral density.
Tamatani et al  concluded that vitamin K1 and MK-7 were significantly, positively correlated with bone mineral density.
Kanai et al  observed low BMD in women with lower serum vitamin K1 and K2.
Hodges et al  cites that vitamin K2 may be up to 25 times more active than vitamin K1. His study of 29 patients with fracture, 17 controls, concluded that vitamin K1 and K2 were significantly lower in the fracture group than in the control group.
Takahashi et al  carried out a study to determine effect of vitamin K vs. that of vitamin D. They concluded that ucOC decreased significantly in the groups receiving vitamin K (vitamin K only and vitamin K+D); whereas in the vitamin D-only group ucOC did not change significantly. Why bone loss is predisposed in microgravity is unknown but the ucOC lowering in the cosmonauts is controlled by vitamin K supplementation . Females having strenuous life style are prone to hypoestrogenism and amenorrhoea. As a consequence a low peak bone mass and rapid bone loss is often seen in relatively young athletes.
Craciun et al  working with 8 female marathon runners observed in all subjects increased vitamin K was associated with an increased calcium-binding capacity of osteocalcin. In the low-estrogen group vitamin K supplementation induced a 15-20% increase of bone formation markers and a parallel 20- 25% decrease of bone resorption markers. This shift is suggestive for an improved balance between bone formation and resorption.
Sokoll et al  show a significant reduction in ucOC with vitamin K supplementation.
Recent studies (2008) of Tsugawa et al  relate a significantly higher incidence of vertebral fracture of 14.4% in the low vitamin K group to 4.2 % in the high vitamin K group. This study involved a cohort of 379 healthy women aged 30-88 years.
Lucas et al  (2006) conclude that premenopausal women show reduced BMD despite normal estrogen profiles. %ucOC may be a specific bone marker of the early post-menopause in healthy women.
In a randomized, open-label study , 241 osteoporotic women were given either 45 mg/day vitamin K2 or 150 mg elemental calcium (treatment group; n=120) or 150 mg elemental calcium (control group; n=121). After two years, vitamin K2 was shown to maintain lumbar BMD. Patients receiving K2 also experienced significantly lower fracture incidence (10% versus 30%, in the treatment and control groups, respectively.
Marieke et al in their study  'The effect of menaquinone7 (vitamin K2) supplementation on osteocalcin carboxylation in healthy prepubertal children' showed that supplementation with MK-7, one of the vitamin K2 species, during 8 weeks reduces the amount of circulating ucOC and thereby improves vitamin K status in healthy prepubertal children.
Boland et al in a trial , 'Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial', observed that Calcium supplementation in healthy postmenopausal women is associated with upward trends in cardiovascular event rates.
In another study  Ness J compared occurrence of atherosclerotic vascular disease between women with osteoporosis than with no osteoporosis or osteopenia.
L. C. Hofbauer et al  evaluated potential mechanisms of the osteoporosis-arterial calcification syndrome.
Meta-analysis by Bolland et al, [20-21] showed that calcium supplements (with co-administered vitamin D) are associated with an increased risk of cardiovascular events especially myocardial infarction
In essence, vitamin K2 is necessary for the body to direct calcium to the bones, where it's needed, instead of to the arteries, where it can lead to cardiovascular disease.
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21) Bolland MJ et al, Calcium supplements with or without Vitamin D and risk of cardiovascular events: reanalysis of woman's health initiative limited access dataset and meta analysis BMJ 2011:342:d2040
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