Vitamin K2 – The Essential Bone Ingredient
Fragility fractures are an important source of morbidity, mortality, and cost to society. Osteoporosis (Low mineral bone mass density) ultimately leading to fracture is a major health concern in modern societies.Sub-optimal vitamin K status is associated with increased risk of fracture. Low vitamin K consumption or impaired vitamin K status is associated with a higher risk of hip fracture among older women and men, lower bone mass in older women and men, and increased bone turnover. The relationship between dietary vitamin K intake and bone status has been investigated in several epidemiological studies.
Mechanism of Action:
Vitamin K is a co-factor in a number of biochemical pathways. The most common of these reactions is the vitamin K dependent carboxylation reaction. Osteocalcin is a bone protein synthesized mainly by osteoblasts; when carboxylated, osteocalcin has the ability to bind calcium to bone thereby promoting mineralization. Gamma- carboxylation of the glutamic acid in Osteocalcin is vitamin K dependent and involves the conversion of glutamic acid residues (Glu) to gamma carboxy glutamic acid residues (Gla). Osteocalcin, when under carboxylated, cannot bind to hydroxyapitate in bone and is thus inactive. Serum levels of osteocalcin are a good biochemical marker of the metabolic turnover of bone; a number of clinical studies have been conducted to investigate the effect of vitamin K administration on the carboxylation of osteocalcin, BMD, and thus fracture rates. Various dosages of both phylloquinone (K1) and menaquinone (K2) used in these clinical trials showed that under carboxylated osteocalcin levels declined significantly with Vitamin K supplementation.
The Japanese natto (soy) fermented food contains approximately 998 μg of vitamin K2-7 per 100 gms . Typical intake of fermented natto in Japan is approximately 80 gms per day. Kaneki et al  report that serum MK-7 concentrations were 5.26 ±6.13 ng/mL (mean ± SD) in the Japanese women in Tokyo, 1.22 ± 1.85 ng/mL in the Japanese women in Hiroshima and 0.37 ± 0.20 ng/mL in the British women. Natto is eaten more frequently in Eastern Japan, Tokyo, but less frequently in Hiroshima and is not at all a food item in Britain. Kaneki et al  discovered a statistically significant inverse correlation between incidence of hip fracture, natto consumption and serum MK-7 levels between the three groups.
In a study of 72,327 women, vitamin K intake was inversely related to the risk of hip fractures .
Undercarboxylated Osteocalcin(ucOC) vs Carboxylated Osteocalcin(cOC) vs Fracture Rate:
As mentioned above, epidemiologically, MK-7 concentrations in the serum correlate inversely to the incidence of hip fracture. Tskamoto et al , in a prospective study, administered 50 gms of natto per day to three groups. The concentration of MK-7 was either 865, 1295 or 1730 μg of MK-7 per 100 g. General population in Eastern Japan has 100 gms of natto for breakfast at a time. Tsakamoto  found that the serum MK-7 concentration and γ-carboxylated osteocalcin concentration were both elevated parallel to the administered level of MK-7. This now with the above epidemiological finding relates MK-7 administered level to hip fracture.
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  sites 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 postmenopause 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.