The importance of vitamin K in the prevention and treatment of osteopenia/osteoporosis has just been discounted in a WebMD review (“Vitamin K: No Help for Bone Density“) of research published Oct. 14, 2008, in PLoS Medicine (Cheung A, et al.) In the study, Canadian researchers, not surprisingly, found that taking 5 mg per day of vitamin K1 does not protect postmenopausal women from age-related declines in bone density.
What is surprising is that the researchers, despite noting that vitamin K is a family of compounds, and that vitamin K2 is the form which is an approved treatment for osteoporosis in Japan, chose to use vitamin K1 in their clinical trial.
It is well known that vitamin K1 (phylloquinone) is involved in blood coagulation. It is also well documented that vitamin K2 (menaquinone) is the essential cofactor for the carboxylation (activation) of the (gamma-carboxyglutamic acid) Gla-containing proteins involved in calcium regulation.
Numerous peer-reviewed studies have shown that vitamin K2 – given either as the synthetic form MK-4 (a short-chain version called menatetrenone) at a dosage of 45 mg/day, or as the natural form, MK-7 (a long-chain menaquinone derived from natto) at a dosage of 45 mcg/day – is a highly effective activator of osteocalcin, the Gla-containing protein integral to calcium deposition in bone. This body of research conclusively demonstrates that vitamin K2 not only lessens fracture incidence and improves bone density but also, via the carboxylation of another Gla protein (matrix Gla protein), inhibits arterial calcification.
Finally, even though they did not use the right form of vitamin K, looking at the research more closely shows that in the treatment group fractures were down – only 9 women getting vitamin K1 vs. 20 getting placebo had fractures (which is why we want higher bone density!). In addition, surrogate markers of bone production were up and the trends were toward higher density at several points during the intervention.
Why Cheung et al. did not use the optimal form of vitamin K remains a mystery, as does the lack of critical analysis and incomplete conclusion provided by the review. Hopefully, the outcome of this misleading publication will not be an increased incidence of osteopenia/osteoporosis in women at risk of these conditions who are dissuaded from supplementing with vitamin K2.
Cheung A, Tile L, Lee Y, et al. Vitamin K Supplementation in Postmenopausal Women with Osteopenia (ECKO Trial): A Randomized Controlled Trial, PLOS Medicine, Oct. 14, 2008; Vol 5: p. e196.
Pizzorno L, Pizzorno J. Vitamin K: Beyond Coagulation to uses in Bone, Vascular, and Anti-Cancer Metabolism. IMCJ, Apr/May 2008, Vol 7:No. 2, p.24-30.