Most people know that adequate calcium intake is essential for healthy bone formation. In 2011, the benefits of calcium were called into question when a research study found that calcium supplementation was linked to a higher risk of heart attacks and strokes.1 This news sent shockwaves through the medical and scientific communities as they searched to make sense of this evidence. What was overlooked in that study is that even though calcium is essential for building bone, it requires other vitamins, minerals and co-factors to be properly used.
While the connection between vitamin D and calcium levels for bone health is well known, the relationship between vitamin K and calcium is relatively new. Vitamin K is actually a family of molecules with a number of unique forms. Vitamin K1 (phylloquinone) is found in plants; vitamin K2 (menaquinone) is formed by bacteria after fermentation. Vitamin K2 is further divided into MK-4 and MK-7 forms.2,3 In relation to bone health, vitamin K regulates osteocalcin, a protein important for bone mineralization.4,5 A simple way of looking at osteocalcin is that it almost acts as a sticky glue for calcium to become attached to the new bone. Studies have also shown that vitamin K supplementation can also improve osteoporosis and reduce fracture rates.10
The other essential role of vitamin K in relation to calcium balance is that it can prevent soft tissue calcification. Vitamin K controls a protein that is responsible for protecting soft tissues like blood vessel walls and prevents excess calcium from being deposited. It acts as a calcium mop in areas of the body that should not be hardened or calcified. The ability of vitamin K to not only increase calcium usage in bone formation but also prevent the calcification of arteries clearly highlights its importance in both bone and cardiovascular health. In light of the study mentioned at the beginning of this article linking calcium usage to cardiovascular health, vitamin K seems to be the neglected factor in preventing a hardening of arteries which can lead to an increased risk of heart attacks and strokes.
A note about forms and dosage of vitamin K
Recently there has been some confusion about whether the MK-4 or MK-7 forms of vitamin K2 are most effective at lower doses. MK-4 is considered the “active” form of vitamin K2 and is slowly converted from MK-7. The vast majority of the studies showing vitamin K2 reducing fracture risk have only used the MK-4 form at 25-90mg daily.6 The advantage of MK-7 is that it may be more bioavailable at lower doses found in Canadian vitamin K supplements (100mcg is the high level allowed by Health Canada) since it lasts longer in the bloodstream. In light of this most recent research and the balance of the existing evidence, a combination of both MK-4 and MK-7 may be the most effective approach in order to harness the benefits of both forms at low doses.7
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1) Bolland et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010 Jul 29;341:c3691
2) Kidd PM. Vitamins D and K as pleiotropic nutrients: clinical importance to the skeletal and cardiovascular systems and preliminary evidence for synergy. Altern Med Rev. 2010 Sep;15(3):199-222.
3) Booth SL Roles for vitamin K beyond coagulation. Annu Rev Nutr. 2009;29:89-110.
4) Oldenburg et al. The vitamin K cycle. Vitam Horm. 2008;78:35-62.
5) Berkner KL. Vitamin K-dependent carboxylation. Vitam Horm. 2008;78:131-56.
6) Shiraki M, Shiraki Y, Aoki C, Miura M. Vitamin K2 (menatetrenone) effectively prevents fractures and sustains lumbar bone mineral density in osteoporosis. J Bone Miner Res. 2000 Mar;15(3):515-21
7) Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. 2012 Nov 12;11:93.