Most people have heard it is important to get enough calcium and vitamin D to grow and maintain strong bones that can resist fractures. But few have heard of the bone strengthening effects of vitamin K. There are two main forms of vitamin K. Vitamin K1 is called phyoquinone or phytonadione and is found mainly in green vegetables like spinach, broccoli, lettuce, and kale. Vitamin K2 is made up of menaquinones that can be synthesized in the human gut by micro-organisms. There are several kinds of these menaquinones and small amounts occur in meats and fermented products like cheeses and natto. However, about 90% of the vitamin K in the American diet comes from vegetables. There is also a synthetic form of vitamin K3 but it is not recommended for human consumption.
People who have heard of vitamin K may be familiar with its important role in blood coagulation but few realize it is also necessary for making a protein called osteocalcin. Osteocalcin is a protein needed to bind calcium to the bone matrix. An inadequate intake of vitamin K may reduce this protein to the point where bone mineral density is reduced and bone structure is compromised.A recent meta-analysis examined 7 studies in which elderly subjects were given either 15 (one study) or 45mg of vitamin K2 or a placebo. Remarkably those taking the supplements of vitamin K had reductions in hip fractures of 77% compared to those given a placebo. Fractures of the vertebrae were cut by 60% and all other fractures were reduced by 81%. None of the individual studies reported any serious side effects from the vitamin K supplements although there did appear to be some increase in GI problems. The authors of this study conclude ?From a clinical perspective, the results of this review suggest that patients at risk for fractures should be encouraged to consume a diet rich in vitamin K, which is chiefly obtained from green leafy vegetables and certain vegetable oils.?1By James J. Kenney, PhD, RD, FACN.1. Arch Intern Med 2006;166:1256-61
