Vitamin D has received a lot of interest in the last few years as an essential nutrient to possibly help prevent serious health issues. Not as much thought has been given to its helper Vitamin K, but I think this is going to change. Several of the conditions that are thought to be associated with vitamin D deficiency, such as osteoporosis, cardiovascular disease, and cancer, as also linked with vitamin K deficit.
Like vitamin D, vitamin K is a fat-soluble vitamin that occurs in several forms. The most commonly known form is vitamin K1, which is necessary for proper blood clotting. Vitamin K2 is the form that is gaining interest right now for its importance in bone and heart health. Sources of vitamin K2 are natto (fermented soybeans), tempeh, grass fed butter and beef, eggs, cheese, and possibly sauerkraut and other fermented vegetables. It is also sold as a dietary supplement under the name MK-7, which stands for menaquinone-7 the scientific name for vitamin K2.
Most of what vitamin K does in the body is help different protein handle calcium, but it is through the appropriate use of calcium that vitamin K has so many benefits.
Vitamin K helps certain proteins hold on to calcium. For instance in bone formation, a protein called osteocalcin needs vitamin K to be able to deposit calcium in the bones. This is why the combination of calcium, vitamin D, and vitamin K was superior for helping improve bone density than was calcium and vitamin D alone in a 2012 study.
Some recent studies have linked calcium intake to increased hardening of the arteries. My hypothesis is that if we don’t have adequate vitamin K2, taking calcium may be an issue for heart health. Vitamin K2 is an essential part of a protein in our artery walls that helps prevent calcium from being deposited in the arteries. Indeed, a few studies have demonstrated that higher vitamin K2 intake is associated with lower rates of cardiovascular disease. So I always tell my patients if they take calcium, make sure they also have adequate levels of vitamin D and vitamin K2 to help ensure the calcium is going to the bones where we want it and not to the arteries.
Dr. Laurell Matthews, ND 
Laurel, this was a very valuable article. My doctor recently prescribed Vitamin K , and this just reinforces her recommendation.
Glad to hear it. I think the interest in K2 will keep increasing.