There is an increasing amount of talk these days about the importance of vitamin K2, a nutrient that was previously overlooked or "forgotten" in the context of health. Although many people are familiar with K1 for use in the regulation of normal blood clotting, K2 actually has a very distinct role and is therefore best treated as a separate vitamin altogether. K2 plays a major role in the health of the heart, blood, bones, skin, and immune system and even fights cancer. It is also extremely important in the effective use of both calcium and vitamin D.
There are actually three types of Vitamin K, which is a fat-soluble vitamin. The first and most well known variety is K1, which is not only important for healthy blood coagulation, but also necessary for preventing calcification in the blood vessels as well as insure proper calcium retention in the bones. K1 is found in green leafy vegetables such as collard greens, kale, spinach, etc. However, the body only absorbs about 5-10% of K1 from vegetable sources, 10-15% if consumed with a fat. Unfortunately, this isn't enough K1 to adequately convert into K2, the type of Vitamin K that many of us are deficient in. Therefore, it's imperative that we find specific food sources of K2 or a good quality supplement. The third type, K3, is a synthetic form and is not effective or recommended as a supplement.
What people don't realize about K2 is that it's extremely important for the proper absorption of calcium. Not only does K2 facilitate transporting calcium directly to the bones and bone marrow, it also prevents calcium build-up in the bloodstream where it can cause heart disease and degenerative diseases. K2's role also inhibits the development of osteoporosis, which occurs due to a lack of calcium in the bone tissue. K2 is also important for preventing arterial calcification, cardiovascular disease, tooth decay, infectious disease and even several types of cancer including lung, liver, leukemia and prostate cancer. In fact a recent study conducted on 11,000 men found that vitamin K2 decreased prostate cancer risk by 35%.
Another key role that K2 plays is that it activates a protein called osteocalcin, which is signaled for production by Vitamin D, a key player in calcium absorption. In fact, without adequate K2, Vitamin D loses its effectiveness impacting over 3,000 genes and 36 organ tissues in the body. Vitamin D is extremely important for quite a few health conditions including cancer, diabetes, mental health, digestive disorders, aging, cardiovascular disease, autoimmune disorders, obesity and more. However, without K2 to direct calcium to the appropriate locations in the body and ensure that these proteins can bind calcium properly, vitamin D's abilities only go so far. Without the combination of both vitamins D3 and K2, the expression of matrix Gla protein (MGP) also won't be activated. This protein is essential for proper bone mineralization and the prevention of calcification in the arteries.
To obtain Vitamin K2, there are various sources, Mk4, and Mk7 being the most common forms. Mk4 can be obtained from animal foods such as eggs, meat and dairy. However, many experts agree that the best source is Mk7, which is a long chain form that stays in the body up to a day. Mk7 can be found in fermented foods such as sauerkraut, cheeses (such as gouda and brie), yogurt, and natto, a fermented soybean commonly found in Japan. To give you an idea of how powerful natto is, it contains 27x more k2 than curd cheese which is already a rich source in itself. Even so, most people can't stomach the smell and texture of natto, making it difficult to rely on as a primary source. However, there are supplements on the market for K2 (many of which are extracted from natto) that are just as effective. And, the good news is that there aren't any known toxicity risks with taking K2. A general recommendation is to take 150 mcg per day.
 Masterjohn, C. (2008, February 14). On the trail of the elusive x-factor: a sixty-two-year-old mystery finally solved. Retrieved from http://www.westonaprice.org/fat-soluble-activators/x-factor-is-vitamin-k2#synergy
 Fassa, P. (2009, December 30). Vitamin k2 helps prevent heart disease and osteoporosis. Retrieved from http://www.naturalnews.com/027832_vitamin_K_osteoporosis.html Pubmed.gov. "Dietary intake of vitamin K and risk of prostate cancer in the Heidelberg cohort of the european prospective investigation into cancer and nutrition (EPIC-Heidelberg)," K. Nimptsch, et. al. The American Journal of Clinical Nutrition, April 2008: 87(4):985-92. http://www.ncbi.nlm.nih.gov/pubmed/18400723
 Mercola, J. (2011, March 26). The missing nutrient to blame for heart attacks and osteoporosis. Retrieved from http://articles.mercola.com/sites/articles/archive/2011/03/26/the-delicate-dance-between-vitamins-d-and-k.aspx
 (n.d.) Retrieved from http://products.mercola.com/vitamin-k/