Kresser: K2

[A] study recently published by the European Prospective Investigation into Cancer and Nutrition (EPIC) has revealed that increased intake of vitamin K2 may reduce the risk of prostate cancer by 35 percent. The authors point out that the benefits of K2 were most pronounced for advanced prostate cancer, and, importantly, that vitamin K1 did not offer any prostate benefits.

The findings were based on data from more than 11,000 men taking part in the EPIC Heidelberg cohort. It adds to a small but fast-growing body of science supporting the potential health benefits of vitamin K2 for bone, cardiovascular, skin, brain, and now prostate health.
[A] popular misconception is that vitamins K1 and K2 are simply different forms of the same vitamin – with the same physiological functions.
[Vitamin K'2s role includes] protecting us from heart disease, ensuring healthy skin, forming strong bones, promoting brain function, supporting growth and development and helping to prevent cancer – to name a few. In fact, vitamin K2 has so many functions not associated with vitamin K1 that many researchers insist that K1 and K2 are best seen as two different vitamins entirely.
[Researchers] found that calcification of the arteries was the best predictor of heart disease. Those in the highest third of vitamin K2 intakes were 52 percent less likely to develop severe calcification of the arteries, 41 percent less likely to develop heart disease, and 57 percent less likely to die from it.
K2 is preferentially used by other tissues to deposit calcium in appropriate locations, such as in the bones and teeth, and prevent it from depositing in locations where it does not belong, such as the soft tissues.
http://chriskresser.com/vitamin-k2-the-missing-nutrient
The rest of this post is a good read, and I'm sure you are asking "where do I get K2?"

The list:  Natto, hard cheese, soft cheese, egg yolk, butter, chicken liver, salami, chicken breast, ground beef

Kresser continues:  It is important to note that commercial butter is not a significantly high source of vitamin K2. Dr. Weston A. Price, who was the first to elucidate the role of vitamin K2 in human health (though he called it “Activator X” at the time) analyzed over 20,000 samples of butter sent to him from various parts of the world. As mentioned previously in this paper, he found that the Activator X concentration varied 50-fold. Animals grazing on vitamin K-rich cereal grasses, especially wheat grass, and alfalfa in a lush green state of growth produced fat with the highest amounts of Activator X, but the soil in which the pasture was grown also influenced the quality of the butter. It was only the vitamin-rich butter grown in three feet or more of healthy top soil that had such dramatic curing properties when combined with cod liver oil in Dr. Price’s experiments and clinical practice.

Just another example of how a change in life habits - like switching from a hunter gatherer style to that of wheat farming/consumption - can have a significant impact via a nearly invisible mechanism.  I've got to find a way to make the kidneys, heart and liver from harvested wild animals taste/smell good enough to eat.