For some reason, my December, 2007, Heart Scan Blog post, Food sources of vitamin K2, has been receiving a lot of traffic.
I therefore reprint the vitamin K2 post below.
Vitamin K2 is emerging as an exciting player in the control and possible regression of coronary atherosclerotic plaque. Only about 10% of dietary vitamin K intake is in the K2 form, the other 90% being the more common K1.
The ideal source of K2 is natto, the unpalatable, gooey, slimy mass of fermented soybeans that Japanese eat and has been held responsible for substantial decreases in osteoporosis and bone fractures of aging. Natto has an ammonia-like bouquet, in addition to its phlegmy consistency that makes it virtually inedible to anyone but native Japanese.
I say that the conversation on vitamin K2 is emerging because of a number of uncertainties: What form of vitamin K2 is best (so-called MK-4 vs. MK7 vs. MK-9, all of which vary in structure and duration of action in human blood)? What dose is required for bone benefits vs. other benefits outside of bone health? Why would humans have developed a need for a nutrient that is created through fermentation with only small quantities in meats and other non-fermented foods?
Much of the developing research on vit K2 is coming from the laboratories of Drs. Vermeer, Geleijnse, and Schurgers at the University of Maastricht in the Netherlands, along with several laboratories in Japan, the champions of K2.
MK-7 and MK-8,9,10 come from bacterial fermentation, whether in natto, cheese, or in your intestinal tract; MK-4 is naturally synthesized by animals from vitamin K1. While natto is the richest source of the MK-7 form, egg yolks and fermented cheeses are the richest sources of the MK-4 form.
Chicken contains about 8 mcg MK-4 per 3 1/2 oz serving; beef contains about 1 mcg. Egg yolks contain 31 mcg MK-4 per 3 1/2 oz serving (app. 6 raw yolks). Hard cheeses contain about 5 mcg MK-4 per 3 1/2 oz serving, about 70 mcg of MK-8,9; soft cheeses contain about 30% less. Natto contains about 1000 mcg of MK-7, 84 mcg MK-8, and no MK-4 per 3 1/2 oz serving.
Thanks to the research efforts of the Dutch and Japanese groups, several phenomena surrounding vitamin K2 are clear, even well-established fact:
--Vitamin K2 supplementation (via frequent natto consumption or pharmaceutical doses of K2) substantially improves bone health. While K2 by itself exerts significant bone density/strength increasing properties in dozens of studies, when combined with other bone health-promoting agents (e.g., vitamin D3, prescription drugs like Fosamax and calcitonin), an exaggerated synergy of bone health-promoting effects develop.
--The MK-4 form of vitamin K2 is short-lived, lasting only 3-4 hours in the body. The MK-7 form, in contrast, the form in natto, lasts several days. MK-7 and MK-8-10 are extremely well absorbed, virtually complete.
--Bone health benefits have been shown for both the MK-7 and MK-4 forms.
--Coumadin (warfarin) blocks all forms of vitamin K.
Interestingly, farm-raised meats and eggs do not differ from factory farm-raised foods in K2 content. (But please do not regard this as an endorsement of factory farm foods.)
Another interesting fact: Since mammals synthesize a small quantity of Vit K2 forms from vitamin K1, then eating lots of green vegetables should provide substrate for some quantity of K2 conversion. However, work by Schurgers et al have shown that K1 absorption is poor, no more than 10%, but increases significantly when vegetables are eaten in the presence of oils. (Thus arguing that oils are meant to be part of the human diet. Does your olive oil or oil-based salad dressing represent fulfillment of some subconscious biologic imperative?)
If we believe the data of the Rotterdam Heart Study, then a threshold of 32.7 micrograms of K2 from cheese yields the reduction in cardiovascular events and aortic calcification.
It's all very, very interesting. My prediction is that abnormal (pathologic) calcium deposition will prove to be a basic process that parallels atherosclerotic plaque growth, and that manipulation of phenomena that impact on calcium depostion also impact on atherosclerotic plaque growth. Vitamins D3 and K2 provide potential potent means of at least partially normalizing these processes.
As the data matures, I am going to enjoy my gouda, Emmenthaler, Gruyere, and feta cheeses, along with a few egg yolks. I'm going to be certain to include healthy oils like olive and canola with my vegetables.