Vitamin K2 is emerging as an exciting player in the quest to reduce risk for heart disease. (Also see my previous post, Vitamin K2: Newest heart-healthy supplement?)
If you believe the observations coming from the Rotterdam Heart Study and others that suggest that there is up to 57% less heart attack in people who consume vitamin K2 from diet, how can you go about getting more from the foods you choose?
The Rotterdam Heart Study showed that a threshold intake of 32.7 micrograms of K2 per day, mostly from cheese, yields the reduction in cardiovascular events.
Of all the foods that contain vitamin K, only about 10% of occurs in the K2 form, the other 90% being the more common K1. (K1 is important for regulation of blood clotting and is abundant in green vegetables.)
The ideal source of K2 is natto, an unpalatable, gooey mass made from fermented soybeans that smells of ammonia and is popular among Japanese. Natto is something you might see natto on Andrew Zimmern's Bizarre Foods TV show - I would not recommend it unless you are among the more nutritionally adventurous. In Japan, natto consumption appears to be responsible for decreased osteoporosis and bone fractures, health conditions best studied for K2. But natto's phlegmy consistency makes it virtually inedible to anyone but native Japanese. (I've had it and it is truly awful.)
Vitamin K2 occurs in several forms that differ slightly in structure. The form from natto is MK-7, while other forms, like MK-4 and MK-8,9,10, are found in cheese and, to a lesser degree, meat, eggs (yolks), and dairy products. Some data suggest that you can convert some K1 to MK-4 in your intestinal tract. The MK-4 form of vitamin K2 is short-lived, lasting only 3-4 hours in the body. The MK-7 form, in contrast, lasts several days.
Natto contains 1000 mcg of MK-7, 84 mcg MK-8, and no MK-4 per 3 1/2 oz serving.
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), or roughly 5 mcg per yolk.
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.
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. In my view, factory farm raised meat is a travesty and should be avoided, regardless of K2 content.)
Another interesting fact: Since mammals synthesize a small quantity of Vit K2 from vitamin K1, then eating lots of green vegetables should provide substrate for some quantity of K2 conversion. However, work by vitamin K2 pioneer, Dr. Leon Schurgers at the University of Maastricht, has shown that K1 absorption is poor, no more than 10%, but increases significantly when vegetables are eaten in the presence of oils. Yet another reason to liberally pour olive, canola, or flaxseed oil liberally on your salad and avoid the miserable non-fat and low-fat (high fructose corn syrup products!).
Until we learn more about vitamin K2 for heart health, I believe that it is a good idea to enjoy your gouda, Emmenthaler, Gruyere, and feta cheeses, along with a few egg yolks. Perhaps K2 represents one more reason to rebel against the wrong-headed low-fat dietary mistakes of the past 30 years.