Friday, November 7, 2008

Cardiovascular Disease and Vitamin K2

Vitamin K2 is intimately involved in calcium metabolism. Matrix Gla-protein (MGP) is a vitamin K-dependent protein that is secreted in cartilage, lung, heart, kidney and arteries. MGP prefers the MK-4 form of vitamin K2, the type that occurs almost exclusively in animal foods. Mice lacking MGP develop extensive arterial and soft tissue calcification (accumulation of calcium, as in bone). Same for humans with naturally occurring mutations in MGP (Keutel syndrome). It also happens in rats treated with warfarin, which inhibits vitamin K recycling. Let's hear what Dr. Cees Vermeer and his group have to say about MGP:
Among the proteins involved in vascular calcium metabolism, the vitamin K-dependent matrix Gla-protein (MGP) plays a dominant role. Although on a molecular level its mechanism of action is not completely understood, it is generally accepted that MGP is a potent inhibitor of arterial calcification. Its pivotal importance for vascular health is demonstrated by the fact that there seems to be no effective alternative mechanism for calcification inhibition in the vasculature. An optimal vitamin K intake is therefore important to maintain the risk and rate of calcification as low as possible.
So why do we care about vessel calcification? It associates strongly with the risk of heart attack and total mortality, better than traditional markers like the Framingham risk index*. That's because it's actually a measure of the disease process, rather than a marker with an unclear connection to it.

In my post on vitamin K2, I mentioned the Rotterdam study, which found that vitamin K2 intake is strongly associated with a lower risk of cardiovascular and total mortality. Vitamin K1, which is the type found in plants, was not associated with reduced mortality. I just came across another study in women selected from the PROSPECT cohort that showed something similar. Women with the highest K2 intake had the lowest level of coronary calcification. There was no association with K1. This suggests, yet again, that humans aren't very good at making the conversion from K1 to K2 MK-4. This is probably because during evolution, we always had a ready source of K2, so efficient conversion became unnecessary. Vitamin K2 MK-4 is found almost exclusively in animal foods.

Notably absent from the main text body is a discussion of where the K2 is coming from. It's tucked away in one sentence of the methods section: "cheese contributed 54%, milk products 22% and meat 15% of menaquinone intake." Oops! These are the foods that are supposed to cause heart disease! And do you remember where the K2 is? In the fat-- double oops! Yet another important nutrient that's found in animal fat.

Keep in mind that these Dutch women have an intake of K2 that is probably lower than what we would have eaten as hunter-gatherers. Most people in modern societies are verifiably K2 deficient. A focus on the organs (brain, pancreas) and fats of wild animals, shellfish, fish eggs and insects would have assured hunter-gatherers a high intake of vitamin K2 MK-4. This is precisely what Weston Price found in Nutrition and Physical Degeneration. He refers to vitamin K2 MK-4 as "activator X" in the book. In modern times, our most readily available source of vitamin K2 MK-4 is actually not a paleolithic food at all, it's butter from pasture-raised cows. It's how we can get away with not eating brain, pancreas and bugs.

*I plugged my numbers into this Framingham risk index calculator and it gave me the message "Please go back and enter an HDL value in the range of 20-100."!! I can imagine if you follow NCEP dietary guidelines your HDL would never break 100 mg/dL!