Vitamin K is a fat soluble vitamin, best known for its role in blood clotting and bone health.
The main forms of dietary Vitamin K are two: K1 (phylloquinone) and K2 (menaquinone). K1 is synthesized by plants and its bioavailability is not nearly as good in humans as the K2 form (1). K 2 is the form we get from animal products and is the form we are interested in.
Vitamin K2 is found in animals products like meat, eggs, organs, a Japanese dish called natto, and a high amount is also found in high fat dairy products like butter, cream and cheese. These foods contain more K2 if the animals are grass-fed. Vitamin K2 is also produced by bacteria in the gut. Newborn infants have sterile guts, and are sometimes administered Vitamin K during the first few days after birth, before their intestine gets colonized. The plant form, K1, is found in green leafy vegetables along with some types of fruit.
How it works
Vitamin K functions at the cellular level by catalyzing carboxylation of the amino acid glutamate in certain proteins. These carboxylated glutamate amino acids are called Gla residues. What this basically means, is that Vitamin K alters the structure and function of a few specific proteins, after they have been made.
The main function of those proteins who are altered by Vitamin K is binding calcium, and they are therefore intimately involved in calcium metabolism. The regulation of some of these proteins is modified by Vitamin D and the two vitamins may therefore have a synergistic effect in many cases.
The fact that these proteins function mainly by binding calcium has some important implications:
– First, calcium tends to be removed from the bones, causing reduced bone density and fractures. Research shows that Vitamin K supplementation reduces incidence of bone loss and fractures (2).
– Second, calcium tends to be deposited in the arteries, producing arterial calcification and contributing to heart disease, the world’s nr.1 killer. Research shows that Vitamin K inhibits arterial calcification (3).
There’s evidence that Vitamin K can lessen chances of advanced prostate cancer, the most common cancer in men (4). Vitamin K also reduced recurrence of liver cancer in patients after their treatment (5).
Official requirements are viewed as the amount the liver needs to synthesize necessary blood clotting factors, and therefore deficiency is very rare as the intestinal bacteria produce enough. If viewed from the standpoint of preventing arterial calcification, the requirements may be much higher (6).
In the U.S, the Adequate Intake of either K1 or K2 is listed at 120 mcg/day. However, a study found that 1000 mcg/day was necessary to maximize amount of functional osteocalcin (7), which is one of the main proteins altered by Vitamin K and is highly involved in bone metabolism. The K2 form is much better absorbed, so the required amount of it should be lower.
What to do about it
If you eat a lot of animal food and little gluten grains (which interfere with fat soluble vitamin absorption), then you probably don’t need to supplement. Especially if you eat a lot of high-fat dairy, preferably grass-fed. If your diet is more of a conventional western diet, or if you have arterial calcification, then you might want to consider supplementation.
If you are using anticoagulant medication like warfarin then you should talk to your doctor before increasing your intake of vitamin K, because this vitamin has a large effect on these medications. In fact, blocking Vitamin K function in the cells is the primary mechanism in these kinds of drugs. The problem is that they also tend to block the function of other Vitamin K dependent proteins that are not related to blood clotting.
Humans consumed much more K2 than today in pre-agricultural times, because of their high intake of whole foods and grass-fed, wild animals. One of the shortcomings of the strict paleo diet, in my opinion, is its exclusion of high-fat dairy products, but these are the main sources of Vitamin K2 in our diet today. In fact, people eating the most high-fat dairy products had a whopping 69% lower chance of dying from heart disease than those eating the least (8).
For more information on Vitamin K2, visit Dr. Stephan Guyenet’s Whole Health Source. A lot of what I know about Vitamin K and other fat soluble vitamins I learned from his site, and I found some of these researches there as well.