Sources
Dietary Sources of Vitamin K
Vitamin K occurs naturally in two major forms — vitamin K1 and vitamin K2.
In general, vitamin K1 (phylloquinone) is derived from dietary sources
such as leafy green vegetables (spinach, broccoli and kale) and soybean oil, whereas vitamin K2 (the family of menaquinones or MKs) is of bacterial origin.
Green vegetable-rich western diets contain large amounts of vitamin K1. The problem is that vitamin K1 obtained from fresh vegetables is very poorly absorbed. Only about 10-20% of it reaches circulation, and as vitamin K1 has a very short serum half- life only a small amount is able to reach peripheral parts of the body. Moreover, most of vitamin K1 is absorbed by the liver to secure coagulation - with little left for other tissues.
Vitamin K2, and especially Menaquinone-7 (MK-7), is initially transported to the liver, but it is also transported to extrahepatic (non-liver) tissues such as bones and vasculature. This is mainly due to MK-7’s chemical structure which is different from vitamin K1, enabling K2 to be bound to other fat particles in the circulation. MK-7 thus survives longer in the circulation, manifested in vitamin K2’s very long serum half-life.20
Vitamin K2 can also be produced within the human body by beneficial bacteria colonizing the intestines. However the intestinal absorption seems to be minimal, contributing little to the body’s vitamin K requirements especially for bones and arteries. The problem is that bacteria producing vitamin K2 live in the lower part of human gut, where bile salts, required to absorb nutrients from the alimentary canal, are not present.
Therefore, the daily requirement for vitamin K2 has to be supplemented from dietary sources, such as curd, cheeses and other fermented dairy products shown to contain vitamin K2. However, you would need to have an extremely high consumption of these foods in order to get a sufficient amount of vitamin K2. The best source of vitamin K2 is the traditional Japanese dish natto which is rich in vitamin K2 as the long-chain menaquinone-7.21 As natto remains unpopular in the western world, supplementation with additional vitamin K2 is the optimal alternative.
MK-7 is the superior form of vitamin K
All K vitamins are similar in structure, but differ in the length of the “side chain”. The longer the side chain, the better effect and efficiency. Consequently, the long-chain menaquinones (especially MK-7) are the most desirable as they are nearly completely absorbed (body requires smaller doses) and stay in the blood for the longest time. Meaning, vitamin K2 is also available for tissues outside the liver, namely bones, arteries and soft tissues.
There are three forms of K vitamins presently available in dietary supplements; synthetic vitamin K1, synthetic menaquinone-4 (MK-4) and natural vitamin K2 as menaquinone-7 (MK-7). Recent studies show that natural vitamin K2 as MK-7 is consistently found to be much more effective compared to both vitamin K1 and MK-4. This is mainly due to significantly greater bioavailability (well absorbed) and bioactivity (half-life time).