K1 and K3 are both available as part of multivitamin complexes or alone, in 5 mg tablets. These fat-soluble forms are an excellent source of vitamin K. Water-soluble chlorophyll is the most common form of vitamin K found over the counter. It is available in tablet, capsule, and liquid forms.

What is Vitamin K ?
Vitamin K is a group of 2-methilo-naphthoquinone derivatives. There are three notable forms of vitamin K, K1 (phytonadione, phylloquinone, phytonactone , K2 (menaquinones), which can be formed by natural bacteria in the intestines, and K3 (menadione), the most active synthetic form of the preparations K3-K7. Plants synthesize phylloquinone, also known as vitamin K1. Vitamin K1 or phylloquinone is the principal dietary source of vitamin K and its predominant circulating form. Vitamin K2 is the collective term for a group of vitamin K compounds called menaquinones. The menaquinone homolgues are characterized by the number of isoprene residues comprising the side chain. Vitamin K2 is found in chicken egg yolk, butter, cow liver, certain cheeses and fermented soybean products such as natto. Very little vitamin K is stored by the body; small amounts of this vitamin are deposited in the liver and in the bones, but this amount is only enough to supply the body's needs for a few days.

Vitamin K is involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate residues. These proteins have in common the requirement to be post-translationally modified by carboxylation of glutamic acid residues (forming gamma-carboxyglutamic acid) in order to become biologically active. These proteins include the vitamin K-dependent coagulation factors II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart factor), protein C, protein S, protein Zv and a growth-arrest-specific factor (Gas6). Menadione is a fat-soluble vitamin precursor that is converted into menaquinone in the liver. The primary known function of vitamin K is to assist in the normal clotting of blood, but it may also play a role in normal bone calcificaton. Without vitamin K, the carboxylation does not occur and the proteins that are synthesized are biologically inactive.

Where it is found
Rich sources of vitamin K include broccoli, Brussels sprouts, cabbage, cauliflower, kale, spinach and soybeans. Cooked dark green vegetables, such as spinach, kale and broccoli, can provide more than one RDA in a single serving. Cow milk is also a good source of the vitamin. Asian soy foods also are excellent vitamin K sources. Hydrogenation of vegetable oils may decrease the absorption and biological effect of dietary vitamin K. Phylloquinone (vitamin K1) is the major dietary form of vitamin K. Bacteria that normally colonize the large intestine synthesize menaquinones (vitamin K2), which are an active form of vitamin K.

Possible Side effects / Precautions / Possible Interactions:
There is no known toxicity associated with high doses of phylloquinone (vitamin K1), menaquinone (vitamin K2), or menadione (vitamin K3) and its derivatives. High intake of vitamin K is not recommended for individuals taking anticoagulant medications such as Warfarin (coumadin).

Possible Interaction:
If you are currently being treated with any of the following medications, you should not take vitamin K without first talking to your health care provider.
Antibiotics -- Antibiotics, particularly a class known as cephalosporins, reduce the absorption of vitamin K in the body. Long-term use (more than 10 days) of antibiotics may result in vitamin K deficiency because these drugs kill not only harmful bacteria but also beneficial, vitamin K-activating bacteria. This is not likely to occur in people who already have low levels of vitamin K or are at risk for deficiency (such as those who are malnourished, elderly, or taking warfarin). Cephalosporins include: