Vitamin K has long been known for its role in ensuring blood clots properly which is especially important for proper wound healing. Without its presence, the times for clotting are significantly altered where blood does not clot at all. There is also some association with proper bone growth and supports good cardiovascular health. A deficiency of this vitamin in adults is believed to also lead to heart disease, weakened bones, tooth decay and even some forms of cancer.
Vitamin K is the only fat soluble vitamin with a specific coenzyme function. It was given the K designation because it was short for Koagulation in German.
There are three distinct forms which are K1, K2 and K3.
Known as phylloquinone. It is commonly present in plants and is often isolated from alfalfa leaves. It is distinguished by having a phytyl chain.
Known as menaquinone. This variants is produced by bacteria in the gut and is also found in animals. It is distinguished by the presence of the isoprenyl side chain.
The variant known as menadione and actually a synthetic form. It is entirely water soluble because it lacks any side chain.
We regard all these vitamin derivatives as naphthoquinone derivatives. All three are heat stable but their activity is lost through oxidation, strong acids and alkalies.
Dietary Sources Of Vitamin K
- green leafy vegetables – such as kale, cabbage leaves, broccoli and spinach
- vegetable oils – especially rapeseed oil
- cereal grains – wheat, barley and oats
- small amounts can also be found in meat and dairy foods like cheeses.
How much do I need?
Adults need approximately 1 microgram a day of vitamin K for each kilogram of their body weight. For example, someone who weighs 80kg would need 80micrograms a day of vitamin K, while a person who weighs 65kg would need 65mcg a day. You should be able to get all the vitamin K you need by eating a varied and balanced diet although failing that, a supplement will provide the necessary amounts. Excess vitamin K is stored in the liver which is then used for further use and so like vitamin D, can be used at other times.
The Department of Health (UK) suggest all your vitamin K can be obtained from a varied and balanced diet although they recommend not to take too much otherwise it might be harmful. There is not enough evidence to suggest whether too much of this vitamin is an issue however but check the dosage requirements on any supplements. Taking 1mg or less of vitamin K supplements a day is unlikely to cause any harm.
A range of supplements are available in capsule and tablet form, and as drops. Many will describe the vitamin as K-2 (menaquinone-4) because this particular form is the most active form and is extremely potent and efficacious. We often find alfalfa included in the capsules.
Absorption of the vitamin occurs in the upper small intestine. Vitamins K1 and K2 need bile salts for absorption. They are transported from the mucosal cells to the liver by binding to chlylomicrons. However K3 is easily absorbed without needing bile salts because of its water solubility.
All vitamin K is stored like many nutrients in the liver which makes it a good source for this vitamin. It is also present in the spleen and skeletal muscle.
Vitamin K is transported in the blood stream by binding to beta-lipoproteins (LDL).
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Excellent references on the vitamin can be found on the NHS web-site.