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Vitamin K

Summary

Vitamin K is needed for proper blood clotting and bone health. Vegans who eat leafy green vegetables with some added oil on a daily basis should receive more than adequate vitamin K. Even those who do not might obtain enough vitamin K from intestinal bacteria, unless they have had a significant course of antibiotics. Making sure you get plenty of vitamin K through leafy green vegetables is the best plan.

Vitamin K Requirements and Issues

Vitamin K is a vitamin needed for blood clotting. It also has activity in bones and deficiency can result in bone fractures, especially in old age. The Dietary Reference Intake for vitamin K is 120 µg for men and 90 µg for women. Table 1 shows the vitamin K content of plant foods that are high in vitamin K.

Vitamin K refers to the chemical menadione and any derivatives of it that exhibit anti-hemorrhagic activity in animals fed a vitamin K-deficient diet. There are two types:

• Phylloquinone - found primarily in plant foods; most prevalent in green leafy vegetables. Traditionally called vitamin K1. (1)
• Menaquinone - found in animal tissues and bacteria. Traditionally called vitamin K2. (1)

Table 1. Vitamin K in Plant Foods2
Food	Preparation	Serving	µg
Broccoli	boiled	1/2 cup	110
Kale	shredded,boiled	1/2 cup	531
Spinach	boiled	1/2 cup	442
Collards	boiled	1/2 cup	418
Romaine lettuce	shredded	1 cup	48
Swiss chard	boiled	1/2 cup	286

Because menaquinone is not found in plant foods, some laypeople have suggested you need to eat animal products in order to have adequate vitamin K status. The scientific consensus has been that either of the two types of vitamin K are adequate, especially regarding vitamin K's blood clotting activity. In the United States, enteral nutrition products, which are used for people who cannot eat normally and often provide the only nutrition they receive for months or years, contain phylloquinone for vitamin K (1) and these patients presumably do fine, with regard to blood clotting, with only phylloquinone in their diet.

Additionally, menaquinone is produced by a number of different bacteria species that typically live in the digestive tract of humans (1), and can be absorbed in the distal part of the small intestine (5). Unless someone has had significant antibiotic therapy, they should have plenty of such bacteria providing them with menaquinone. It is difficult to induce vitamin K deficiency (measured by slow blood clotting) by removing vitamin K from the diet, presumably due to the production of vitamin K by intestinal bacteria (1). However, it is possible to induce vitamin K deficiency (slow blood clotting) through antibiotic therapy, indicating intestinal bacteria provide a significant amount of vitamin K (1).

One study measuring blood-clotting in vegetarians (3) and one study measuring blood-clotting in vegans (4) did not show them to have slow blood clotting times. An abnormal rate of blood clotting problems has not been apparent for children raised vegan from birth; it would be unusual for their diets to be supplemented with menaquinone.

It, therefore, seems safe to assume that vegans have no need for menaquinone supplementation; especially when it comes to vitamin K and blood clotting. But what about bone health? Again, apparently healthy vegans are probably getting plenty of menaquinone, if it's even necessary to have in addition to phylloquinone, from gut bacteria.

There is evidence that elderly women can reduce their chance of bone fracture by supplementing with vitamin K, specifically phylloquinone (6). So it appears that phylloquinone is also adequate for bone health and there is no evidence to date that menaquinone is superior. A literature search (May 2010) revealed no studies comparing phylloquinone to menaquinone with regard to bone health.

There is one vegan food that is very high in menaquinone: natto. Natto has 998 mcg of menaquinone per 100 g portion (1).

Fat and Vitamin K Absorption

Vitamin K is a fat-soluble vitamin, and fat can significantly increase its absorption from food (7). Since green leafy vegetables naturally contain very little fat, it is a good idea to add some fat or oil when preparing them.

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References