Vitamin K – Benefits, Sources, Deficiencies, Tips

Vitamin k

In classical medicine, high doses of vitamin K are used to counter the harmful effects of an overdose of warfarin (an anticoagulant) or a failure in blood clotting.

Also read : Vitamins : Functions and resources

Description of vitamin K

The vitamin k is a fat-soluble vitamin (soluble in fat). Its name comes from German Koagulation, an allusion to the role it plays in blood clotting. There are two main forms of this vitamin: phytomenadione, or vitamin K1, which comes mainly from green vegetables, and menaquinone, or vitamin K2, which is produced by bacteria in the colon or which appears in certain foods as a result of a fermentation process (cheese, miso, natto, etc.). Vitamin K1 is more directly involved in the coagulation process, while K2 acts more on the calcification of soft tissue.

In North America, as in most European countries, vitamin K1 is found in the form of medication, from supplements or in multivitamin supplements. For only a decade, we have been interested in vitamin K2 and the role it can play in the prevention or even the treatment of osteoporosis or in preventing cardiovascular disorders.

There is a synthetic form, the vitamin K3 (or menadione), which is no longer used in North America because it has been linked to liver toxicity. It is now limited to veterinary use.

Vitamin K history

The vitamin K1 was first isolated from alfalfa. Two biochemists, the Danish Henrik Carl Peter Dam and the American Edward Adelbert Doisy, shared the Nobel Prize in medicine or physiology in 1943 for their discoveries on vitamin K, a clotting factor.

The vitamin K2 was then found in a fermented fish meal. We have also discovered that our own colon produces this same molecule when its intestinal flora is healthy and abundant.

Japanese researchers have developed a natto (pressed and fermented soy beans) called “functional”. This product is made by fermenting soybeans with a strain of bacteria specially selected for its ability to produce good amounts of vitamin K2. Within a program relating to foods for specific medicinal use (FOSHU – Food for Specific Health Use), implemented by the Japanese Ministry of Health, we do not hesitate to assert that this natto can help prevent the osteoporosis. In Japan, a particular form of vitamin K2 (MK-4) is a recognized treatment for osteoporosis.

Since October 2005, vitamin K supplements have been available over the counter in Canada, provided that the recommended daily dosage does not exceed 120 µg per day.

Vitamin K : research and identified benefits


Most epidemiological studies indicate that the deficiency in vitamin k is associated with reduced bone density and an increased risk of fractures in people over 60 and postmenopausal women.
In 2003 and 2004, two studies of postmenopausal women showed that vitamin D and calcium supplements increased bone density or slowed down more markedly if they were combined with vitamin K1. These results were contradicted in 2008 by other researchers, who noted, however, an improvement in the indices of bone demineralization.
According to a large study published in 2008, vitamin K1 does not prevent the decline in bone density linked to age. However, it would significantly reduce the possibility of fractures in women with osteopenia.

With regard to vitamin K2, studies and meta-analyzes show that a high dose of this vitamin (45 mg per day), absorbed alone or with vitamin D3 or calcium, can increase or preserve bone density in postmenopausal women. It also reduces the risk of fractures in people who have vitamin K deficiency or have osteoporosis.

Most of the studies have been done in Japan. Japanese women generally have lower bone density than their western counterparts, but paradoxically, they have fewer hip fractures. The reasons, which could be socio-cultural, anatomical, genetic, are not known at this time. Still, several researchers believe that the effects of vitamin K are not fully extrapolated to Western women. This would explain, for example, that a study carried out in Denmark does not observe a relationship between nutritional intake of vitamin K and bone density or the incidence of fractures24. Although the results require confirmation by tests carried out with Westerners, all the authors agree, however, to stress the importance of a high food intake of vitamin K in the maintenance of bone health.

In addition, among the trials conducted in Japan, 4 involved a total of 120 subjects who took prednisolone (a corticosteroid): Vitamin K2 (45 mg daily), taken alone or with vitamin D, has been shown to reduce bone demineralization caused by this medication.

Cardiovascular protection

Vitamin K could play a protective role against atherosclerosis and cardiovascular disease. Indeed, a link has been established between vitamin K deficiency and an increased risk of arterial calcification. Researchers have also shown that taking vitamin K1 supplements slows the progression of this calcification or reduces the loss of elasticity in the arteries. Finally, women with osteoporosis after menopause have a higher risk of developing atherosclerosis.

The dosage of Vitamin K

There is insufficient data to suggest a therapeutic dosage. In some studies on Western subjects, 200 µg to 1,000 µg (1 mg) of vitamin K1 has been used per day. In trials in Japan, 45 mg of vitamin K2 was given daily, which is a very high dose.

Sufficient intake* in vitamin K

Age µg**/day
0 to 6 months 2
7 to 12 months 2.5
1 to 3 years 30
from 4 to 8 years old 55
9 to 13 years old 60
14 to 18 years old 75
Men 120
Women 90

Source: Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2002). Food and Nutrition Board, Institute of Medicine, USA. These data are the result of a consensus between Canadian and American authorities.
* In the absence of sufficient scientific data, the authorities have fixed, not a recommended nutritional intake (ANR), but an adequate intake (AS). Adequate vitamin K intake is based on average intakes among healthy North Americans.
** 1 µg = 1 microgram, i.e. 1 millionth of a gram.


Food sources of vitamin K

Vitamin K1: green vegetables (especially darker ones, such as spinach, broccoli and asparagus), seaweed and, to a lesser extent, soybean (9 µg per tablespoon) and canola (6 µg per tablespoon) oils soup). For example, a cup of cooked broccoli (200 g) provides 220 µg of vitamin K1 and a cup of cooked spinach (200 g), 888 µg2. Cooking does not destroy vitamin K.

Vitamin K2: Vitamin K2 is found in miso (fermented soy bean paste), liver, milk, cheese, yogurt and fish oils.

Vitamin K deficiency

Common in newborns, the vitamin K deficiency is treated with supplementation. Rare in adults, a deficiency can nevertheless appear in case of serious liver, bile duct or intestinal disease, which then requires drug treatment. In fact, a vitamin K deficiency leads to a blood clotting failure (hypoprothrombinemia).

Epidemiological studies (see the Research section) indicate that the lower the vitamin K intake, the higher the risk of fractures, suggesting that vitamin K deficiency, even when asymptomatic, could speed up osteoporosis.




  • People taking warfarin are generally recommended to avoid changing their vitamin K intake (food or supplements) in a pronounced way, in order to ensure the stability of the effect of this anticoagulant drug.
  • Vitamin K absorption can be hindered by alcoholism and the use of mineral oil (paraffin oil or petrolatum).


  • Hypersensitivity to vitamin K

Undesirable effect

  • Even at very high doses absorbed for one or two years, vitamin K did not cause any noticeable side effects.


With plants or supplements

  • Taking large doses of vitamin K can in theory reduce the anticoagulant effect of certain plants or supplements (garlic, ginkgo, red clover, for example).
  • Large doses of vitamin E could counter the effect of vitamin K.

With medication

  • Taking vitamin K supplements can reduce the effect of blood thinning medications (warfarin, Coumadin®).
  • Antibiotic treatments (because they destroy the intestinal flora), drugs, such as cholestyramine, cholestipol (treatment of high cholesterol), orlistat (treatment of obesity), certain anticonvulsants like phenytoin (Dilantin ®), carbamazepine and phenobarbital, may slow the absorption of vitamin K.

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