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Vitamin K is lipid soluble and may therefore be stored in fat. It plays a role in blood clotting and in enhancing the calcium-binding properties of the bones. Vitamin K exists in two natural forms. The majority of vitamin K is produced by microorganisms (bacteria) that synthesize it from food in the intestine. The synthesized vitamin is called menaquinone or vitamin K2. It can also be found in certain foods, like green vegetables, in the form of phytomenadione or vitamin K1 

Roles

What does vitamin K do? 

Vitamin K1 plays a direct role in the blood clotting process while vitamin K2 is active in the calcification of tissues.

  • Vitamin K1:
    • Antihemorrhagic properties.
  • Vitamin K2 (still being studied):
    • Prevention or treatment of osteoporosis;
    • Prevention of heart disease.

Needs

Adequate Intake *(AI) of Vitamin K: 

Age
Vitamin K
µg**
Infants
0 to 6 months
2µg
7 to 12 months
2,5µg
Children
1 to 3 years
30µg
4 to 8 years
55µg
Preteens
9 to 13 years
60µg
Boy teenagers
from 14 to 18 years
75µg
Men
19 and up
120µg
Women
19 and up
90µg

Source: Food and Nutrition Board, Institute of Medicine, USA, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc, 2002. This data reflects a consensus between Canadian and U.S, authorities.

*Lacking sufficient scientific evidence, authorities have established adequate intakes (AIs) rather than recommended dietary allowances (RDAs). Adequate vitamin K intake is based on average intakes in North Americans in good health.

**1 µg = 1 microgram, or 1 millionth of a gram.

Sources

A relatively limited number of foods contribute significantly to phytomenadione intake. Vitamin K is sensitive to light, alkaline conditions, and air, but is not destroyed by cooking heat. 

Food Sources for Vitamin K: 

Foods Rich in Vitamin K1 
Apricots, seaweed, asparagus
Broccoli, carrots, celery
Brussels sprouts, green cabbage, cauliflower
Spinach
Canola oil, soybean oil
Peas, pears, plums, and grapes

Source: DRIs, Dietary reference intakes, 2002, p. 257.

Foods Rich in Vitamin K2
Liver
Cheese
Fish oil
Milk
Miso
Yogurt

Source: DRIs, Dietary reference intakes, 2002, p. 257.

Deficiency

It is extremely rare to observe clinically significant vitamin K deficiency within the population since this vitamin is essentially produced by the body. 

However it may occur in individuals who have: 

  • Intestinal absorption disorders (cystic fibrosis, celiac disease, etc.);
  • Serious liver or bile duct disorders;
  • Taken antibiotics for an extended period (destroying the intestinal flora);
  • An addiction to alcohol.

NOTE: At birth, it takes the body one week to produce vitamin K. Newborns therefore receive a vitamin K supplement at birth to promote clotting in case of bleeding and prevent the risk of hemorrhage. 

Signs of vitamin K deficiency: 

  • Bleeding in the mouth;
  • Urinary tract or genital bleeding;
  • Stomach, intestinal, or skin bleeding;
  • Hematomas (ecchymoses).

Adverse effects

Even at very high doses, vitamin K causes no notable adverse reactions. 

Signs of excess vitamin K: 

  • none. 

Cons-indications

  • Hypersensitivity to vitamin K. 

Interactions

Natural health products or vitamin supplements: 

  • Vitamin K taken at high doses may reduce the anticoagulant effect of certain plants or supplements (garlic, Ginkgo biloba, red clover);
  • Vitamin E taken at high doses reduces the effect of vitamin K;
  • Mineral oil reduces the effect of vitamin K.

Medications:  

Taking vitamin K supplements may reduce the anticoagulant effect of certain medications while vitamin K absorption is decreased by: 

  • Taking antibiotics for an extended period of time;
  • Taking medications that reduce blood lipids;
  • Taking cholesterol medications;
  • Taking anticonvulsive medications.

Additional information

Speak with your pharmacist if you plan to take vitamin K supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take. 

Other names

Vitamin K, Phytomenadione, Vitamin K1, Blood clotting vitamin, Menaquinone , Vitamin K2