Vitamin K is a substance that plays a key role in helping blood to clot. Without clotting, a person can bleed to death, even after a minor injury. Vitamin K also plays an important role in helping bones develop normal structure.

Vitamin K deficiency resulting from dietary factors is rare. However, deficiency may develop when conditions such as bile-production failure prevent proper fat absorption of the vitamin. Use of certain drugs also can prevent proper absorption of vitamin K. A deficiency can lead to failure of the blood to clot and tendency to bruise easily.

Excessive intake of vitamin K does not appear to cause illness or symptoms on its own. However, people who take anticoagulants need to avoid eating excessive amounts of food rich in vitamin K because the vitamin can prevent the drug from working properly. 

Bacteria in the body’s intestines produce about half of the body’s needed vitamin K. The rest must come from dietary sources. The best sources include:

• Green, leafy vegetables (e.g., spinach)
• Other cruciferous vegetables (e.g., broccoli, cauliflower)
• Liver

Vitamin K is also available in supplement form. People who have bruising and bleeding disorders may benefit from taking supplements. Supplements also may be recommended for women who are at risk of osteoporosis. However, people should not take vitamin K supplements without first consulting a physician.

Vitamin K is a fat soluble substance that plays a key role in helping blood to clot. This is the action that takes place when cells in the blood act like glue and stick together at the surface of a cut. Clotting is necessary following an injury that causes bleeding. Without clotting, a person easily can bleed to death. Clotting, or coagulation, is the end of a complex process involving numerous proteins, enzymes and vitamin K.

There are three forms of vitamin K:

• Phylloquinone (K1). Found in plant sources of food, including oils.
  
  
• Menaquinone (K2). Produced by the body and by animal sources of vitamin K (e.g., liver, egg yolks).
  
  
• Menadione (K3). Manufactured, or "synthetic," form.
  

The Food and Nutrition Board of the National Academy of Sciences has issued the following adequate intakes (AIs) for vitamin K. The figures are expressed in micrograms (mcg):

For years, it has been believed that most Americans get enough vitamin K through their diets to meet these recommendations. However, recent studies have brought this belief into question. In particular, surveys have indicated that children and young adults may not be getting as much vitamin K from their diets as they should.

fat soluble vitamins such as vitamin K can be stored in the liver and the fatty tissues of the body. However, the body stores very little vitamin K. Deficiency may develop when conditions such as bile-production failure prevent proper fat absorption of the vitamin. Use of certain drugs also can prevent proper absorption of vitamin K. For example, prolonged use of antibiotics can lead to destruction of the bacteria in intestines that create vitamin K. Meanwhile, use of anticoagulant drugs can prevent proper absorption of vitamin K.

Various diseases can lead to vitamin K deficiency, including cystic fibrosis, celiac disease, Crohn’s disease and liver disease. Other causes of vitamin K deficiency include:

• Ingesting too much mineral oil
  
  
• Ongoing diarrhea
  
  
• Long-term use of total parenteral nutrition (TPN), which is nutrition provided intravenously
  
  
• Ongoing hemodialysis
  
  
• Serious burns

Elderly individuals may also be at an increased risk of vitamin K deficiency. Many older people take many medications, eat inadequate amounts of vegetables and may have bacterial overgrowth which impacts the production of vitamin K in the gut.

People with a deficiency of vitamin K may have blood that does not properly coagulate. Deficiency also may lead to easy bruising. 

Excessive intake of vitamin K does not appear to cause illness or symptoms on its own. However, people who take anticoagulants need to avoid eating excessive amounts of foods rich in vitamin K because the vitamin can prevent these drugs from working properly.

Vitamin K’s most important role is in helping the blood to clot following an injury. Vitamin K is involved in activating six of the 13 proteins that cause blood to clot following an injury. This prevents a person from bleeding to death.

It also helps the body to synthesize other proteins for the kidneys, blood and bones and plays an important role in helping bones develop normal structure. Without enough vitamin K, bone produces a protein that is unable to bind with the minerals that normally help form bone. As a result, bone density is low, which raises the risk of the bone-thinning disease known as osteoporosis.

Vitamin K supplements also may be used to reduce the risk of bleeding in liver disease and malabsorption syndromes. Women who experience heavy menstrual bleeding may be treated with vitamin K. Other conditions that may be treated with vitamin K include:

• Osteoporosis. Research indicates that vitamin K supplements strengthen bones and reduce the risk of fractures, particularly in post-menopausal women.
  
  
• Cystic fibrosis. People with this condition often have vitamin K deficiency and may benefit from taking supplements.  Vitamin K deficiency in individuals with cystic fibrosis is worsened by their recurrent need for antibiotics, which can lead to destruction of the bacteria in intestines that create vitamin K.
  
  
• Kidney stones. Vitamin K supplements may help prevent formation of kidney stones.  Vegetarians, who tend to have a high vitamin K intake, usually have a low incidence of kidney stones.
  
  
• Body odor. Vitamin K is available in plant foods in a water-soluble source known as chlorophyll, which is sometimes used to control body, fecal and urinary odor.
  
  
• Skin wounds. Water-soluble forms of vitamin K may be used to treat skin wounds.
  
  
• Snake bites. Some snake venoms destroy vitamin K, putting a person at risk for bleeding to death. An injection of vitamin K can arrest this process.

Despite the potential benefits, taking supplements is not without risk. Some people may experience side effects, and vitamin K supplements may interact poorly with some medications. As a result, people are urged not to take vitamin K or any other supplement without first consulting a physician.

Bacteria in the body’s intestines can produce vitamin K on their own. This vitamin K is stored in the liver. However, newborn infants are born with a sterile intestinal tract that does not begin to produce these bacteria for several weeks. As a result, newborns typically receive a shot of vitamin K to ensure that they are not deficient in this vitamin. In the past, there were some concerns that these shots might cause cancer. However, research has not found this to be true.  

The amount of vitamin K produced by bacteria in the body accounts for about one-half of a person’s needs. The rest must come from dietary sources. The best sources include green, leafy vegetables (e.g., spinach), liver, and members of the cabbage (e.g., broccoli, cauliflower) family.

Other dietary sources of vitamin K include:

• Cereal
• Eggs
• Fruits
• Meat
• Milk and other dairy products
• Other vegetables
• Some unsaturated oils, especially from fish

Examples of certain foods and the amount of vitamin K (in micrograms) they contain include:

Freezing foods may destroy vitamin K; however, heating does not affect it.

Vitamin K is also available in supplement form. People who have bruising and bleeding disorders may benefit from taking supplements. Supplements also may be recommended for women who are at risk of osteoporosis. Studies have shown that women who take vitamin K supplements are less at risk for hip fractures, a major complication associated with osteoporosis.

People should not take vitamin K supplements without first consulting a physician. These supplements can cause health problems when used by certain populations. For example, women who are pregnant and take these supplements may cause jaundice in their children. People with certain health conditions also may be poor candidates for using supplements. Such conditions include:

• Chronic diarrhea
• Gallbladder disease
• Intestinal problems
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency
• liver disease
  Cystic fibrosis or other diseases affecting the pancreas

Preparing questions in advance can help patients have more meaningful discussions with health professionals regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions related to vitamin K:

1. How will I know if I am getting too little or too much vitamin K?
   
   
2. Will I be aware of vitamin K deficiency before the situation is potentially dangerous (e.g., excessive bleeding following an injury)?
   
   
3. Who can I talk to about planning a diet with an appropriate amount of vitamin K?
   
   
4. What foods do you suggest I eat to increase my intake of vitamin K?
   
   
5. Do you advise taking vitamin K supplements?
   
   
6. What type of supplement do you recommend?
   
   
7. What are the risks or side effects associated with this supplement?
   
   
8. Should I take this supplement with food?
   
   
9. I am taking anticoagulants. Do I have to change my diet?
   
   
10. Can I be certain my newborn gets enough vitamin K from breastfeeding?
    
    
11. How can I make sure my child is getting enough vitamin K in school meals?