Vitamin K (Phylloquinone / Menaquinone)

What is Vitamin K?

Vitamin K is a fat soluble vitamin and is available in two natural forms vitamin K1 (phylloquinone or phytomenadione) and vitamin K2 (menaquinones). Fat-soluble vitamins do not dissolve in water and are stored in fatty tissues and the liver which the body can use when needed.

Vitamin K2 is available in various subtypes. Vitamin K1 is the natural form found in plant source, dairy products and vegetable oils. In the human body K1 is converted into K2 through intestinal bacteria and can be found in animal food sources and in some fermented food.

Vitamin K serves an important role in the activation of proteins required for the production of prothrombin required for blood clotting and promotes cardiovascular health. In addition to other key nutrients vitamin K also helps strengthen bone health.

First known use of vitamin K is around in the year 1935. The letter K of vitamin K comes from the Norwegian ‘koagulasjonand, German ‘koagulation’, and the Danish and Swedish word ‘koagulation’.

Health benefits of Vitamin K

Essential for blood clotting factors

Blood clotting which is also known as coagulation is an essential process in the human body and is needed to help prevent excessive bleeding. Vitamin K is needed for various coagulation factors to help with the process and proteins such as fibrinogen involved in the coagulation process rely on vitamin K. When vitamin K is excessively low it can lead to severe bleeding. However, people with blood clotting disorders need to avoid taking too much vitamin K such as those at risk of stroke and on warfarin treatment (anticoagulation). Warfarin is a powerful blood thinner and when patients are on this medication they need to limit foods containing vitamin K to prevent its counteractive effect against treatment.

In simple terms when you get a cut or wound which later turns into a scab through the healing process this is where you are witnessing vitamin Ks blood clotting factors. Platelets which are blood cells involved in the blood clotting process gather up to prevent blood flow. In addition to vitamin K, the protein fibrinogen, calcium also helps the platelets form a clot.

In a calcium deficient state where vitamin K is also low the blood clotting will take much longer. If deficiency is severe in any injuries involving bleeding may cause the person to bleed to death.

Promotes bone health

Vitamin K works synergistically with other nutrients to help strengthen bone health and maintain bone density. In addition to vitamin K, vitamin D also acts as a co factor for maintaining bone health and a combination can help reduce the risk of fractures and other bone related disorders.

Vitamin D works synergistically with calcium to help strengthen bone mineral health.

Vitamin K promotes calcium deposits in the bones and effectively reducing calcium deposits in blood vessels reducing the risk of artherosclerosis. Sufficient vitamin K can help with problems associated with high levels of vitamin D.

Calcium is one of the key essential nutrient necessary for the development and growth of a healthy child into a healthy adult. It is most abundantly found in the bones and teeth. Calcium is required by the body to prevent bone loss. Calcium deficiencies as well as other key nutrients such as magnesium and vitamin D can lead to various bone disorders such as osteoporosis which can be especially found in elderly people and also women going through menopause. In these cases calcium being deposited in bones through adequate K intake can help address the deficiency and maintain bone density.

Some studies are showing low levels of vitamin K1 and K2 increase risk of bone fractures. [1] [2]

Promotes cardiovascular health

Vitamin K can help protect the heart health through its role in activating a protein that helps prevent calcium deposits in the arteries and instead depositing the mineral into the bones. A deficiency of this vitamin is associated with atherosclerosis which can lead to cardiovascular disease. In Vitamin K also helps improves blood pressure possibly through its action of keeping arteries clear and unclogged. [3] [4] [5] [6] [7] [8]

Improves insulin levels

Vitamin K has shown to improve insulin sensitivity and help with glucose metabolism. Some studies are showing the potential of vitamin K reducing risk of type 2 diabetes. [9]

Prevents cancer

Some studies are showing that vitamin K may be potentially effective against cancer.

One study found the growth of cancer cells reduced in people with lung cancer. Another study has shown positive results in treating leukemia. [10]  [11]

Vitamin K2 has also shown that men taking the highest amounts of K2 had a reduced risk of prostate cancer by up to 50% suggesting that vitamin K may protect against prostrate cancer. [12]

The role vitamin K plays in cancer and how it may prevent cancer is still unknown requiring more research.

Agonist / Synergist

Vitamins: A, B3, B5, B6, C, D, E

Minerals: Ca, Cu, Mn

Other: Fat, bile, pancreatic juices, flavonoids, estrogen

Vitamin D and vitamin K are dose dependant cofactors. At normal levels they work synergistically but antagonistic with higher levels.

Vitamin K and D help with calcium metabolism [13]

Vitamin K counteracts harmful effects of high levels of vitamin D

Vtamin K and calcium help to improve bone health and reduce the risk of calcium associated health problems such as calcification of blood vessels. [14]

Vitamin K works with boron to increase estrogen production. Vitamin K and estradiol has shown to prevent the development of arteriosclerosis associated with diabetes. [15]

Vitamin K2 helps with estrogen metabolism. [16]

Supplemental bile salts help with vitamin K absorption and is recommended if bile secretion is low.


Vitamins: A, E

Other: Anticoagulants (Warfarin), mineral oil, oxalates, alcohol, coenzyme Q10, antibiotics

Vitamin A toxicity prevents production of vitamin K2 by intestinal bacteria. [17]

Vitamin A inhibits intestinal absorption of vitamin K as they both share the same pathway and compete for absorbption.

Vitamin D inhibits intestinal absorption of vitamin K.

Vitamin E increases xenobiotic pathways that increase hepatic metabolism and excretion of all vitamin K forms [18]

Vitamin E can also inhibit the intestinal absorption of vitamin K as both fat soluble vitamins share the same pathway. [19]

Vitamin K can inhibit the effects of anticoagulant drug warfarin and people on this medication need to limit dietary intake of vitamin K.

Food sources of Vitamin K

Different forms of vitamin K can be found in different types of food. Vitamin K1 is the most readily available form of vitamin K found in food sources. Vitamin K1 can be found in most vegetable sources which includes kale, cabbage, collard greens, spinach, turnip greens, broccoli, brussels sprouts, turnip greens, mustard greens, green leaf lettuce, alfalfa, green onions (spring onions, chives), tomatoes, and green tea. Some dairy products, grains such as oats and blackstrap molasses also contain vitamin K1.

Vitamin K2 can be found in animal food sources and fermented soybeans. There are several types of vitamin K2 which includes the subtypes ranging between MK-4 and MK-15.

MK-4 which is not synthesised by bacteria can be found in some animal-based food source which includes egg yolks, liver, meat, fish liver oils, butter and chicken.

MK-5 through MK-15 are forms of vitamin K2 produced by intestinal bacteria and commonly found in fermented foods such as Natto. Natto is a traditional Japanese fermented food made from soybean and contains the MK-7 subtype of vitamin K. Most supplements of vitamin K2 MK-7 are sourced from natto.

Vitamin K2 subtypes MK-8 and MK-9 can be found in hard and soft cheeses.

Vitamin K is also synthesised in the body by intestinal bacteria.

Recommended Dietary Allowance

The amounts recommended for vitamins and minerals are different for each country which can be found on the government website of host country. The nutritional data for each country are based on scientific research which are presented by the scientific academies in each country to help advise governmental departments for food and human nutrition.

Below is a list of some of the countries and the EU for which nutritional guidelines are available found on corresponding official government website (including the national academy of science website for the USA).


The  2015–2020 Dietary Guidelines for Americans -  Dietary Reference Intakes

Recommended Dietary Allowances and Adequate Intakes from Food and Nutrition Board, Institute of Medicine, National Academies

Dietary Reference Intakes (DRIs) Food and Nutrition Board, Institute of Medicine, National Academies

Dietary Reference Intakes (DRIs): Tolerable Upper Intake Levels (UL)


Dietary Reference Intakes includes Tolerable Upper Intake Levels


Nutrition Requirements

Safe Upper Levels (SULs) for Vitamins and Minerals

Australia and New Zealand

Nutrient Reference Values (NRVs) and Upper Level Intake 


Dietary Reference Values for nutrients

Tolerable Upper Intake Levels For Vitamins and Minerals

Vitamin K Supplementation

Vitamin K is available as tablets, capsules, liquid and can also be found in multivitamin formulas such as those promoting bone health.

Fat-soluble vitamins should be taken with meals containing healthy fats to help with absorption.

Some studies are showing that vitamin K1 may absorb less than 10% found in plant-based foods. However, this may not be an absorption issue and potentially due to impaired liver function and natural intestinal bacteria may be limited to help convert vitamin K1 into K2 which the liver can then utilize. K2 forms may be better absorbed as this form also remains in the blood for a longer duration than K1. [22] [23]

Some studies are showing the beneficial effects of vitamin K depositing calcium into the bones and reducing risk of arteriosclerosis are from the K2 vitamin. [24] [25]

For better absorption vitamin K supplements should be taken with foods containing fats.

K1 supplements can be derived from alfalfa or made synthetically. The common source of K2 supplement is usually derived from natto and can be identified on supplement labels as the MK-7 subtype.

Take yogurt occasionally to assist production. In a healthy person supplementing with vitamin K may be unnecessary since intestinal bacteria can produce it naturally. Also because it is a fat soluble vitamin the body is able to store about a week's worth of the nutrient for future use.

Deficiency symptoms of Vitamin K

Signs and symptoms of vitamin K deficiency include:

  • Easy bruising
  • Heavy menstrual periods
  • Gum bleeding
  • Nose bleeding
  • Bleeding within digestive tract
  • Blood in urine (Hematuria)
  • Blood in stool
  • Excessive bleeding from cuts or wounds
  • Excessive bleeding from puncture sites or incisions (from surgery or injections)
  • Impaired clotting
  • Prolonged blood clotting time
  • Decreased levels of prothrombin
  • Increased prothrombin time (PT)
  • Behavioral problems
  • Osteoporosis
  • Cardiovascular disease
  • Stroke
  • Calcification
  • Impaired growth and development in infants

The following are some of the causes of a vitamin K deficiency:

  • Inadequate intake
  • Fat malabsorption(due to coeliac disease, cystic fibrosis, pancreatitis or Crohns disease)
  • Medications (Antibiotics, antacids, Anticoagulants (warfarin, coumarin) and anticonvulsants)
  • Malnutrition (in those with chronic conditions such as cancer)
  • Liver disease (bile duct obstruction or primary biliary cirrhosis)
  • Reduced production in the intestines
  • Poor diet
  • Alcoholism (damages liver function)
  • High salicylates intake (Aspirin)
  • High vitamin E intake

Deficiency of vitamin K is uncommon in healthy adults as vitamin is available in most food sources. However a deficiency is common in newborn children and can cause hemorrhagic disease. This occurs more commonly in breastfed infants due to a lack of the nutrient in breastmilk. Cow’s milk in comparison to human breast milk contain more vitamin K. Breast milk contains approximately 2.5 mcg per litre and cow’s milk containing 5000 mcg per liter. Vitamin K deficiency can lead to infant morbidity and mortality. The risk of hemorrhagic disease in the newborn increases if the mothers has taken certain medications such as anticoagulants or anticonvulsants or antibiotics.

Vitamin K deficiency is usually not tested for in a blood test and a diagnosis is made through the prothrombin time (PT) test if it is suspected through symptoms of excessive bleeding or easy bruising. Deficiency is identified if prothrombin time is prolonged from which INR (International Normalised Ratio) value is determined. If results indicate low levels of vitamin K, the nutrient is supplied through supplements or injections until INR results are at a normal level. This is determined through the INR results. The normal INR for healthy people is 1.1 or lower.

In healthy people an INR level of 1.1 or less is normal. An INR range of 2.0 to 3.0 is the general marker for using in therapeutic treatments such as patients on anticoagulation treatment with warfarin to prevent the risk of stroke, cardiovascular disease, or treat deep vein thrombrosis.

Toxicity symptoms of Vitamin K

The fat-soluble vitamins A, D, E, and K do not need to be taken daily and in extremely high doses. Fat soluble vitamins have the potential to accumulate toxic amounts in the body as they are not as rapidly excreted like water soluble vitamins.

Vitamin K1 (phylloquinone) and vitamin K2 has not shown to be toxic when taken in high doses. Menadione (Vitamin K3) is a synthetic vitamin K precursor which has shown to cause toxicity and is no longer used to treat vitamin K deficiency.

Some of the known effects of vitamin K toxicity symptoms have been found in infants which includes:

  • Jaundice
  • Hyperbilirubinemia
  • Anemia (Hemolytic)
  • Skin rash
  • Liver damage
  • Stomach upset
  • Brain damage

High doses of vitamin K can interfere with warfarin (coumadin) medication. Warfarin works by inhibiting coagulation process and requires the careful monitoring of INR values to assure it is kept within the therapeutic range. Too much warfarin increases risk of bleeding and if warfarin is made ineffective due to high vitamin K this can reduce warfarins blood thinning properties causing blood clots which can cause serious risk to people with these particular health conditions. People on anticoagulants or recommended to avoid foods too high in vitamin K.

High amounts of vitamin K can cause complications for those with kidney disease receiving dialysis treatment.

Precautions and warnings

Vitamin K may interact with certain medications such as warfarin medication. It is important to seek medical guidance from a health physician before supplementing with vitamin K.