Vitamin K

Vitamin K is a group of fat-soluble vitamins that play a crucial role in blood clotting, bone health, and other essential bodily functions. The vitamin K family includes two naturally occurring forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). Vitamin K1 is primarily found in green leafy vegetables, while vitamin K2 is found in fermented foods and animal products. A synthetic form of the vitamin, K3 (menadione), is not used in supplements due to its potential toxicity.


Vitamin K was first discovered in the 1920s by Danish scientist Henrik Dam, who noticed that chicks fed a cholesterol-free diet developed spontaneous bleeding and haemorrhages. Dam initially named the unidentified factor “Koagulationsvitamin” because of its role in blood coagulation, which is where the “K” in vitamin K comes from. Later, in the 1930s, American biochemist Edward Adelbert Doisy identified the chemical structure of vitamin K and was able to synthesise it. Both Dam and Doisy were awarded the Nobel Prize in Physiology or Medicine in 1943 for their ground-breaking work on vitamin K.

Since its discovery, researchers have continued to study vitamin K and have found that it is not only essential for blood clotting but also plays a vital role in bone health, heart health, and cellular growth and development.

In recent years, there has been growing interest in the different forms of vitamin K, particularly vitamin K2 and its various subtypes (MK-4 to MK-13). Studies have suggested that these different forms of vitamin K may have unique health benefits and that optimal intake of both vitamin K1 and K2 may be important for overall health. However, more research is needed to fully understand the specific roles and benefits of each form of vitamin K.

Functions of vitamin K

Vitamin K is an essential nutrient that plays a vital role in several important bodily functions. Some key functions of vitamin K include:

  • Blood clotting: Vitamin K is crucial for the synthesis of specific proteins that help in blood coagulation, such as prothrombin and other clotting factors. These proteins ensure proper blood clot formation to prevent excessive bleeding when an injury occurs.
  • Bone health: Vitamin K is involved in the regulation of calcium in bones. It activates proteins like osteocalcin, which helps bind calcium to the bone matrix, thereby supporting bone mineralisation and strength. Vitamin K has been associated with improved bone density and a reduced risk of fractures, particularly in older adults.
  • Heart health: Vitamin K may play a role in maintaining heart health by preventing the build-up of calcium in arterial walls, a process known as vascular calcification. Vitamin K activates a protein called matrix Gla protein (MGP), which inhibits calcium from accumulating in blood vessels, thereby reducing the risk of atherosclerosis and heart disease.
  • Cellular growth and development: Vitamin K is involved in the synthesis of certain proteins that regulate cell growth, division, and apoptosis (programmed cell death). It helps maintain proper cellular function and may play a role in preventing certain types of cancer, although more research is needed to confirm this association.
  • Anti-inflammatory properties: Some studies suggest that vitamin K may possess anti-inflammatory properties, which could help in reducing inflammation and managing inflammatory conditions such as arthritis. However, more research is needed to fully understand the extent of vitamin K’s potential anti-inflammatory effects.

Overall, vitamin K is essential for various critical functions within the body, underscoring the importance of consuming adequate amounts of this nutrient through a balanced diet.

Good Sources Of Vitamin K

Vitamin K is available in two primary forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). Vitamin K1 is found mainly in plant-based foods, while vitamin K2 is found in animal products and fermented foods. Here are some good sources of vitamin K1 and K2:

Vitamin K1 (phylloquinone) sources:

  • Green leafy vegetables: Kale, spinach, collard greens, Swiss chard, mustard greens, turnip greens, and beet greens are all excellent sources of vitamin K1.
  • Cruciferous vegetables: Broccoli, Brussels sprouts, and cabbage also contain significant amounts of vitamin K1.
  • Other vegetables: green beans, asparagus, and peas are additional sources of vitamin K1.
  • Herbs: Parsley, cilantro, and other fresh herbs contain vitamin K1.
  • Vegetable oils: Soybean oil, canola oil, and olive oil are good sources of vitamin K1.
  • Fruits: Kiwifruit and avocado contain moderate amounts of vitamin K1.

Vitamin K2 (menaquinones) sources:

  • Fermented foods: Natto (a Japanese fermented soybean dish) is a rich source of vitamin K2, particularly the MK-7 subtype.
  • Dairy products: Cheese (especially hard and aged varieties) and yogurt contain vitamin K2, specifically the MK-4 subtype.
  • Meat: Organ meats, such as liver and kidney, as well as dark meat poultry, are sources of vitamin K2.
  • Eggs: The yolks of eggs contain small amounts of vitamin K2.
  • Fish: Certain types of fish, such as salmon, mackerel, and herring, contain modest amounts of vitamin K2.

It is essential to consume a balanced diet that includes a variety of vitamin K-rich foods to ensure adequate intake of both vitamin K1 and K2. If you have concerns about your vitamin K intake or are on medications that interact with vitamin K, consult a healthcare professional for personalized advice.

How Much Vitamin K Do We Need?

According to the National Institutes of Health (NIH), the Adequate Intake (AI) levels for vitamin K vary depending on age, sex, and life stage. The AI levels are as follows:

  • Infants 0 to 6 months: 2.0 mcg/day (micrograms)
  • Infants 7 to 12 months: 2.5 mcg/day
  • Children 1 to 3 years: 30 mcg/day
  • Children 4 to 8 years: 55 mcg/day
  • Children to 13 years: 60 mcg/day
  • Teens 14 to 18 years: 75 mcg/day
  • Adults 19 years and older (males): 120 mcg/day
  • Adults 19 years and older (females): 90 mcg/day
  • Pregnant women 19+: 90 mcg/day
  • Breastfeeding women 19+: 90 mcg/day

These Adequate Intake levels are designed to ensure sufficient vitamin K levels for blood clotting and bone health in healthy individuals. It’s important to consume a balanced diet that includes vitamin K-rich foods to meet these recommendations. If you have concerns about your vitamin K intake or are on medications that interact with vitamin K, consult a healthcare professional for personalized advice.

Source: National Institutes of Health – Office of Dietary Supplements. (2021). Vitamin K – Fact Sheet for Health Professionals.

What Are The Signs of Vitamin K Deficiency?

Vitamin K deficiency is relatively rare in healthy adults since the vitamin is widely available in various foods and produced by gut bacteria. However, certain factors like poor diet, malabsorption disorders, and medications like long-term antibiotic use or blood thinners may increase the risk of deficiency.

Signs of vitamin K deficiency include:

  • Excessive bleeding: The primary function of vitamin K is to assist in blood clotting. A deficiency can lead to prolonged bleeding from minor cuts or injuries, as well as easy bruising and small blood spots under the skin (petechiae).
  • Heavy menstrual bleeding: Women with vitamin K deficiency may experience heavier-than-normal menstrual bleeding.
  • Bleeding gums: Vitamin K deficiency can cause bleeding gums when brushing or flossing teeth.
  • Nosebleeds: Frequent or unexplained nosebleeds can be another sign of vitamin K deficiency.
  • Blood in urine or stool: A deficiency in vitamin K may result in blood appearing in urine or stool.
  • Haematomas (blood suffusion): Large, deep bruises or haematomas may develop more easily in individuals with a vitamin K deficiency.
  • Reduced bone density: Vitamin K plays a role in maintaining bone health. A deficiency can lead to reduced bone mineral density and an increased risk of fractures.
  • In new-borns, vitamin K deficiency can lead to a rare but serious condition called vitamin K deficiency bleeding (VKDB), which may cause life-threatening bleeding in the brain or other organs.

If you suspect a vitamin K deficiency, consult a healthcare professional for proper diagnosis and treatment. In some cases, vitamin K supplements may be recommended to correct the deficiency, but it is essential to follow your healthcare provider’s guidance to avoid potential complications.

What Happens If I Take Too Much Vitamin K?

Vitamin K toxicity is rare since it is a fat-soluble vitamin and excess amounts are typically stored in the body without causing harm. However, extremely high doses of vitamin K can have some potential risks or side effects, especially if taken in supplement form.

  • Blood clotting issues: Excess vitamin K can potentially lead to excessive blood clotting, increasing the risk of thrombosis, which is the formation of blood clots within blood vessels. This can cause serious health problems, such as stroke or deep vein thrombosis (DVT).
  • Interference with anticoagulant medications: High doses of vitamin K can interfere with the effectiveness of blood-thinning medications, such as warfarin (Coumadin). For individuals taking these medications, it is crucial to maintain consistent vitamin K intake and avoid consuming large amounts of vitamin K without consulting a healthcare professional.
  • Allergic reactions: Although rare, some people may experience allergic reactions to vitamin K supplements, including symptoms like difficulty breathing, rash, or swelling.

In general, obtaining vitamin K from a balanced diet is considered safe, and toxicity is unlikely to occur from dietary sources alone. However, if you are considering taking vitamin K supplements, it is essential to consult a healthcare professional to determine the appropriate dosage and avoid potential risks or interactions with medications.