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Vitamin K

Phylloquinone (K1); Menaquinone (K2); Menadione (K3)

Overview

Vitamin K is fat-soluble Vitamin that plays a role in blood clotting in the body. It comes in two forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones).

Vitamin K1 is naturally found in some foods, such as green vegetables like collard greens, spinach, and broccoli. Vitamin K2, one of the main forms of Vitamin K, is synthesized by the bacteria found in the intestines.

Vitamin K is also available as a dietary supplement. However, most people get the amount of Vitamin K they need through diet alone. It is injected as a supplement in newborns, though, as they do not produce Vitamin K right away nor do they get sufficient amounts from breast milk.

In the United States, the Food and Drug Administration (FDA) does not regulate supplements the way it regulates prescription drugs. That means some supplement products may not contain what the label says. When choosing a supplement, look for independently tested products and consult a healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist.

What is Vitamin K?

Vitamin K is a fat-soluble Vitamin (meaning it dissolves in fat). It helps your body develop and function properly. There are two types of Vitamin K, which come from different sources:

Vitamin K1, or phylloquinone (pronounced “fil-oh-kwi-nohn”): This more common type is found mostly in plant foods, especially green leafy vegetables like spinach and kale.

Vitamin K2, or menaquinone (pronounced “men-ah-kwi-nohn”): This less common type is found in some animal foods and fermented products. Gut bacteria in your body also produce this type.

Uses of Vitamin K

There is little research to suggest that Vitamin K can play a role in disease prevention. The main use of Vitamin K is to treat a Vitamin K deficiency, which is rare in the United States.

Vitamin K is routinely provided as an intramuscular (IM) injection to newborns to prevent deficiency. The American Academy of Pediatrics recommends that Vitamin K be given within the first six hours of life to all newborns.

No supplement is intended to treat, cure, or prevent disease. However, Vitamin K has also been researched for its role in:

Blood clotting

Bone health

Heart disease prevention

Blood Clotting

Vitamin K helps produce the proteins in the body that are essential for blood clotting. Vitamin K therapy has been used to reverse the effects of anticoagulants (blood thinners).

An example of this may be someone prescribed anticoagulants who suddenly requires emergency surgery. In this case, 2.5 to 5 milligrams (mg) of Vitamin K can be administered to reverse the anticoagulation effects and prevent excess bleeding.

Bone Health

Vitamin K is thought to contribute to bone health due to its role in producing proteins responsible for bone formation. However, there is not enough research on Vitamin K to show whether Vitamin K supplementation plays a direct role in improving bone health or preventing osteoporosis.

Results of research on Vitamin K for osteoporosis prevention are mixed and include:

Research suggests that Vitamin K and calcium combined may improve bone mineral density.

One 2017 study showed that higher levels of Vitamin K intake may be associated with modest reductions in bone fractures (breaks).

Other studies have found no evidence that Vitamin K improves bone mineral density or reduces vertebral fractures. An additional study found that Vitamin K had no effect on bone mineral density, and the authors concluded that the results did not support a role for Vitamin K in osteoporosis prevention.

Heart Disease Prevention

Research on Vitamin K supplementation for heart disease prevention has been inconclusive.

Vitamin K has a role in the formation of a protein called matrix Gla-protein (MGP). MGP blocks vascular calcification (mineral deposits in the walls of the arteries and veins), but it depends on Vitamin K for activation. Vascular calcification is associated with an increased risk of heart disease.

However, it is still unclear whether supplementing Vitamin K can slow vascular calcification.

Furthermore, a review in the Cochrane Database concluded that there is not enough evidence to support the use of Vitamin K in the primary prevention of heart disease.

Vitamin K Deficiency

Vitamin K deficiency is rare in adults but happens often in infants.

Newborns are routinely given a standard Vitamin K injection right after birth to prevent deficiency.

This is because:

Newborns do not produce Vitamin K right away.

Vitamin K from the mother doesn't transfer well to the baby.

Breast milk has a low Vitamin K content.

In adults, Vitamin K deficiency is most often related to malabsorption disorders. People with malabsorption disorders like cystic fibrosis (CF), celiac disease, Crohn's disease, and short bowel syndrome may need supplemental Vitamin K.

What Causes a Vitamin K Deficiency?

A Vitamin K deficiency can occur from inadequate intake or poor absorption in the gastrointestinal (GI) tract.

Most people get enough Vitamin K in their diets. The bacteria in our GI tract also synthesize (combine with) Vitamin K.

Poor absorption of Vitamin K occurs secondary to a GI condition or malabsorption (difficulty in absorbing or digesting nutrients). Poor absorption may also be a side effect of some medications.

Groups at Risk of a Vitamin K Deficiency

Those at greatest risk of a Vitamin K deficiency include:

Newborns if they do not receive a standard Vitamin K dose after birth and are exclusively breastfed

People with GI diseases that result in reduced absorption or fat malabsorption (e.g., celiac disease, Crohn's disease, bowel resections)

People with pancreatic insufficiency (when the pancreas does not make enough enzymes to absorb nutrients), such as those with CF

People with alcohol use disorder or severe malnutrition

People with a deficiency as a result of fat malabsorption should take an oral supplement of Vitamin K in a water-soluble form.

Although rare, there are a few case reports of Vitamin K deficiency and complications in people and their infants after experiencing hyperemesis (severe nausea and vomiting) during pregnancy.

How Do I Know If I Have a Vitamin K Deficiency?

Vitamin K status can be evaluated by assessing dietary intake and absorption.

If you have a GI condition or fat malabsorption, you are at greater risk of Vitamin K deficiency. Symptoms of malabsorption include frequent diarrhea, light-colored stools, and weight loss.

Vitamin K levels in the blood are not routinely assessed in most people, nor are they a good way to measure for Vitamin K.

Prothrombin time is an indicator of Vitamin K status. Prothrombin time is a measure of the time it takes blood to clot. In those prescribed anticoagulants, prothrombin times are routinely assessed to monitor the effectiveness of anticoagulant dosing.

Someone with a Vitamin K deficiency will also bruise or bleed more easily. Although uncommon, ecchymosis or petechiae (skin conditions) may also be present.

What Are the Side Effects of Vitamin K?

Vitamin K supplements aren't recommended unless your healthcare provider indicates you need additional Vitamin K. Side effects of supplementing Vitamin K are rare when taken at the recommended dose.

There may be side effects of taking Vitamin K and medications such as blood thinners, aspirin, antibiotics, and more. Taking Vitamin K with blood thinners can make the medication less effective. Antibiotic use may block the action of and reduce Vitamin K status in the body

When applied to the skin: Vitamin K1 is possibly safe for most people when applied as a cream that contains 0.1% Vitamin K1.

Precautions

Since Vitamin K works to clot the blood, those prescribed the blood-thinning medication Jantoven (warfarin) or those with clotting disorders must be mindful of their Vitamin K intake.

Adding more Vitamin K to your usual intake will make the medications less effective. It is important to keep your Vitamin K intake consistent.

When applied to the skin: Vitamin K1 is possibly safe for most people when applied as a cream that contains 0.1% Vitamin K1.

Pregnancy and breast-feeding: Vitamin K is likely safe when taken in recommended amounts of 90 mcg daily for those over 19 years old. Don't use higher amounts without the advice of a healthcare professional.

Children: Vitamin K1 is likely safe when taken by mouth appropriately.

Kidney disease: Too much Vitamin K can be harmful if you are receiving dialysis treatments due to kidney disease.

Dosage: How Much Vitamin K Should I Take?

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your needs.

Most people can meet their Vitamin K needs through diet alone. For supplementation, dosing can vary depending on the cause of the deficiency.

At birth, newborns routinely receive a 0.5 to 1 mg Vitamin K intramuscular injection to prevent a deficiency.

Adequate Intakes for Vitamin K
Age and Sex	Daily AI (in micrograms) (µg)
Infants 0–6 months	2
Infants 7–12 months	2.5
Children 1–3 years	30
Children 4–8 years	55
Children 9–13 years	60
Teens 14–18 years	75
Adults 19 years or older	90
Pregnant/nursing females younger than age 19	75
Pregnant/nursing females older than age 19	90
Males 19 and older	120

Note that the AI for Vitamin K is provided in micrograms (mcg). Some dosing suggestions for Vitamin K are in milligrams.

For conversion, 1 mg equals 1,000 mcg. When looking at supplements, it is important to look at the amounts and units of measure

What Happens If I Take Too Much Vitamin K?

There are no known adverse events associated with excess Vitamin K intake. There is also no tolerable upper limit (TUL) set for Vitamin K.

Those who require anticoagulant medications should be mindful of their Vitamin K intake since it can reduce the effectiveness of their medication.

Interactions

Vitamin K interacts with the following medications:

Warfarin and other anticoagulants: These drugs work to deplete Vitamin-K-dependent clotting factors. Sudden changes in Vitamin K intake could alter the anticoagulant effect of the medication. People prescribed warfarin or other anticoagulants are instructed to keep their Vitamin K intake consistent.

Antibiotics: Antibiotics may kill bacteria in the gut that usually produce Vitamin K. Supplements may only be necessary if antibiotics are required over several weeks or they are accompanied by a poor Vitamin K intake.

Bile acid sequestrants: Bile acid sequestrants include cholestyramine and colestipol. They prevent the reabsorption of bile acids, ultimately reducing cholesterol levels. They may also reduce Vitamin K levels, particularly if taken for several years.

Orlistat: Orlistat is a medication available both as an over-the-counter (OTC) and prescription product for weight loss. It works by reducing fat absorption, which could, in turn, reduce fat-soluble Vitamin absorption. A multivitamin with Vitamin K may be suggested in conjunction with orlistat.

Sources of Vitamin K & What to Look For

Vitamin K is mostly obtained through diet.

It is also available as a single nutrient supplement and in multivitamin products. The amount of Vitamin K in multivitamin products is usually less than 75% of the daily value.

Vitamin K can be found in fat-soluble Vitamin products, which may also contain Vitamins A, D, E, and K.

Food Sources of Vitamin K

Dietary sources of vitamin K-1 include:

dark leafy green vegetables, such as spinach, kale, and collards

lettuce

turnips

broccoli

carrots

vegetable oils

blueberries

grapes

Dietary sources of vitamin K-2 include:

natto, a traditional Japanese dish of fermented soybeans

sauerkraut

dairy products, especially hard cheeses

liver and other organ meats

beef

pork

egg yolks

chicken

fatty fish, such as salmon

One Final Note..

Vitamin K is a fat-soluble Vitamin that doesn't require supplementation very often. It is easy to get adequate amounts of Vitamin K through the diet, and a deficiency is rare. Certain fat malabsorption disorders may put you at higher risk of a deficiency.

Vitamin K functions to help with blood clotting. Therefore, sudden changes in the amount of Vitamin K consumed can make anticoagulant medications (e.g., warfarin) less effective.

If you suspect you need to supplement Vitamin K, it should be discussed with your healthcare provider first

Vitamin K is fat-soluble Vitamin that plays a role in blood clotting in the body. It comes in two forms: Vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones).

Vitamin K1 is naturally found in some foods, such as green vegetables like collard greens, spinach, and broccoli. Vitamin K2, one of the main forms of Vitamin K, is synthesized by the bacteria found in the intestines.

Vitamin K is also available as a dietary supplement. However, most people get the amount of Vitamin K they need through diet alone. It is injected as a supplement in newborns, though, as they do not produce Vitamin K right away nor do they get sufficient amounts from breast milk.

In the United States, the Food and Drug Administration (FDA) does not regulate supplements the way it regulates prescription drugs. That means some supplement products may not contain what the label says. When choosing a supplement, look for independently tested products and consult a healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist

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Most recent revision October 14, 2025 10:09:16 AM

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