Vitamin K (Class)

Vitamin K is an essential nutrient that helps the blood clot with vitamin K1 and vitamin K2 as the most important compounds of this vitamin group.


Vitamin K is a fat-soluble vitamin stored in very small amounts in the body which may often become depleted during dietary intake. Because the body is unable to store vitamin K, it recycles itself several times for protein carboxylation, therefore decreasing the need as a daily requirement. The naturally occurring forms of vitamin K are phylloquinone (vitamin K1), menaquinones (vitamin K2), menaphthone or menadione (vitamin K3). The main form of vitamin K available in North America is vitamin K1 as it is stronger, less toxic, works quickly and is beneficial for certain medical conditions. Vitamin K derives from the German word “Koagulationsvitamin.”

Food sources of vitamin K1, green leafy vegetables, preferably used raw, include kale, Swiss chard, green leaf lettuce; spinach, watercress, parsley, and broccoli while some plant-based oils such as soybean, olive, canola and cottonseed are major contributors of dietary vitamin K too. If anticoagulant medications are being taken, avoid consuming large amounts of these foods. High doses of vitamin K may disrupt the medications efficiency.

Menaquinones or vitamin K2, commonly found in fermented foods such as cheese, curds, and Natto, a traditional Japanese food made from fermented soybeans, differ in degree within levels of vitamin K. This determination source is on bacterial strains and fermentation process. To estimate the contribution of menaquinones to vitamin K is difficult due to limited research and variations in populations along with food consumption practices. A bacterium that forms in the large intestine can absorb menaquinones where the bile salts are lacking; however, all forms of vitamin K become absorbed in the small intestine.

Ordinarily not considered a natural vitamin K, vitamin K3 is indispensable for the production of prothrombin (factor II) and other clotting factors in humans: VII, VIII, IX, and X. All of the clotting factors, with the exception of VIII, are created in the liver, while factor VIII production starts in the endothelial cells of the blood vessels.

Vitamin K helps the blood clot in order to prevent excessive bleeding and reverse the effects of blood thinners. Low levels of vitamin K can add to the risk of uncontrolled bleeding. Although vitamin K deficiencies are uncommon in adults, they can be common in newborns and an injection of vitamin K is standard for infants. Prevention and treatment of osteoporosis and bone losses caused by steroids, the possibility of lowering cholesterol in people on dialysis are examples of potential improvement by use of vitamin K.

A man-made form of vitamin K, Mephyton, used to treat vitamin K deficiency or bleeding problems caused by various disorders, is available in tablet, capsule or injection form. Insufficient vitamin K can lead to poor blood clotting, increased bleeding and osteopenia. Symptoms include bruising easily, gastrointestinal bleeding, heavy menstrual bleeding and blood in the urine. At risk are those people with chronic malnutrition, alcohol dependency and anyone with health conditions such as Crohn's or celiac disease, that limit the incorporation of dietary vitamins due to the disease affecting digestive tract absorption.

Conditions treated:

  • Osteoporosis
  • Unusual bleeding
  • Decreased blood clotting
  • Reversing effects of warfarin
  • Prevent bleeding problems in newborns
  • Cancer
  • Heart disease

Type of Medicine:

  • Brand name: Mephyton (phytonadione)
  • Generic name: Vitamin K - Oral

Side Effects:

The two forms of vitamin K, K1 and K2 are more than likely safe for the majority of people when taken properly as directed. Oral vitamin K overdoses are rare. Even if there are no adverse effects of vitamin K supplements or foods containing vitamin K, this does not mean that a high dosage can't be dangerous in any way. Side effects may occur as a result of your body adjusting to the new medication. Always ask your health care provider about the possibility of any side effects and the best way to address these issues should they take place.

Less common side effects:

  • Paleness
  • Decreased appetite
  • Enlarged liver
  • Irritability
  • Muscle stiffness
  • Decreased movement or activity


  • Low blood pressure
  • Fast and/or weak heartbeat
  • Increased sweating
  • Tightness in chest
  • Fainting
  • Shortness of breath

However, if an allergic reaction, including rash, itching, swelling – especially of the face, tongue, or throat – dizziness, trouble breathing occurs, call your doctor or reach out to the FDA at 1-800-FDA-1088 or the Poison Help line on 1-800-222-1222, if there is suspicion of overdose.


The amount of medicine taken depends on your age, the strength of the medication, the number of doses taken each day along with medical condition and response to treatment. The usual dose for adults and children is 5 to 10 milligrams (mg) a day with problems occurring from blood clots, increased bleeding or for vitamin supplementation. The dosage for problems with blood clotting or increased bleeding only for adults and teenagers is 2.5 to 25 mg, repeated as necessary. Vitamin K is not recommended for use by young children as there may be sensitivity to the effects of vitamin K with high doses of menadiol or phytonadione.

There is no specific information regarding the use of vitamin K in the elderly, thus, it is unknown if side effects or problems would occur at the same rate as with younger individuals.

The Recommended Dietary Allowance (RDA) has not set limitations in favor of vitamin K supplements since there are insufficient details to create an average. Establishment of intake based on analysis and experimental data determines the outcome.

Adequate intake of vitamin K from both food and other sources:

  • 2 micrograms/day up to 75 micrograms/day for children and teens
  • 90 micrograms/day up to 120 micrograms/day for women and men 19 years old and older
  • 75 micrograms/ day up to 90 micrograms/day for pregnant or breastfeeding women; the former under the age of 19 years old and the latter over 19 years old

If a healthcare provider has prescribed this product, take this medication by mouth exactly as directed. Vitamin K can decrease the effects of warfarin for up to two weeks; therefore, taking both vitamin K and warfarin precisely as intended is of the utmost importance. Bleeding or bruising occurrences need immediate medical attention as you may require another dose of vitamin K.

Do not increase your dosage or use the drug longer than needed as it will not improve your condition quickly and the risks of side effects may become greater. If you miss a dose, contact your provider for instructions going forward.

Prescription and over-the-counter vitamin K differ by dosage and strength. A common form of over-the-counter vitamin K is water soluble chlorophyll, which is available in tablet, capsule or liquid forms.

Major Drug Interactions:

Certain medications should not be used together due to possible allergic reactions or the potential of each drug to negatively interact creating potency loss. People taking medications on a regular basis should have a thorough discussion with their doctor about including vitamin K as a part of their regimen. Below is a partial list of drugs that may interact poorly with vitamin K:

  • Blood thinners / Coumadin
  • Antibiotics
  • Aspirin
  • Drugs for cancer and seizures
  • High cholesterol
  • NSAIDs
  • Orlistat (a weight-management drug)
  • Bile acid sequestrants

Caution should be taken when using the following herbs and supplements:

  • Vitamin A
  • Vitamin E
  • Tiratricol
  • Devil's claw
  • Fenugreek
  • Guar gum
  • Panax ginseng
  • Siberian ginseng
  • Coenzyme Q-10


High doses of Vitamin K may cause numbness or tingling in the extremities, although no other known toxicity is associated with continued use. Vitamin K supplements should not be taken without a health care provider's recommendation. A medicine used for heart problems or clotting disorders, such as Coumadin, may require the patient to watch their diet closely in order to control the amount of vitamin K intake.

Additional vitamin K supplementation taken during pregnancy may increase the risk of jaundice in newborns. Vitamin K1 is considered compatible with breastfeeding, according to The American Academy of Pediatrics, but caution is recommended.

Vitamin K1 may decrease blood sugar levels in diabetics, but blood sugar needs to be monitored closely as the diabetic medication might need to be changed as a result of blood sugar being too low. Eating food or certain types of food, along with alcohol or tobacco, may cause interactions to occur. Discussions with your health care provider can eliminate which foods or drink can do the most harm.

Other medical problems affecting the use of vitamin K:

  • Gallbladder disease
  • Intestinal problems
  • Liver disease
  • Cystic fibrosis
  • Pancreatic cancer
  • Kidney disease


Medicine and vitamins can be expensive, so it's important to make sure that your products are stored properly. Keep vitamin K in the original container at room temperature between 59-86 degrees F and away from moisture, cold, heat or direct light. Placing your supplements in the refrigerator can be an option as well, but be sure to read the label. Avoid placing vitamin K in the bathroom cabinet, as the humidity can lessen the effectiveness over time.

Do not flush medication down the toilet or pour them down the drain unless this is a recommendation. Make sure you put all items well out of the reach of children and pets. Check with your healthcare provider or local community concerning disposal of outdated medication.


When added to a balanced diet, vitamins are needed in small amounts for growth and health. Vitamin K is crucial for normal clotting of the blood in addition to assisting the transport of calcium throughout the body. Without enough vitamin K, the potential for blood loss, as well as the inability for natural blood clotting, may result.

Vitamin K2 may also be helpful for bone health, reducing bone loss and bone fractures, although research in this area is conflicting. Not enough data has been established to support vitamin K2 as a treatment for osteoporosis or cardiovascular disease. There is also insufficient evidence to rate vitamin K's effectiveness for breast cancer, diabetes, high cholesterol, cystic fibrosis, prostate cancer or stroke.

Applying vitamin K to remove spider veins, bruising, scars, stretch marks, and burns or to treat rosacea topically are an additional probability open to discussion, since there is not enough evidence to support claims of actual results.

It is important that prescribed vitamin K be taken as directed by your health provider, but before you take Mephyton (phytonadione), tell your doctor about all medical conditions or allergies in order to determine if this is the correct course of action for treatment. Informing all your health care providers about the use of vitamin K is imperative.

Your diet should include a variety of vegetables, fruits, whole grains and proteins, with limits on saturated and trans fats, added sugars and sodium. If you are taking more than one medication, you need to know what risks are involved as a number of drugs can interfere with vitamin K. One of the most important things to remember about vitamin K intake is being consistent with your medication and having constant communication with your healthcare provider about any changes that occur.

Last Reviewed:
December 23, 2017
Last Updated:
April 05, 2018
Content Source: