What a Pharmacist Wants You To Know about Vitamin K2

Vitamin K2, or menaquinone (MK), is a type of vitamin K. Vitamin K is a collection of compounds the body needs to function. The K2 type may benefit bone, blood, and heart health. 

Vitamin K2 is found naturally in certain animal products and fermented foods, but most forms of vitamin K2 are naturally made by bacteria in the human gut. Supplements are also available to help increase your vitamin K2 levels. 

There are 10 types of vitamin K2, ranging from MK-4 through MK-13. Vitamin K2 subtypes MK-4, MK-7, and MK-9 are the most popular and well-studied.

Most people get plenty of vitamin K through their diet, but your healthcare provider may recommend you take a vitamin K2 supplement if you do not produce enough vitamin K2 or eat enough food containing the vitamin. 

Vitamin K2 has been shown to potentially support bone health. The vitamin helps create three substances crucial to bone health: carboxylase, osteocalcin, and matrix Gla protein (MGP). 

Carboxylase is an enzyme required to create proteins involved in bone growth and health. Osteocalcin and MGP bind with calcium to help build strong bones and reduce the risk of bone fractures.

Research has shown that vitamin K2 is specifically helpful in the overall bone health of people with osteoporosis. With long-term treatment (longer than two years), vitamin K2 may help reduce the number of bone fractures experienced while also helping to maintain the overall strength of bones (bone mineral density).

Vitamin K2 plays a role in the prevention of blood vessel hardening (calcification) by removing calcium from blood vessels. When calcium builds up in a blood vessel, the vessel hardens, making it more difficult for blood to flow through the body. 

Blood vessel calcification may lead to serious health conditions, such as high blood pressure (hypertension) and kidney disease, as well as death caused by coronary artery disease (CAD). And so, getting enough vitamin K2 might help prevent these conditions.

Vitamin K2 may support blood clotting abilities in the body. Again, vitamin K2 helps create the enzyme carboxylase. Carboxylase plays a major role in blood clotting. 

Normal blood clotting is important—if your blood doesn’t clot properly (or is too thin), you may be at risk for excessive bleeding or bruising. If your blood clots too easily (or is too thick), blood will not flow properly throughout your body. In turn, you could be at risk for serious health issues like stroke, heart attack, organ damage, or even death. 

Getting enough vitamin K2 means you can create the proper amount of carboxylase enzyme, giving your body what it needs to clot blood.

Vitamin K2 may play a role in the prevention of cancer. Some research has found that vitamin K2 may block the growth of cancer cells, specifically liver, lung, and pancreatic cancer cells. Meanwhile, other research shows that vitamin K2 may reduce the risk of death caused by cancer but not the actual diagnosis of cancer. 

Overall, more studies are needed to confirm if—and in what way— vitamin K2 may protect against cancer. 

Vitamin K2 can be found in various animal-based and fermented foods. 

Examples of animal products that contain vitamin K2 include:

Chicken (chicken breast, chicken liver)
Beef (ground beef, beef liver)
Ham
Salmon
Shrimp
Eel
Hard cheeses (gouda, cheddar) 
Soft cheeses (blue cheese)
Eggs (egg yolks, hard-boiled eggs)

Fermented foods are foods made with microorganisms like bacteria and yeast. The microorganisms, which can exist in the food naturally or be added, break down ingredients like sugars and convert them into other products, like gasses. Fermented foods that contain vitamin K2 include natto (a Japanese food made from fermented soybeans) and sauerkraut.

Mixed nuts can also be a good source of vitamin K2.

Vitamin K (including vitamin K2) deficiency is rare in the United States as most people receive enough vitamin K through their diet. However, some populations, including people unable to properly absorb the vitamin in their gastrointestinal (GI) tract, may require supplementation.

Vitamin K2 may be included in a multivitamin or combination product (often with calcium, magnesium, vitamin D, or other vitamin K subtypes). The amount of vitamin K2 in a supplement is dependent on the product. However, most products usually have less than 75% of the recommended daily value. 

Vitamin K2 supplements may also be available as a single product, usually with only one vitamin K2 subtype (such as MK-4 or MK-7).

Dosage

Your dosage of vitamin K2 depends on factors like your age, sex, and diet, as well as health conditions you may have. 

The National Institutes of Health (NIH) and the Food and Nutrition Board have set daily recommended amounts of vitamin K. These recommendations are based on all types of vitamin K, not specifically vitamin K2. 

The recommended daily intake for vitamin K is 120 micrograms (mcg) for adult men and 90 mcg for adult women, including people who are pregnant or lactating.

The amount of vitamin K2 in a supplement depends on the product. Most vitamin K2 products are available as a capsule or softgel, taken by mouth. The recommended dosage may depend on the product used.

For example, vitamin K2 subtype MK-7 is available as a supplement. The recommended dosing is usually between 50-120 mcg a day but can range from 5-600 mcg. MK-7 doses between 180-360 mcg a day have shown heart-health benefits.

Talk with your healthcare provider or pharmacist about which type of vitamin K2 supplement and dosage may be best for you.

Vitamin K2 is considered safe. There has been no reported toxicity in studies with vitamin K2. Doses of vitamin K2 up to 45 milligrams (45,000 mcg) have safely been used in studies for up to two years.

Potential Drug Interactions

Vitamin K2 may interact with medications you are already taking. Examples of medications that can interact with vitamin K2 include:

Warfarin: This blood thinner (brand names include Jantoven and Coumadin) cancels out the activity of all vitamin K types, including vitamin K2—specifically blood-clotting abilities. Any sudden changes in vitamin K intake can increase or decrease the blood clotting effects of warfarin. This means your blood may become thicker or thinner, which may cause serious health issues.
Antibiotics: These medications can change gut bacteria that create vitamin K2, potentially lowering the level of vitamin K2 in your body. This interaction is most noticeable with a group of antibiotics called cephalosporins, which include Keflex (cephalexin) and Omnicef (cefdinir). If you take antibiotics longer than 10 days and have a low vitamin K2 intake, your healthcare provider may recommend a vitamin K2 supplement.
Bile acid sequestrants: Bile acid sequestrants are a class of medications used to lower cholesterol levels. Examples of bile acid sequestrant drugs include Prevalite (cholestyramine), Colestid (colestipol), and Welchol (colesevelam). These medications may lower the absorption of vitamin K2 in your body.
Orlistat: Available over-the-counter (Alli) or as a prescription (Xenical), Orlistat is a drug used for weight loss. Orlistat can lower the absorption of vitamin K2 in your body.

What To Look For

Unlike prescription and over-the-counter (OTC) medications, supplements like vitamin K2 are not regulated by the U.S. Food and Drug Administration (FDA). Therefore, shopping for vitamin K2 products tested by independent third-party organizations helps ensure the ingredients listed are actually the ingredients in the supplement. 

Popular organizations that offer quality testing include United States Pharmacopeia (USP), NSF International, and ConsumerLab.com. You can look for their labels on the product packaging.

Can You Take Too Much Vitamin K2?

Vitamin K2 has not been shown to cause harm or toxicity. Therefore, the NIH and Food and Nutrition Board have not established a maximum upper level or dose of vitamin K2. Taking high doses of vitamin K2 is unlikely to cause adverse health effects.

Vitamin K2 has minimal side effects. The most common side effects reported are gastrointestinal issues like diarrhea, nausea, or upset stomach.

Skin rash has also been reported with vitamin K2 and should improve after stopping the supplement.

Vitamin K2, or menaquinone, is a type of vitamin K made in your gut and available in certain foods. Vitamin K2 is useful in bone health, as well as for overall blood and heart health. If your body doesn’t produce enough vitamin K2 or you can’t gain enough of the vitamin from your diet, your healthcare provider may recommend you take a vitamin K2 supplement.

If you are interested in taking a vitamin K2 supplement, talk with your healthcare provider about whether the supplement would benefit you. They can discuss dosage, safety concerns, and side effects.