K2 is the form of vitamin K that your body uses to set up proteins involved in bone and heart health

Vitamin K2 is a type of vitamin K that works differently from K1 in your body. While K1 (found mainly in leafy greens) helps your blood clot, K2 activates proteins that direct calcium to your bones and teeth and away from your arteries. Your body can convert some K1 into K2, but not always efficiently, which is why K2 appears in food sources separately.

K2 comes from animal products and fermented foods — meat, dairy, eggs, and fermented vegetables like sauerkraut and natto (fermented soybeans). The amount varies widely depending on what the animal ate and how the food was prepared. This is why some people look for K2 specifically rather than relying on K1 conversion alone.

Key Takeaways

  • K2 activates proteins called osteocalcin and matrix Gla protein, which direct calcium to bones and teeth instead of soft tissues.
  • Food sources of K2 include grass-fed dairy, egg yolks, fermented foods, and certain cheeses, with amounts varying by production method.
  • Research suggests K2 may support bone density and cardiovascular health, though most studies are observational rather than controlled trials.
  • K2 deficiency is not formally recognized as a medical condition, but low intake may be common in Western diets that are low in fermented and animal foods.

How K2 works in bone health

K2 activates a protein called osteocalcin, which sits inside bone tissue and helps bind calcium to the bone matrix. Without K2, osteocalcin remains inactive and cannot do this job effectively. This is why researchers have looked at K2 intake in relation to bone density and fracture risk.

Several observational studies — where researchers follow people over time and track their diets and bone health — have found that people with higher K2 intake tend to have higher bone density. A study published in the American Journal of Clinical Nutrition found that women with the highest K2 intake had better bone density in the hip than those with the lowest intake. However, these studies cannot prove that K2 caused the difference; people who eat more K2-rich foods may also exercise more, eat more calcium, or have other habits that support bone health.

Controlled trials testing K2 supplementation on bone health are limited. Some small studies have shown modest improvements in bone density markers, while others have shown no effect. The research is still developing, and bone health depends on many factors beyond K2 alone — including calcium, vitamin D, exercise, and age.

K2 and cardiovascular health

K2 activates another protein called matrix Gla protein (MGP), which is found in blood vessel walls. When MGP is activated by K2, it may help prevent calcium from depositing in arteries — a process called arterial calcification. Over time, calcium buildup in arteries can stiffen them and contribute to heart disease.

Observational studies have found associations between higher K2 intake and lower risk of heart disease and arterial calcification. A large study in Europe followed thousands of people and found that those with the highest K2 intake had a lower risk of dying from heart disease over a 10-year period. Again, these are associations, not proof of cause and effect.

Controlled trials testing K2 supplementation for heart health are scarce. The research suggests a possible benefit, but it is not yet strong enough for doctors to recommend K2 supplements specifically for cardiovascular prevention. People interested in heart health benefit more from established practices like exercise, a diet rich in vegetables and whole grains, and managing blood pressure and cholesterol.

Food sources of K2

K2 is found mainly in animal products and fermented foods. The richest sources include grass-fed butter, hard cheeses (especially aged varieties like Gouda and Edam), egg yolks, and fermented soy products like natto. Fermented vegetables such as sauerkraut and kimchi also contain K2, though the amount depends on fermentation time and method.

The amount of K2 in food varies significantly. Grass-fed dairy products contain more K2 than grain-fed dairy because the cows eat more plants rich in K1, which they convert to K2. Natto is one of the most concentrated sources of K2 per serving, though it is not widely eaten outside Japan. Conventional cheese contains some K2, but aged cheeses have more because bacteria in the aging process produce additional K2.

If you eat a diet that includes dairy, eggs, and fermented foods, you are likely getting some K2. If you follow a vegan diet, you can get K2 from fermented soy products and fermented vegetables, though the amounts are typically lower than in animal sources.

K2 deficiency and daily intake

There is no official recommended daily amount for K2 in the United States. The recommended intake for total vitamin K (K1 and K2 combined) is 90 micrograms per day for adult women and 120 micrograms per day for adult men, but this guideline was based mainly on K1 research.

K2 deficiency is not formally recognized as a medical diagnosis. However, researchers have noted that Western diets tend to be low in K2 because they include less fermented food and less grass-fed dairy than traditional diets in other parts of the world. Whether this low intake causes health problems in most people is still an open question.

People at higher risk of low K2 intake include those who avoid dairy and eggs, those who do not eat fermented foods, and those taking certain medications (like some antibiotics) that may interfere with K2 production in the gut. If you fall into one of these groups and are concerned about K2 intake, talking with a doctor or registered dietitian can help you assess whether dietary changes or supplementation makes sense for your situation.

K2 supplements and safety

K2 supplements are available in two main forms: MK-4 (menaquinone-4) and MK-7 (menaquinone-7). MK-7 is derived from natto and has a longer half-life in the body, meaning it stays active longer. MK-4 is found in animal products and is absorbed quickly but does not stay in the bloodstream as long. Both forms are generally considered safe at typical supplement doses.

If you take blood-thinning medications like warfarin (Coumadin), you should not change your K2 intake — whether through food or supplements — without talking to your doctor first. Vitamin K can interfere with how these medications work. People on other medications should also check with their doctor or pharmacist before starting a K2 supplement, as interactions are possible.

K2 supplements are not regulated as strictly as medications, so quality and purity can vary between brands. If you are considering a supplement, look for third-party testing information on the label or the manufacturer's website.

What the research still does not know

Most K2 research to date has been observational — researchers track what people eat and their health outcomes over time, but cannot control all the other factors that affect health. To know whether K2 truly prevents bone loss or heart disease, researchers would need to run controlled trials where some people take K2 and others take a placebo, and both groups are followed for years. These trials are expensive and time-consuming, which is why they are limited.

Questions that remain unanswered include: How much K2 do you actually need? Does the form matter (MK-4 versus MK-7)? Does K2 supplementation prevent fractures or heart disease in people who do not have these conditions already? And does K2 work better when combined with adequate calcium and vitamin D? Research is ongoing, but definitive answers will take time.

Frequently Asked Questions

Can I get enough K2 from food without supplements?

If your diet includes dairy, eggs, and fermented foods, you are likely getting some K2. Whether that amount is optimal for bone and heart health is not yet clear. If you avoid these foods, a supplement may be worth discussing with your doctor, but food sources are generally preferred when possible.

Is K2 the same as K1?

No. K1 is found mainly in leafy greens and is used by your liver for blood clotting. K2 is found in animal and fermented foods and is used to set up proteins in bones and blood vessels. Your body can convert some K1 to K2, but not always efficiently.

Do I need a K2 supplement if I have weak bones?

Bone health depends on calcium, vitamin D, exercise, and other factors beyond K2. If you have weak bones or fracture risk, talk with your doctor about what testing and treatment make sense for you. K2 may be one piece of the picture, but it is not a substitute for established bone health strategies.

What if I am vegan and cannot eat K2-rich animal foods?

Fermented soy products like natto and fermented vegetables contain K2, though typically in lower amounts than animal sources. You can also discuss K2 supplementation with a registered dietitian who can help you assess whether it fits your needs and diet.

Will K2 supplements interact with my medications?

K2 can interfere with blood-thinning medications like warfarin. If you take any medications, ask your pharmacist or doctor before starting a K2 supplement, as other interactions are possible depending on what you take.