What is vitamin K2?
Vitamin K2 is a unique form of an essential micronutrient that plays an important role in heart health. Found in animal foods and fermented foods, vitamin K2 is often confused with vitamin K1 (which is found in plant foods) or overlooked altogether.
Let’s take a look at how much vitamin K2 you need, where you can get it, and potential benefits and side effects.
Vitamin K1 vs. K2: Food sources
Vitamin K is a fat-soluble nutrient that naturally exists in two forms: K1 and K2. Vitamin K1 is known as phylloquinone, while vitamin K2 is referred to as menaquinone.
The richest food sources of vitamin K1 include green leafy vegetables like kale, collards, spinach, Swiss chard, and turnip greens. Broccoli and Brussels sprouts are lesser known, but excellent sources of phylloquinone too. These diverse greens are nutrient-dense foods that most of us could use more of in our diets.
While vitamin K1 sources are plant-based, vitamin K2 foods come mostly from animals—namely egg yolk, dairy (e.g., butter and particular cheeses), chicken, eel, and organ meats. Vitamin K2 is also found in certain fermented foods, with sauerkraut, kefir, and nattō (fermented soybeans) being the most famous.
Vitamin K2 and your gut microbiome.
An additional and fascinating source of vitamin K2 comes from bacterial synthesis in our gut. The exact vitamin K2 contribution from our gut microbiota is challenging to quantify, and the amount produced varies from person to person. Nonetheless, having a healthy gut supports the synthesis of vitamin K2.
If you have taken antibiotics (and not replenished good gut bacteria through prebiotic and probiotic sources) or have suffered from gut infections or food sensitivities, you may not be producing as much vitamin K2.
Vitamin K2 and heart health benefits.
If you've ever heard of a coronary artery calcium (CAC) score1, this test checks for calcium buildup in the walls of your coronary arteries. A higher score means you have more plaque and are at a higher risk of a cardiovascular event from heart disease. While the process of atherosclerosis is complex—involving endothelial dysfunction, elevated ApoB-containing lipoproteins, oxidation, inflammation, and autoimmune dysregulation—one major feature of advanced plaque is vascular calcification.
Calcified plaques in your blood vessels can lead to serious (even fatal) blockages, which can manifest as angina, heart attack, and stroke. So, coronary calcification is something to be aware of and mitigate. Enter vitamin K2, your calcium “usher.”
- Supports normal calcium metabolism for improved bone health
- Deters dangerous calcium plaque buildup (arterial calcification) for heart health
How does vitamin K accomplish this? It activates important proteins like matrix GLA protein (MGP). In fact, MGP is dependent on vitamin K for its functions, and this protein keeps calcium from depositing into blood vessels and other soft tissues. Supporting this mechanism, several observational studies have linked higher vitamin K2 intake with lower coronary calcification.
- 52% reduced risk of severe coronary calcification
- 57% lower risk of coronary heart disease mortality
- 26% lower risk of all-cause mortality
Interestingly, no such heart health findings were observed for vitamin K1 intake.
The clinical trial evidence4 for vitamin K’s effect on cardiovascular disease is small but growing. While the results are mixed, that’s partially because the study designs are mixed too. Some clinical trials support vitamin K’s beneficial role in combating calcification and atherosclerosis; others do not. Future, well-designed clinical evidence will be valuable to further inform the vitamin K/heart health relationship.
Vitamin K: How much do I need?
- 90 micrograms per day for women
- 120 micrograms for men
Even though vitamin K is fat-soluble, it turns out that what we consume and synthesize is quickly utilized, metabolized, and excreted8 by our body. Add in the fact that very little vitamin K is stored, and it becomes clear why consuming the right foods is important to achieve daily vitamin K needs. Targeted supplementation can also be a useful strategy (we'll discuss that later).
Is vitamin K deficiency common?
While classic vitamin K deficiency is rare in the average adult, it can occur. The result is abnormal bleeding9 caused by impaired blood clotting. Possible symptoms to look out for and report to your doctor include bruising, nosebleeds, bleeding gums, bloody urine or stools, and very heavy menstrual bleeding.
People taking anticoagulant therapy (i.e., blood thinners) and those with liver disease or fat malabsorption disorders are at higher risk of experiencing vitamin K deficiency.
What about vitamin K insufficiency?
While not full-on deficiency, vitamin K insufficiency can occur when people fail to consume adequate vitamin K over time. Blood clotting may remain normal, since there’s enough vitamin K to conserve that vital function. But, more subtle and potentially serious consequences can occur.
Not getting enough vitamin K (and specifically K2) over time may contribute to chronic health conditions10 like osteoporosis (lower bone mineral density due to bone loss) and cardiovascular disease. Heart disease is the leading cause of death11 in the United States. And while the condition is known as the “silent killer,” vitamin K2’s important role in heart health should no longer remain silent.
Ideal vitamin K2 supplement dosage.
Whether in a multivitamin or standalone product, vitamin K2 supplements typically deliver menaquinones (MK) as MK-4 or MK-7 individually or in combination. Both are useful ways to augment the menaquinones that your diet and gut microbiome are providing. MK-7 may have better bioavailability12 than MK-4, but more studies should suss out this potential difference.
While there’s no scientific consensus on the amount of vitamin K2 you need, doses at or around 100 micrograms are found in supplements. And, a little vitamin K2 likely goes a long way. The Prospect-EPIC cohort study13 of over 16,000 Dutch women found that consuming 10 micrograms per day of additional vitamin K2 was associated with a 9% reduction in coronary heart disease risk. This is not a causal finding, but informative nonetheless.
Does vitamin K2 have side effects?
Vitamin K has an excellent safety profile, even at high doses. In fact, the National Academies Food and Nutrition Board did not even designate an upper limit for vitamin K1 or K2. That’s because no adverse effects14 have been documented from either form of vitamin K in humans or animal models when consumed via food or supplements.
Remember that your daily needs for vitamin K are 90 to 120 micrograms, depending on your gender. To put this recommendation in perspective, one-half cup of collard greens will deliver over 500 micrograms of vitamin K1, and three ounces of nattō pack a vitamin K2 punch at 850 micrograms. Supplements can deliver a range of vitamin K1 and K2 doses on top of what you consume from your diet.
Anticoagulants (such as Warfarin) have a known drug-nutrient interaction with vitamin K1. For this reason, some patients on anticoagulants think they should limit all sources of vitamin K. This is an unfortunate mistake that can create a vitamin K gap or deficiency. Direct oral anticoagulants (DOACs) do not have drug-nutrient interactions with vitamin K.
When taking blood-thinning medications, the important thing is to keep vitamin K inputs stable (not low). If a patient on blood thinners wants to incorporate vitamin K-dense foods (healthy foods!) into their diet or take a supplement containing vitamin K1 or K2, they should tell their doctor first. The healthcare practitioner will monitor key blood clotting biomarkers and adjust the medication accordingly.
Vitamin K is a common nutrient gap and essential fat-soluble vitamin that comes in two varieties: vitamin K1 and K2. While both forms of this micronutrient support normal blood clotting and improve bone health, it’s time to pay more attention to vitamin K2 when it comes to our heart health.
Remember, vitamin K2 is essentially the “usher” that directs calcium to all the right places (bones) while avoiding the wrong places like our arteries (heart). Supporting a healthy gut microbiome, consuming menaquinone-rich foods, and incorporating a vitamin K supplement (look for the K2 menaquinone form) are three practical ways to ensure you’re including this important form of vitamin K into your life.
Ashley Jordan Ferira, Ph.D., RDN is Vice President of Scientific Affairs at mindbodygreen. Ashley received her B.A. in Biological Basis of Behavior from the University of Pennsylvania (along with a double minor in Nutrition and Music) and Ph.D. in Foods and Nutrition from the University of Georgia. Her research contributions span vitamin D, cardiometabolic health, bone density, and weight management. Ferira is a nutrition scientist and dietitian with experience in nutrition product innovation and development, scientific affairs, education, communications, and SEO writing for global firms, including Nature Made, Metagenics, Three Ships, and mindbodygreen.
In addition to her mindbodygreen contributions, Ferira is published in Health, Metagenics Institute, American Family Physician, The Journal of Clinical Endocrinology & Metabolism, and Osteoporosis International. She has a passion for the translation of evidence-based science into innovative and high-quality products and information that help people lead healthier lives. She is a believer in compassionate, informed, and personalized approaches to nutrition, health care, and wellness. Ashley lives in beautiful Charleston, South Carolina, where she was born and raised. Whether savoring an orchestral performance or delectable meal at a local restaurant, you will find her enjoying Charleston’s cultural and culinary arts with family and friends.