How much do you know about vitamin K? Perhaps very little.
Vitamin K is involved in important bodily processes, such as blood clotting and building strong bones. Now, some studies suggest vitamin K may slow the rate of calcium buildup in the coronary arteries, prompting some people to wonder if they should take vitamin K supplements to help prevent a heart attack.
“The data are encouraging, but we are still far from vitamin K being an established therapy for coronary artery disease (CAD),” says Cleveland Clinic preventive cardiologist Abhayjit Singh, MD.
What Is Vitamin K?
Vitamin K is a fat-soluble vitamin that has an essential role in several human physiologic functions.
Vitamin K comes in two primary forms: Vitamin K1 (phylloquinone) and vitamin K2 (multiple menaquinones designated MK-4 through MK-13, with the most studied forms being MK-4, MK-7 and MK-9). We get both types of vitamin K through our diet, and both are available as supplements and in multivitamins.
What Vitamin K1 and Vitamin K2 Do in the Body
Most people know vitamin K through the anticoagulant (“blood thinner”) warfarin (Coumadin), which is widely used to prevent heart attack- and stroke-causing blood clots in people with cardiovascular disease and mechanical valves.
Vitamin K1 activates proteins made in the liver known as clotting factors. When activated, these proteins bind with calcium, attach themselves to blood vessels and turn blood into clots formed from fibrin and platelets. Warfarin prevents vitamin K from activating the clotting factor prothrombin. “Without vitamin K, blood cannot clot,” Dr. Singh says.
Vitamin K2 plays a key role in bone metabolism. Bones continually break down and rebuild. Vitamin D helps the body absorb calcium from food. Vitamin K2 activates a protein called osteocalcin, which directs calcium to the bones and orders the bones to retain it, building bone and keeping it strong.
Vitamin K2 also activates matrix GLA-protein (MGP), which is found in vascular smooth muscle cells, bones and cartilage. Activated MGP prevents calcium from being deposited in the blood vessels, ensuring it is available for bone health. It is vitamin K’s interaction with MGP that is being investigated for its potential in heart health.
Potential Health Benefits of Vitamin K
Researchers are examining multiple potential beneficial effects of vitamin K in the body.
Osteoporosis Prevention
Vitamin K promotes bone strength by helping the bones retain calcium, which may prevent the consequences of calcium-depleted bones, including hip fractures and osteoporosis. To date, however, studies on the effect of vitamin K2 supplements on bone density have produced conflicting results. Outcomes have varied depending on the dose of vitamin K used, whether the vitamin was given alone or with other treatments, whether or not the study participants had osteoporosis, and their vitamin K status at the conclusion of the study.
“Although vitamin K shifts bone-related biomarkers in a positive way that trends toward better bone health, we still lack hard data that it increases bone density or prevents fractures,” Dr. Singh says. “That’s why it isn’t standard of care for treating osteoporosis.”
Heart and Blood Vessel Health
MGP, the vitamin K-dependent protein that prevents calcium from being deposited in blood vessels, may have a role in heart disease prevention.
“We think the same process that contributes to calcification in bones is involved in the process in which arterial walls and beds undergo calcification, which subsequently manifests as coronary artery disease or peripheral artery disease,” Dr. Singh says.
Vitamin K’s effects on the arteries have become a hot topic in heart health, but few studies examining the effect of vitamin K on arterial calcification have been performed. That’s why a clinical trial published June 10, 2026, in JAMA Cardiology has attracted so much interest.
In this randomized, placebo-controlled trial, people with symptomatic CAD were given vitamin K2 (MK-7) supplements or a placebo for two years. The primary outcome was change in coronary artery calcium score, as measured by computed tomography (CT) and CT angiography. At the end of the study, the progression of coronary artery calcium was 29% less in those taking vitamin K than in those taking placebo.
“This was a well-run trial and by far the most encouraging results we have had. However, there were no hard outcomes. It only concluded that if you take this vitamin, the calcium load in your coronary arteries will progress less,” Dr. Singh says. “What was the clinical significance of this finding? Was the participants’ risk of heart attack or stroke lower? It just didn’t provide the kind of definitive evidence we are looking for to say vitamin K is going to be in the armamentarium of treatments we use to manage coronary artery calcification.”
There is another hurdle, as well. Coronary artery calcium scoring is used in risk stratification because higher degrees of coronary artery calcium trend toward an increased risk of coronary events. However, using coronary artery calcium progression to gauge the effectiveness of vitamin K as a therapy for coronary artery disease is debatable.
“If I have coronary artery calcification and do nothing about it, and my calcium burden progresses, my cardiovascular risk will go up. If I have coronary artery calcification and take a statin, my calcium burden will progress, but my cardiovascular risk will go down,” Dr. Singh explains. “It’s not as simple as, ‘Coronary artery calcium is bad, and more coronary artery calcium is worse.’”
Best Food Sources of Vitamin K
Vitamin K1 is found primarily in leafy, dark green vegetables. The best sources are:
- boiled collard greens
- boiled turnip greens
- raw spinach
- raw kale
- cooked broccoli
Vitamin K1 is also found in other vegetables, fruits and nuts, including:
- canned pumpkin
- carrot juice
- pomegranate juice
- grapes
- blueberries
Soybean, canola, and olive oils are good sources of vitamin K1. Moreover, small amounts of vitamin K1 are found in chicken breast, ham, ground beef, eggs, and butter from grass-fed cows
Vitamin K2 is obtained from fermented foods, such as:
- natto (fermented soy)
- sauerkraut
- kefir
- some cheeses (raclette, Vacherin Fribourgeois, Jarlsberg, Emmentaler, aged Gouda)
Note: The vitamin K2 content of these foods depends on the bacterial culture used in the fermentation process.
The amount of vitamin K you absorb from food is generally less than the amount of vitamin K the food contains, due to variations in bioavailability. Vitamin K1 in oils and dietary supplements is more bioavailable than the vitamin K1 in green vegetables and other plants. Because vitamin K is a fat-soluble vitamin, consuming vitamin K-containing foods along with fat enhances absorption of the vitamin.
Signs of Vitamin K Deficiency
Severe vitamin K deficiency, although rare, can cause:
- bruising
- bleeding
- hemorrhage
Who May Be at Risk for Low Vitamin K?
Certain populations may be at increased risk of vitamin K deficiency or insufficiency.
Newborns
Infants are naturally deficient in vitamin K due to low levels of clotting factor, poor transfer of vitamin K1 from the mother through the placenta, and the low vitamin K content of breast milk. As such, infants can develop a condition known as vitamin K deficiency bleeding (VKDB), in which bleeding occurs in the umbilical cord, gastrointestinal tract, skin, nose or other body site. VKDB can occur in infants fed exclusively with breast milk and those with malabsorption issues. VKDB occurring between two and 12 weeks can cause bleeding in the brain, which can be fatal. To prevent VKDB, infants must receive an injection of vitamin K1 within the first few hours after birth.
People with Malabsorption Issues
Vitamin K deficiency can occur in people with gastrointestinal disorders that affect the absorption of nutrients, such as celiac disease, ulcerative colitis, short bowel syndrome, and cystic fibrosis. It also can occur in individuals who have undergone bariatric surgery.
People Taking Certain Medications
Several types of medications can negatively affect vitamin K levels in the body:
- Antibiotics. Antibiotics are known to destroy vitamin K-producing bacteria in the gut, potentially leading to vitamin K deficiency. Unless an antibiotic is used for a prolonged period of time and vitamin K intake is poor, vitamin K supplements are usually not needed.
- Bile acid sequestrants. Bile acid sequestrants reduce cholesterol levels by preventing the reabsorption of bile acids, so they also can reduce the absorption of vitamin K. The significance of this effect is unknown. If you take cholestyramine (Questran) or colestipol (Colestid) long term, your vitamin K status should be monitored.
- Orlistat. Orlistat (Alli, Xenical) is a weight-loss drug that reduces the body’s absorption of dietary fat. Because vitamin K is a fat-soluble vitamin, orlistat interferes with its absorption, as well. The effect is generally minimal. However, some physicians may recommend taking a multivitamin supplement containing vitamin K.
Vitamin K Supplements: Do You Need Them?
There is no recommended dietary allowance for vitamin K. The U.S. Food & Drug Administration developed a daily value for vitamin K, which is 120 micrograms (mcg) for adults and children ages 4 and older. The Food and Nutrition Board (FNB) at the Institute of Medicine established an estimated adequate intake of the vitamin at all ages that starts with 2 mcg in males and females from birth to 6 months and ranges up to 120 mcg in males and 90 mcg in females ages 19 and older.
Most U.S. adults are thought to get adequate vitamin K from their diet, because vitamin K deficiency in adults is rare.
Vitamin K is included in most multivitamins and in dietary supplements as K1 (phylloquinone or phytonadione) or K2 (MK-4 or MK-7) alone or in combination with other nutrients such as calcium, magnesium, and/or vitamin D. Supplements may be useful in people with malabsorption issues or taking a medication that interferes with vitamin K absorption.
People taking warfarin should not take additional vitamin K without discussing it first with their doctor.
“You cannot get too much vitamin K from your diet, and it’s hard to get too much from taking supplements,” says Dr. Singh. “If you are not on warfarin therapy, there’s not much harm in trying a supplement, but the benefits will be very hard to determine.”
Vitamin K Safety and Side Effects
The safety and efficacy of warfarin depend on vitamin K levels in the body. Too much warfarin increases the risk of dangerous, uncontrolled bleeding. Too little warfarin may allow vitamin K to form unwanted blood clots. Consistent intake of vitamin K can help keep warfarin levels stable and prevent these issues from occurring. Note: The newer blood thinners known as direct oral anticoagulants—apixaban (Eliquis), rivaroxaban (Xarelto) and others—do not interact with vitamin K.
“We determine the dose of warfarin you need by assuming the amount of vitamin K you consume day to day and week to week remains stable,” Dr. Singh says. “This allows your anticoagulation team and pharmacy team to know the dose of warfarin you need to keep your prothrombin time (the amount of time necessary for your blood to clot) at the desired level.”
According to the Food and Nutrition Board at the Institute of Medicine, no adverse effects associated with vitamin K consumption from food or supplements have been reported in humans or animals. For this reason, no upper limit of vitamin K has been established. However, since vitamin K is a fat-soluble vitamin, and the other fat-soluble vitamins—A, D and E—are known to be toxic at certain levels, it may be unwise to overdo vitamin K, particularly since no benefit is likely to be derived from taking megadoses of the vitamin.
“The take-home is that vitamin K is promising, but we have no hard evidence that it prevents bone fractures, heart attacks, or strokes,” Dr. Singh says. “As a cardiologist, I recommend focusing on things we know make a difference, like optimizing blood pressure, blood lipids, and metabolic markers; not smoking; getting adequate exercise; and eating a healthy diet. Only then, if a patient says to me, ‘Doc, is there anything else I could do to slow the progression of coronary artery calcium, even if the benefits are theoretical?’ will I share the data on vitamin K.
“The bottom line is that we don’t know if it reduces heart attack or stroke, but it probably doesn’t increase the risk,” he continues. “However, if you are taking warfarin or have absorption issues, discuss vitamin K with your doctor before going out and buying supplements.”
