Vitamin K is a nutrient well known for its essential role in blood clotting, but it also impacts a range of bodily functions, including cardiovascular and cognitive health. It comes in two forms, vitamin K1 and vitamin K2—the latter of which may play a bigger role in bone health. And while both forms of vitamin K are present in foods, those food sources differ.
Here’s what you need to know about vitamin K2, including how it differs from vitamin K1, the role it plays in the body and common food sources.
What Is Vitamin K2?
Vitamin K, a fat-soluble vitamin, refers to a group of compounds including vitamin K1 (or phylloquinone) and a range of vitamin K2 forms (menaquinones).
“While both forms are important, they differ in their sources,” says Akil Palanisamy, M.D., a California-based integrative medicine physician, department chair for integrative medicine at the Sutter Health Institute for Health and Healing and author of The TIGER Protocol: An Integrative, 5-Step Program to Treat and Heal Your Autoimmunity. “With increasing research about the health benefits of vitamin K2, it’s starting to garner more interest.”
Menaquinones are types of vitamin K2 found in animal products and fermented foods. Most menaquinones are also produced by bacteria in the human gut. Menaquinones vary in length from four to 13 units. The number of units is denoted by the number after MK, so MK-4 has four units, MK-5 has five units and so on. The most well-researched menaquinones are MK-4, MK-7 and MK-9.
“It’s been suggested that vitamin K2, with its longer half-life compared to vitamin K1, travels throughout the body and plays a larger role in bone, cartilage and soft tissue,” says Jacqueline Wyman, a New York City-based private practice registered dietitian. The half-life of a nutrient measures how long it takes for half of a nutrient to be removed from the body through metabolism and excretion.
Benefits of Vitamin K2
Researchers have studied vitamin K2 in the following areas.
Bone Health
“Vitamin K2 activates osteocalcin, a protein that helps bind calcium to the bone matrix, contributing to bone mineralization and strength,” says Dr. Palanisamy. Indeed, a 2022 Frontiers in Public Health systematic review and meta-analysis concluded that vitamin K2 can help prevent and treat osteoporosis in postmenopausal women by indirectly promoting bone mineralization and bone strength.
Vitamin K2 may be even more effective when used in combination with other treatments such as vitamin D, calcium or alendronate, research suggests. The Frontiers in Public Health review also suggests that vitamin K2 may help prevent fractures, but more research is needed to confirm this finding.
Cardiovascular Health
“Vitamin K2 may play a role in cardiovascular health by helping to prevent arterial calcification, which is the accumulation of calcium in the arteries,” says Dr. Palanisamy. Calcification, or hardening of the heart arteries, is a contributor to heart disease. “By activating a protein called matrix Gla protein, vitamin K2 helps inhibit calcium deposits,” he adds. This is echoed in a 2022 Frontiers in Pharmacology review summarizing vitamin K2’s health benefits.
However, a 2022 randomized clinical trial in Circulation of elderly men with aortic valve calcification showed that taking vitamin K2 and vitamin D supplementation for two years did not influence the progression of the calcification.
Additionally, in a 2023 American Journal of Transplantation randomized controlled trial involving kidney transplant recipients, researchers concluded that taking vitamin K2 supplementation (in the form of MK-7) didn’t change the likeliness of blood calcification, but it did help slow down the hardening of the arteries. Research on the impact of vitamin K2 on cardiovascular health is ongoing.
Brain Health
“Vitamin K2 may also impact brain health,” says Sharon Puello, a New York-based registered dietitian and adjunct professor at City University of New York. She cites a 2022 Alzheimer’s and Dementia study examining the association of vitamin K with cognitive health in over 300 elderly participants. Participants with higher brain MK-4 (a form of vitamin K2) concentrations had a 17% to 20% lower risk of developing dementia or mild cognitive impairment.
Antidepressant Effect in Individuals With PCOS
In other recent research, a small 2022 study in BMC Women’s Health found that taking vitamin K2 (MK-7) for eight weeks significantly improved depression in women with polycystic ovary syndrome (PCOS). This was the first study to investigate this relationship, according to the researcher.
Sources of Vitamin K2
“Vitamin K2 is found in animal products and fermented foods,” says Wyman.
However, the more common form of dietary vitamin K is largely vitamin K1. “Approximately 90% of vitamin K [in the] American diet is vitamin K1, obtained from green leafy vegetables (such as kale, broccoli and spinach) and some plant oils like soybean and canola,” says Wyman.
Food databases like the U.S. Department of Agriculture’s FoodData Central have limited information about vitamin K2 content in foods. However, researchers have evaluated the amount of vitamin K2 in some foods, as shown in the following table.
FOOD SOURCE | SERVING SIZE | AMOUNT OF K2 | RDA—PERCENT OF RECOMMENDED DAILY ALLOWANCE OF VITAMIN K FOR ADULTS (90 TO 120 MICROGRAMS) |
| Natto (Japanese fermented soybean-based product) | 3.5 ounces | 998 micrograms | 1,109% to 832% |
Eel | 3.5 ounces | 63.1 micrograms | 53% to 70% |
Hard cheese | 1 ounces | 14.6 micrograms | 12% to 16% |
Soft cheese | 1 ounces | 11.3 micrograms | 9% to 13% |
Beef liver | 3.5 ounces | 11.2 micrograms | 9% to 12% |
Chicken meat | 3.5 ounces | 10.1 micrograms | 8% to 11% |
Minced meat | 3.5 ounces | 7.6 micrograms | 6% to 8% |
“It’s difficult to determine the amount of vitamin K2 in food because there are inconsistencies in types of animal feed, fat content and bacterial growth,” says Wyman. “It’s best to consume a diet with a wide variety of foods that contain both vitamins K1 and K2.”
How Much Vitamin K Do You Need?
Puello notes that current vitamin K recommendations are non-specific, and cites a 2020 Nutrients article that suggests setting a separate recommended daily intake for vitamin K.
The following table shows the adequate intake levels for vitamin K, in micrograms:
AGE | MALE | FEMALE | PREGNANCY | LOCATION |
1 to 3 years | 30 | 30 | - | - |
4 to 8 years | 55 | 55 | - | - |
9 to 13 years | 60 | 60 | - | - |
14 to 18 years | 75 | 75 | 75 | 75 |
19+ years | 120 | 90 | 90 | 90 |
Symptoms of Vitamin K2 Deficiency
Inadequate vitamin K2 intake is more common than vitamin K1 since most people in the U.S. get enough vitamin K1 from foods, says Dr. Palanisamy. The research indicates that, “suboptimal vitamin K2 intake can contribute to increased risk of osteoporosis, fractures, coronary arterial calcification, heart disease and dental issues,” he adds.
Vitamin K Precautions
“[People] on blood thinner medications should avoid vitamin K supplements unless advised to take them by their health care practitioner,” says Puello. Other medications that can interact with vitamin K supplements include antibiotics and medications that help lower cholesterol by binding to bile acid, such as cholestyramine. Always consult your health care provider before adding a supplement to your routine.
“When it comes to vitamin K supplements, a toxic level hasn’t been identified,” says Puello. “Meaning, unless you’re taking an extremely high dose frequently, there isn’t likely to be a downside to supplementation. In the rare case that toxicity develops, it would typically present as jaundice (yellowed skin), elevated liver enzymes and hemolytic anemia (shortened red blood cell life span).”
Always follow directions as indicated by the supplement manufacturer or as prescribed by your doctor.