Vitamin K1 and K2 belong to the same vitamin family, but they come from different foods and behave differently in the body. Leafy green vegetables supply most dietary K1. K2 includes several forms, such as MK-4 and MK-7, which occur in certain animal and fermented foods. K2 attracts interest for bone and heart health, but current evidence does not show that every healthy adult needs a K2 supplement.
Key Takeaways
- Vitamin K1 is phylloquinone. Vitamin K2 includes menaquinones such as MK-4 and MK-7.
- Leafy greens provide large amounts of K1. Fermented and animal foods can provide K2.
- Both forms help the body activate proteins involved in normal clotting and other functions.
- K2 research for bone and cardiovascular health is promising in some areas, but important questions remain.
- Warfarin users should not make major changes to vitamin K intake without medical guidance.
What Is the Difference Between K1 and K2?
Vitamin K describes a family of fat-soluble compounds. The two groups people discuss most often are K1 and K2.
Scientists call vitamin K1 phylloquinone. Plants produce this form, so green vegetables provide much of the K1 in a typical diet.
Vitamin K2 refers to a group called menaquinones. Researchers label these forms MK-4 through MK-13 according to their chemical side chains. MK-4 and MK-7 appear often in dietary supplements.
A useful way to think about it: K1 is one major form. K2 is a group of related forms. That difference matters when you compare foods, supplements, or research studies.
Vitamin K1 vs K2 at a Glance
| Feature | Vitamin K1 | Vitamin K2 |
|---|---|---|
| Name | Phylloquinone | Menaquinones |
| Common forms | K1 | MK-4, MK-7, MK-8, MK-9 and others |
| Main food sources | Leafy greens and some vegetable oils | Natto, some cheeses, eggs, meat, and other fermented foods |
| Common supplement forms | Phylloquinone | MK-4 or MK-7 |
| Role in vitamin K activity | Active | Active |
What Does Vitamin K Do?
Your body uses vitamin K to activate several proteins. Some of these proteins help blood clot normally. Others take part in bone metabolism and other processes.
For example, bone contains a vitamin K-dependent protein called osteocalcin. Another protein, matrix Gla protein, helps regulate mineral buildup in tissues.
These roles explain why researchers study vitamin K in relation to bones and blood vessels. Still, a biological role does not prove that extra K2 will prevent fractures or heart disease.
Best Food Sources of Vitamin K1
Green vegetables make K1 easy to obtain through food. NIH lists leafy vegetables among the main dietary sources of vitamin K.
- Kale
- Spinach
- Collard greens
- Broccoli
- Brussels sprouts
- Soybean and canola oils
Since vitamin K dissolves in fat, eating these foods with some dietary fat can support absorption.
Best Food Sources of Vitamin K2
K2 appears in a smaller range of foods. Bacteria produce many menaquinones, so fermented foods can contain meaningful amounts.
- Natto: a fermented soybean food known for its MK-7 content.
- Cheese: certain varieties contain several menaquinones.
- Eggs: can contribute small amounts of MK-4.
- Meat and poultry: may provide MK-4 and other forms.
- Fermented foods: K2 content varies with the bacteria and production method.
Food databases track K1 more completely than individual K2 forms. As a result, calculating an exact daily K2 intake can be difficult.
MK-4 vs MK-7
Many K2 supplements use MK-4 or MK-7. Both belong to the K2 family, but they do not behave exactly the same way.
MK-4
Human and animal tissues can produce MK-4 from other forms of vitamin K. Some animal foods also contain it. MK-4 leaves the bloodstream relatively quickly compared with longer-chain forms.
MK-7
Natto contains large amounts of MK-7, and supplement companies often use this form. MK-7 stays in circulation longer than K1 and MK-4.
Longer does not automatically mean better: A longer time in the bloodstream can change how a nutrient affects certain markers. Researchers still need clinical studies to show whether that difference improves long-term health outcomes.
Is K2 Better for Bone Health?
Scientists continue to study K2 because vitamin K helps activate osteocalcin, a protein involved in bone metabolism.
A 2022 review of randomized trials in postmenopausal women found improvements in some bone mineral density measures with K2. Fracture results were less consistent and changed when researchers removed a study that differed from the others.
A 2025 review also found that K2 changed several markers related to bone turnover in women with postmenopausal osteoporosis. The authors still called for longer studies to confirm meaningful clinical benefits.
What this means: K2 may influence bone-related markers, and some trials suggest benefits for bone density. The evidence does not support using K2 as a replacement for osteoporosis screening, exercise, adequate nutrition, or prescribed treatment.
Does K2 Protect the Heart?
K2 supplements often come with claims about keeping calcium out of the arteries. Those claims simplify a much more complex area of research.
Vitamin K activates matrix Gla protein, which helps regulate mineral buildup in tissues. That mechanism gives researchers a reason to study K1 and K2 in vascular health.
A 2023 meta-analysis of 14 randomized trials found that vitamin K supplementation slowed coronary artery calcification in pooled results and lowered a marker of inactive matrix Gla protein. However, the researchers called for stronger trials before drawing firm conclusions.
Results become even less certain in specific groups. A separate review in people with chronic kidney disease did not find solid evidence that vitamin K supplements prevent vascular calcification.
Do not turn a research signal into a promise: Current studies do not prove that K2 supplements prevent heart attacks, strokes, or cardiovascular disease.
How Much Vitamin K Do Adults Need?
U.S. nutrition guidelines use an Adequate Intake for vitamin K. Experts use this type of target when available evidence does not support a formal Recommended Dietary Allowance.
- Men age 19 and older: 120 micrograms per day.
- Women age 19 and older: 90 micrograms per day.
These targets apply to total vitamin K intake. The United States does not set a separate daily requirement for K2, MK-4, or MK-7.
Do You Need a K2 Supplement?
Most healthy adults do not receive a general recommendation to take K2 supplements. Adults rarely develop clinically important vitamin K deficiency when they eat a varied diet and absorb fat normally.
Some people face a higher risk of low vitamin K status. Conditions that reduce fat absorption can interfere with vitamin K absorption. Certain medications can also affect vitamin K activity or levels.
If you want K2 for bone or cardiovascular health, first identify the goal. Then compare that goal with the quality of evidence for the specific K2 form and dose.
Do You Need K2 With Vitamin D3?
Supplement companies frequently combine vitamin D3 with K2. Both nutrients play roles in bone and calcium metabolism, which makes the pairing easy to market.
That does not mean every person who takes vitamin D3 also needs a K2 supplement. Your vitamin D needs and vitamin K needs are separate questions.
Check combination products: Look at the exact K2 form, dose, vitamin D amount, and other ingredients. A combination product offers convenience, not proof that everyone needs both nutrients together.
Vitamin K and Warfarin
Vitamin K can interact seriously with warfarin and other vitamin K-antagonist drugs. These medicines work by reducing vitamin K activity.
A sudden increase or decrease in vitamin K intake can change the effect of warfarin. NIH therefore advises people who use these medicines to keep vitamin K intake consistent.
If you take warfarin: Do not start, stop, or substantially change K1, MK-4, or MK-7 supplements without speaking with the healthcare professional who manages your anticoagulant treatment.
How to Choose a Vitamin K Supplement
If a vitamin K supplement fits your needs, read the Supplement Facts panel instead of relying on front-label claims.
- Identify the form: Look for K1, MK-4, MK-7, or a combination.
- Check the amount: A larger dose does not automatically provide a better result.
- Know your goal: Match the supplement to a specific reason rather than a broad wellness claim.
- Review other products: Multivitamins and vitamin D supplements may already contain vitamin K.
- Check medications: This step matters most for people who use warfarin or another vitamin K antagonist.
K1 or K2: Which Is Better?
K1 is not an inferior version of vitamin K. It supplies much of the vitamin K in the diet and supports essential functions in the body.
K2 forms have different properties. MK-7, for example, stays in circulation longer. Research also links K2 supplementation with changes in some bone and vascular markers.
Still, current evidence does not make K2 a universal winner. For most healthy adults, a food-first approach remains a sensible starting point.
Frequently Asked Questions
U.S. supplement regulation: FDA does not approve dietary supplements for safety and effectiveness before they are sold. Manufacturers are responsible for product safety and truthful labeling; discuss supplements with a healthcare professional when medications, pregnancy, breastfeeding, chronic disease, or planned surgery may affect suitability.
The Bottom Line
Vitamin K1 and K2 both contribute to vitamin K activity. Leafy green vegetables provide most dietary K1, while fermented and animal foods can provide K2 forms such as MK-4 and MK-7. These forms differ in how the body handles them, but those differences do not make K1 inferior.
K2 research for bone and vascular health remains active. Some results look promising, yet major clinical benefits still need stronger confirmation. Focus first on a varied diet and use supplements for a clear reason. Seek professional guidance when medications, especially warfarin, affect vitamin K management.
Medical disclaimer
Medical disclaimer: This content is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Dietary needs and supplement suitability vary by individual.
Sources
- National Institutes of Health, Office of Dietary Supplements. Vitamin K: Health Professional Fact Sheet. Accessed September 2026.
- Zhang Z, Li Y, Li J, et al. The Effect of Vitamin K2 Supplementation on Bone Turnover Biochemical Markers in Postmenopausal Osteoporosis Patients: A Systematic Review and Meta-analysis. Frontiers in Endocrinology. 2025;16:1703116.
- Ma ML, Ma C, He J, et al. Efficacy of Vitamin K2 in the Prevention and Treatment of Postmenopausal Osteoporosis: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Frontiers in Public Health. 2022;10:979649.
- Li T, Wang Y, Tu WP. Vitamin K Supplementation and Vascular Calcification: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Frontiers in Nutrition. 2023;10:1115069.
- Geng C, Huang L, Pu L, Feng Y. Effects of Vitamin K Supplementation on Vascular Calcification in Chronic Kidney Disease: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Frontiers in Nutrition. 2023;9:1001826.
