Table of Contents
Vitamin K is somewhat of an unsung hero among vitamins. We often overlook it, yet we couldn’t survive without it. Did you know that without it, even the smallest injury could cause us to bleed out? One of its main roles is blood clotting. Many people become interested in it when their doctor prescribes blood-thinning medications.
However, this is far from its only function. Today, we’ll explore other vital processes that require it, which foods are richest in vitamin K, and why Japanese people, with diets rich in fermented foods, have a lower risk of osteoporosis. [7,9]
In this article, you’ll learn about vitamin K’s impact on:
What is Vitamin K?
Vitamin K is one of the essential fat-soluble vitamins (others include vitamin D, A, and E). Compared to its counterparts, it’s often sidelined and not frequently discussed. That’s a shame because this nutrient literally helps hold our bodies together. It plays a significant role in crucial functions, such as helping maintain strong and resilient bones, and it enables our blood to clot. In practice, this means that when we get injured, the wound heals and prevents the body from losing excessive blood. [3]
You might be surprised to learn that the term vitamin K doesn’t refer to just one substance. It’s actually a group of compounds with similar structures. In nutrition, we are most interested in two main forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). To complicate matters, vitamin K2 has several subtypes, specifically MK-4, MK-7, MK-8, MK-9, and others.
There’s also vitamin K3 (menadione), but it’s not the final active form of the vitamin. Primarily, it’s an intermediate in vitamin K metabolism. [3]
What Is the Difference Between Vitamin K1 and K2?
We’ve already mentioned that these two forms of vitamin K differ in their structure. However, the key distinction lies in their origin. Additionally, one is more bioavailable and easier for the body to utilise than the other.
Vitamin K1 (Phylloquinone)
Approximately 75–90% of the vitamin K we consume comes in the form of vitamin K1, also known as phylloquinone. It is primarily found in plant-based foods, with the highest concentrations in leafy green vegetables (such as spinach, kale, cabbage, etc.). It is also present in vegetable oils and some nuts. Later on, we’ll discuss the best food sources and how much vitamin K they contain. [10]
However, this form has one major drawback—it is relatively difficult for the body to absorb. In plants, vitamin K1 is tightly bound to chloroplasts (the cell structures responsible for photosynthesis). As a result, only about 5–10% of dietary vitamin K1 is absorbed. Fortunately, pairing these foods with fats can increase absorption up to threefold. In practice, this means that drizzling your salad with a tablespoon of olive oil or sprinkling it with seeds can significantly enhance the uptake of vitamin K1. The most effective way to obtain bioavailable phylloquinone is through dietary supplements. [3,10,14]
Vitamin K2 (Menaquinone)
Menaquinone is quite unique in its origin—it is produced by bacteria, including those in our digestive system. Yes, that’s right—beneficial microorganisms that make up our gut microbiome are capable of synthesising vitamin K.
Bacteria also generate vitamin K2 during fermentation, which is why fermented foods such as natto (fermented soybeans) and pickled vegetables are excellent sources. Additionally, certain bacteria in the intestines of animals convert vitamin K1 into vitamin K2, specifically the MK-4 subtype. This is why animal-based foods can also serve as good sources of vitamin K2. [3]
Unlike vitamin K1, menaquinone is more bioavailable and better absorbed by the body. However, the absorption rate depends on the specific subtype of menaquinone—MK-7 is the most efficiently absorbed. This applies to both dietary sources and supplements, with the latter offering nearly complete absorption of the administered dose. [3,10]
Vitamin K3 (Menadione)
Despite its name, this compound is not actually a vitamin. Menadione is classified as a provitamin, meaning that it undergoes conversion in the body to become an active vitamin. Specifically, it serves as an intermediate in the process where vitamin K1 (phylloquinone) is converted into MK-4 (a type of vitamin K2). In this process, phylloquinone first transforms into menadione, which is then converted into MK-4. However, in humans, this conversion is inefficient and not well understood, whereas it appears to be more effective in animals. [3,12]
Menadione was once synthetically produced and used in dietary supplements, as researchers initially believed it could serve as an effective alternative to vitamins K1 and K2. However, it did not work as expected and even led to health complications. As a result, it is no longer used in modern dietary supplements.
A Quick Summary of Key Differences Between Forms of Vitamin K
Vitamin K1 (Phylloquinone) | Vitamin K2 (Menaquinone) | Vitamin K3 (Menadione) | |
|---|---|---|---|
| Origin | Plant-based | Bacterial / MK-4 is formed from phylloquinone conversion | Intermediate product in the conversion of vitamin K1 to K2 / Synthetic |
| Sources | Plant-based foods, dietary supplements | Fermented foods, animal-based foods, production by gut bacteria, dietary supplements | Not found in food or supplements, unsuitable for supplementation |
| Primary Functions in the Body | Blood clotting | Bone metabolism, cardiovascular health | |
| Bioavailability | Low (5–10% absorption from food, increases when consumed with fats), good absorption from supplements | Almost fully absorbed from both food and supplements | Not suitable for supplementation |
Which Form of Vitamin K Is Better?
It would certainly be easier if one form of vitamin K were more effective and beneficial so that we could focus on it in our diet. Unfortunately, that is not the case. Vitamin K1 and K2 do not function in the body in the same way, and each provides different health benefits. They complement each other perfectly, and it is important for us to get enough of both.
You might be interested in these products:
What Are the Health Benefits of Vitamin K?
We can be sure that vitamin K is not present in our bodies just by chance—it plays an essential role in many life-sustaining processes. Interestingly, each form of vitamin K has its own specialisations, focusing more on certain functions than others.
1. It Enables Blood Clotting
Vitamin K, specifically vitamin K1 (phylloquinone) and MK-4 (a type of vitamin K2), are key players in blood clotting. This process is incredibly important for our survival. When you hear “blood clotting,” you may immediately think of thrombosis and blocked arteries caused by blood clots, but these are extreme cases that occur when something goes wrong in the body.
In everyday life, blood clotting serves several crucial functions, including these important ones:
- Preventing excessive bleeding when blood vessels are damaged. Even a minor injury could cause continuous bleeding if the body were unable to form a blood clot at the wound site.
- Protecting against infections. A sealed wound prevents harmful microorganisms from entering the bloodstream.
- Promoting wound healing. The blood clot acts as a temporary barrier until the damaged tissue can regenerate. [6]
How Does Vitamin K Support Blood Clotting?
For a blood clot to form and seal a damaged blood vessel, several key steps must take place. Imagine cutting your finger—your body immediately mobilises its emergency response teams. The first action is to constrict the blood vessels to slow blood flow. At the same time, platelets rush to the site of the injury and create a temporary plug. This is where vitamin K steps in.
Vitamin K sends a signal to the clotting (coagulation) factors, instructing them to start their part of the rescue operation. Clotting factors are specialised proteins that help create a permanent plug to seal the wound. [17]
Vitamin K specifically activates four clotting factors, one of which is prothrombin. Once activated, prothrombin is converted into thrombin, which then facilitates the conversion of fibrinogen into fibrin—the primary structural component of the permanent clot. [5,12]
- In short, vitamin K activates coagulation factors, allowing the body to complete the clotting process and properly seal the wound.
How Do Blood-Thinning Medications Affect This Process?
You’ve probably heard that people taking blood thinners, particularly Warfarin, need to monitor their vitamin K intake, both from food and supplements. This is because Warfarin and vitamin K essentially work against each other. When someone needs blood thinners, it means their blood is too prone to clotting, increasing the risk of dangerous clots that could block blood vessels. To prevent this, doctors prescribe Warfarin, which reduces excessive blood clotting.
However, as we’ve already discussed, vitamin K does the opposite—it promotes clotting. If someone consumes too much vitamin K, it could interfere with the medication, making it less effective. This is why individuals on blood thinners should consult their doctor and a nutritionist about their diet and vitamin K intake. A doctor can use a prothrombin time test to measure how long it takes for blood to clot. Along with other tests, they can tailor the right treatment and monitor it over time. A nutritionist can then provide guidance on how to maintain a balanced diet while keeping vitamin K intake under control. [3]
2. Supports Bone Strength
Vitamin K is one of the essential micronutrients needed for bone growth, strength, durability, and overall health. While vitamin K1 plays the dominant role in blood clotting, vitamin K2 is more crucial for maintaining strong bones. So what exactly does this nutrient do daily to support our skeletal system?
- The body needs vitamin K for the production of osteocalcin, a protein produced by bone cells (osteoblasts). This protein promotes bone mineralisation, ensuring they remain strong and less prone to fractures. By supporting this process, vitamin K can help combat osteoporosis (bone density loss. [1]
- Vitamin K supports the growth of bone cells (osteoblasts), which contribute to bone formation and development.
- It slows down the loss of bone mass by inhibiting osteoclasts—cells responsible for breaking down bone tissue. While this process occurs naturally throughout life, it remains balanced with new bone formation until about the age of 25–30. After this point, bone loss starts to outweigh new bone growth. This makes it even more important to take care of bone health, and vitamin K helps slow down this natural decline. [1]
How Does Vitamin K Work with Calcium and Vitamin D?
When it comes to building strong, healthy bones, vitamin D and calcium play equally important roles alongside vitamin K. Calcium is the primary building block of bones, providing structural strength. However, it cannot reach the bones on its own. It needs vitamin D to facilitate calcium absorption from food and stimulate the production of osteocalcin, the protein that helps deposit calcium into bones. Once osteocalcin is produced, vitamin K steps in to activate it, allowing calcium to integrate into bone tissue. This cooperation between vitamins D and K ensures that calcium is efficiently used to strengthen bones. [2]
If you’re interested in learning more about what causes vitamin D deficiency, its other health benefits, how much you need daily, and where to get it, check out our article: Vitamin D: Why It’s So Important, What Deficiency Causes, and How to Supplement It.
3. Improves Cardiovascular Health
The role of vitamin K in heart and vascular health is often overlooked. However, vitamin K—especially in the form of menquinone —helps protect blood vessels from unwanted calcification. It activates a specific protein known as Gla-protein, which can be thought of as a guardian of the arteries. This protein prevents calcium from accumulating where it shouldn’t. By keeping blood vessels clear and flexible, vitamin K helps reduce the risk of atherosclerosis (hardening of the arteries) and other cardiovascular diseases. [4,13]
4. Other Health Benefits of Vitamin K
- Has anti-inflammatory effects, according to studies.
- It seems that it may be able to improve insulin sensitivity.
- Higher intake has been linked to a lower risk of certain cancers, according to researchers.
- May play a role in supporting cognitive functions. [1,3]
What Happens When You Have a Vitamin K Deficiency and Who Is at Risk?
After reading about its functions, you can probably already guess what happens when vitamin K levels are too low. A deficiency in this vitamin can lead to several serious health issues.
- Reduced blood clotting, leading to excessive bleeding.
- Weaker bones and lower bone density, increasing the risk of osteoporosis.
- A higher risk of atherosclerosis. [3,14]
The good news is that vitamin K deficiency is rare in healthy individuals. However, certain groups are more at risk.
Newborns – During pregnancy, vitamin K does not efficiently pass through the placenta to the baby. Additionally, breast milk contains very little vitamin K. This is why newborns are routinely given a vitamin K injection shortly after birth. An alternative is an oral supplement given over several weeks, but this may be less effective. As a result, global medical recommendations favour the injection. [8,10,11]
People with nutrient absorption disorders – Those with conditions affecting the digestive system, such as coeliac disease or inflammatory bowel disease (IBD), may struggle to absorb vitamin K properly.
Patients on long-term antibiotics – Antibiotics kill beneficial gut bacteria, which play a role in producing vitamin K.
Can Excess Vitamin K Have Undesirable Effects?
For vitamin K1 and K2, no toxic effects from excessive intake have been observed in healthy individuals. However, as previously mentioned, vitamin K can interfere with blood-thinning medications, potentially reducing their effectiveness. [3]
Which Medications Interact with Vitamin K?
When taking certain medications, vitamin K intake should be closely monitored, as it can reduce their effectiveness. Conversely, some medications can lower vitamin K levels in the body. Which ones are those?
- Warfarin and similar prescription blood thinners (vitamin K antagonists) – Vitamin K can reduce the effectiveness of these medications, leading to increased blood clotting. However, this does not apply to heparin or low-molecular-weight heparins, which do not require vitamin K restriction.
- Bile acid sequestrants, a type of cholesterol-lowering drug – These reduce bile acid absorption, which in turn affects vitamin K absorption. This can result in lower vitamin K levels in the body.
- Orlistat, a weight-loss medication – It reduces fat absorption from food. Since vitamin K is fat-soluble, this can lead to a lower intake of the vitamin.
- Antibiotics, which eliminate bacteria in the digestive system – Some antibiotics can also destroy beneficial bacteria that produce vitamin K. [16]
Where Can We Get Vitamin K?
We’ve already mentioned the main sources of vitamin K. Now, let’s take a closer look at which foods contain different forms of vitamin K, their vitamin content, and the best dietary sources.
Which Foods Are Good Sources of Vitamin K1?
In general, vitamin K1 is found in plant-based foods. Here are some of the richest sources:
- Leafy green vegetables – The highest vitamin K content is found in spinach, kale, lettuce, and cabbage. You can also use spinach or kale powder in cooking, baking, or smoothies. [10]
Cruciferous vegetables, such as broccoli.
Wild green plants, including nettles, dandelion leaves, and wild garlic.
Herbs used as seasonings, such as marjoram, basil, and savoury.
Vegetable oils – Soybean, rapeseed, and olive oil are the richest sources of vitamin K.
Fruits – Blueberries, kiwi, and grapes contain notable amounts of vitamin K. [10]
To summarise, almost any vegetable or fruit may contain some vitamin K. The same goes for oils, nuts, and seeds. However, the foods listed above have the highest concentrations. If someone needs to limit vitamin K intake, an even more detailed dietary analysis may be necessary.
The vitamin K content in food can also vary depending on age, farming methods, and climate conditions.
How Does Cooking and Sunlight Affect Vitamin K1 Content?
You might be wondering whether we unintentionally destroy some of the vitamin K in foods. If that were the case, it would be a real shame. The truth is that certain cooking methods can reduce vitamin K levels, but fortunately, there are simple ways to prevent this.
The good news is that regular cooking does not significantly destroy vitamin K in foods—or at most, only to a minimal extent. However, long-term heating at temperatures above 185°C can reduce its content. This might happen, for example, during baking. According to research, vitamin K content can decrease by about 15% if exposed to this temperature for more than 40 minutes. [10]
While heat does not have a major impact on vitamin K, it is highly sensitive to sunlight. This is especially important when it comes to oils, as they are often not stored properly. Would you believe that if an oil is exposed to daylight for just two days, its vitamin K content can drop by 46–87%? To prevent this, oils should be stored in dark containers and ideally kept in a dark place.
Vitamin K1 Content in Various Foods
Food | Vitamin K1 Content per 100 g |
|---|---|
| Rainbow chard | 830 µg |
| Spinach | 483 µg |
| Kale | 390 µg |
| Broccoli | 102 µg |
| Romaine lettuce | 83 µg |
| Marjoram (dried) | 622 µg |
| Basil (dried) | 1710 µg |
| Soybean oil | 184 µg |
| Rapeseed oil | 71 µg |
| Olive oil | 60 µg |
| Hazelnuts | 14 µg |
| Blueberries | 19 µg |
| Raspberries | 9 µg |
[18]
Which Foods Contain Vitamin K2?
As mentioned earlier, vitamin K2 has two main sources. It is produced by bacteria in our gut microbiome and can also be obtained from food.
- Fermented foods are particularly rich in vitamin K2 since they are produced through bacterial fermentation. During this process, specific beneficial microorganisms convert sugars and other nutrients into beneficial compounds, including vitamin K. However, not all bacteria produce vitamin K, so the amount depends on the strains used in fermentation.
- Vitamin K2 can be found in fermented cabbage (sauerkraut), kimchi, or kombucha. The Japanese dish natto is particularly rich in vitamin K2, and research suggests that regular consumption of natto is linked to a lower risk of osteoporosis. [7,9]
- Cheese is also a good source of vitamin K2, as it is produced through fermentation. Studies indicate that approximately half of the vitamin K2 intake in a typical mixed diet comes from cheese. [10]
- Liver and liver products contain high amounts of vitamin K2.
- Other animal products – including meat, processed meats, and eggs. Since animals also synthesise vitamin K2 in their intestines, it accumulates in their tissues. Additionally, gut bacteria in animals can convert vitamin K1 from plant-based foods into vitamin K2 (MK-4, for example). This is why chicken meat and eggs can provide this vitamin for our bodies.
Vitamin K2 Content in Various Foods
Food | Vitamin K2 Content per 100 g |
|---|---|
| Cheese and dairy products | 0.1 – 94 µg |
| Liver | 0.3 – 369 µg |
| Sauerkraut | 13 µg |
| Natto | 350 – 1000 µg |
| Chicken meat | 5.8 – 60 µg |
| Eggs | 10 – 30 µg |
[3]
Who Can Benefit from Vitamin K Supplementation?
By now, you know that newborns, people with specific health conditions, and those taking certain medications may require vitamin K supplementation. In these cases, a doctor determines the need for supplementation and ensures proper dosing. But what about healthy individuals? Who should consider taking vitamin K supplements as part of their routine?
- People with insufficient dietary intake of vitamin K – This may include vegetarians and vegans, who consume less vitamin K2, as well as those following keto diets, who may not get enough vitamin K1 due to limited fruit, vegetable, and plant-based food intake.
- Individuals with long-term low-calorie intake – A restricted diet often leads to lower overall nutrient intake.
- Athletes – Due to higher nutrient demands and increased strain on their musculoskeletal system, they may benefit from vitamin K’s role in bone health.
- Those looking to prevent osteoporosis – For this case, a combination of vitamin K2 and D3 is particularly beneficial.
- Individuals concerned about cardiovascular health.
- Postmenopausal women – This group is at a higher risk of osteoporosis.
- People taking high doses of calcium or vitamin D – Vitamin K helps balance these nutrients in the body and ensures their proper function.
What Is the Recommended Daily Intake of Vitamin K
European Food Safety Authority (EFSA):
- 70 µg for healthy adults, including pregnant and breastfeeding women
German Nutrition Society (DACH):
- 70 µg for men
- 60 µg for women, including pregnant and breastfeeding women [3,15]
For simplicity, these recommended values are based on phylloquinone (vitamin K1). However, in practice, the total vitamin K intake also includes menaquinones (vitamin K2).
If you’re curious about the effects and benefits of other vitamins, check out our article The Complete Guide to Vitamins: Their Functions, Deficiency Symptoms, and Recommended Intake.
What is the lesson?
Vitamin K may not get as much attention as vitamins D or C, but it plays a vital role in our bodies, particularly in blood clotting, bone health, and vascular protection. Ensuring adequate intake of both K1 and K2 is essential for optimal health. The best way to obtain vitamin K is through a balanced and varied diet. Leafy green vegetables provide vitamin K1, while fermented foods and animal products supply vitamin K2. If needed, supplements can help maintain healthy levels, allowing you to fully benefit from this essential vitamin.
Vitamin K is essential—spread the word! Don’t keep this information to yourself—share it with your friends and family so they can also learn about the benefits of vitamin K!
[1] AKBARI, S. - RASOULI-GHAHROUDI, A.A. Vitamin K and Bone Metabolism: A Review of the Latest Evidence in Preclinical Studies. https://pubmed.ncbi.nlm.nih.gov/30050932/][
[2] BALLEGOOIJEN, A.J. VAN et al. The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review. – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5613455/
[3] EFSA PANEL ON DIETETIC PRODUCTS, NUTRITION AND ALLERGIES (NDA) et al. Dietary reference values for vitamin K. – https://data.europa.eu/doi/10.2903/j.efsa.2017.4780
[4] HARIRI, E. et al. Vitamin K2-a neglected player in cardiovascular health: a narrative review. – https://pubmed.ncbi.nlm.nih.gov/34785587/
[5] HARUTYUNYAN, H.A. Prothrombin and fibrinogen carbonylation: How that can affect the blood clotting. – https://pmc.ncbi.nlm.nih.gov/articles/PMC6837719/
[6] HOU, Y. et al. Platelets in hemostasis and thrombosis: Novel mechanisms of fibrinogen-independent platelet aggregation and fibronectin-mediated protein wave of hemostasis. – https://pubmed.ncbi.nlm.nih.gov/26541706/
[7] IKEDA, Y. et al. Intake of Fermented Soybeans, Natto, Is Associated with Reduced Bone Loss in Postmenopausal Women: Japanese Population-Based Osteoporosis (JPOS) Study1. – https://www.sciencedirect.com/science/article/pii/S0022316622082499
[8] JULLIEN, S. Vitamin K prophylaxis in newborns. – https://pmc.ncbi.nlm.nih.gov/articles/PMC8424792/
[9] KOJIMA, A. et al. Natto Intake is Inversely Associated with Osteoporotic Fracture Risk in Postmenopausal Japanese Women. – https://jn.nutrition.org/article/S0022-3166(22)02079-X/fulltext
[10] MLADĚNKA, P. et al. Vitamin K – sources, physiological role, kinetics, deficiency, detection, therapeutic use, and toxicity. – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8907489/
[11] LOEWY, A.D. Position Statement: Guidelines for vitamin K prophylaxis in newborns: A joint statement of the Canadian Paediatric Society and the College of Family Physicians of Canada. – https://pmc.ncbi.nlm.nih.gov/articles/PMC6184976/
[12] SHEARER, M.J. - OKANO, T. Key Pathways and Regulators of Vitamin K Function and Intermediary Metabolism. – https://pubmed.ncbi.nlm.nih.gov/29856932/
[13] SCHWALFENBERG, G.K. Vitamins K1 and K2: The Emerging Group of Vitamins Required for Human Health. – https://pubmed.ncbi.nlm.nih.gov/28698808/
[14] VERMEER, C. Vitamin K: the effect on health beyond coagulation – an overview. – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3321262/
[15] Dietary Reference Values | DRV Finder. – https://multimedia.efsa.europa.eu/drvs/index.htm
[16] Office of Dietary Supplements - Vitamin K. – https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
[17] Physiology, Clotting Mechanism - StatPearls - NCBI Bookshelf. – https://www.ncbi.nlm.nih.gov/books/NBK507795/
[18] FoodData Central. – https://fdc.nal.usda.gov/
Add a comment