Vitamin K1 vs K2: Understanding the Key Differences and Health Benefits

When it comes to essential nutrients, vitamin K often takes a backseat to more well-known vitamins like C or D. However, this fat-soluble vitamin plays crucial roles in numerous bodily functions, from blood clotting to bone mineralization. What many people don’t realize is that vitamin K isn’t just one compound—it exists in multiple forms, with vitamin K1 and K2 being the most significant for human health.

Understanding the differences between vitamin K1 and K2 can help you make informed dietary choices and potentially improve your overall health outcomes. While both forms share similar chemical structures and some overlapping functions, they differ substantially in their food sources, absorption rates, and specific health benefits.

What Exactly Is Vitamin K?

Vitamin K is a family of fat-soluble compounds that share a common chemical structure called a quinone ring. The discovery of vitamin K dates back to the early 20th century when researchers noticed that certain diets led to prolonged bleeding in animals. This led to the identification of a “coagulation vitamin,” which was later named vitamin K (from the German word “Koagulation”).

The vitamin K family consists of several compounds, but two are particularly important in human nutrition:

• Vitamin K1 (Phylloquinone): The most common dietary form, primarily synthesized by plants
• Vitamin K2 (Menaquinone): A group of related compounds produced by bacteria and found in fermented foods and animal products

Both forms are essential for activating specific proteins that regulate critical biological processes, but they accomplish these tasks in different ways and with varying degrees of effectiveness.

Vitamin K1: The Plant-Based Form

Primary Food Sources of Vitamin K1

Vitamin K1 represents approximately 75-90% of total vitamin K intake in typical Western diets. It’s predominantly found in green, leafy vegetables and some vegetable oils. The highest concentrations are found in:

• Kale: One of the richest sources, providing over 1,000 mcg per cooked cup
• Collard greens: Another exceptional source with similar levels to kale
• Spinach: Contains approximately 890 mcg per cooked cup
• Turnip greens: Offers around 530 mcg per cooked cup
• Broccoli: Provides about 220 mcg per cooked cup
• Brussels sprouts: Contains roughly 220 mcg per cooked cup
• Asparagus: A moderate source with about 90 mcg per cooked cup
• Green beans: Offers approximately 60 mcg per cooked cup

Other sources include vegetable oils like soybean, canola, and olive oil, though in smaller amounts. Herbs like parsley and basil also contain significant amounts when consumed fresh.

Absorption Characteristics of K1

One significant limitation of vitamin K1 is its relatively poor bioavailability. Research indicates that less than 10% of the K1 consumed from plant sources is actually absorbed by the body. This low absorption rate is due to K1 being tightly bound to the chloroplast membranes in plant cells.

However, consuming vitamin K1 with dietary fats can significantly enhance absorption. This is why eating your leafy greens with olive oil, nuts, or avocado can help maximize the vitamin K1 your body actually utilizes.

Vitamin K2: The Bacterial and Animal-Based Form

Understanding K2 Subtypes

Unlike K1, which exists as a single compound, vitamin K2 comprises several subtypes known as menaquinones, designated as MK-4 through MK-13 based on the length of their side chains. The most important subtypes for human health are:

• MK-4: Found in animal products and is the only K2 form not produced by bacteria
• MK-7: Produced by bacteria, particularly abundant in fermented foods
• MK-8 and MK-9: Found in certain cheeses
• MK-10 through MK-13: Present in various fermented foods

Primary Food Sources of Vitamin K2

The best dietary sources of vitamin K2 include:

• Natto (fermented soybeans): The undisputed champion, containing over 1,000 mcg per 3.5-ounce serving, primarily as MK-7
• Goose liver: Contains approximately 370 mcg per 3.5 ounces
• Hard cheeses (Gouda, Edam, aged cheddar): Provide 50-80 mcg per 3.5 ounces
• Soft cheeses (Brie, blue cheese): Contain about 55-60 mcg per 3.5 ounces
• Egg yolks: Offer roughly 30-35 mcg per 3.5 ounces
• Chicken (dark meat): Provides approximately 60 mcg per 3.5 ounces
• Butter from grass-fed cows: Contains about 15 mcg per 3.5 ounces
• Sauerkraut: A fermented food providing modest amounts of K2

Superior Absorption of K2

Vitamin K2 appears to have better bioavailability than K1 for several reasons. First, K2 is typically found in foods that contain fat, which enhances absorption since vitamin K is fat-soluble. Second, K2 isn’t bound to plant fiber, making it more readily available for absorption.

Additionally, the longer side chains of certain K2 forms (particularly MK-7) allow them to remain in circulation much longer than K1. While K1 may stay in the bloodstream for just a few hours, MK-7 can circulate for several days, allowing for better distribution to various tissues throughout the body.

How K1 and K2 Work Differently in Your Body

Distribution and Utilization Patterns

One of the most significant differences between K1 and K2 lies in how they’re distributed and utilized after absorption:

Vitamin K1 Distribution: K1 is rapidly taken up by the liver, where it’s used primarily for synthesizing blood clotting factors. The liver tends to monopolize available K1, meaning other tissues receive relatively little. This makes K1 particularly important for maintaining proper coagulation function.

Vitamin K2 Distribution: K2, especially the longer-chain menaquinones like MK-7, circulates throughout the body for extended periods and is distributed more evenly to various tissues including bones, blood vessels, and soft tissues. This broader distribution pattern may explain why K2 appears particularly important for bone and cardiovascular health.

Protein Activation Functions

Both forms of vitamin K work by activating specific proteins through a process called carboxylation. These vitamin K-dependent proteins (VKDPs) include:

• Clotting factors: Proteins essential for blood coagulation
• Osteocalcin: A protein that binds calcium in bones and teeth
• Matrix Gla protein (MGP): A protein that prevents calcium from depositing in soft tissues like arteries
• Protein S: Another anticoagulant protein

While both K1 and K2 can activate these proteins, their different distribution patterns mean they may be more or less effective for specific functions.

Blood Clotting: Essential for Proper Coagulation

The most well-established function of vitamin K is its critical role in blood clotting. Without adequate vitamin K, your blood wouldn’t clot properly, leading to excessive bleeding from even minor injuries.

Vitamin K enables the production of several clotting factors in the liver, including prothrombin (Factor II), and Factors VII, IX, and X. When you get a cut or injury, these factors work together in a cascade reaction to form blood clots and stop bleeding.

K1 vs K2 for Clotting Function

Vitamin K1 is generally considered the primary form responsible for maintaining healthy blood clotting, primarily because it’s preferentially used by the liver where clotting factors are produced. However, K2 can also contribute to clotting factor production, particularly when K1 intake is low.

An interesting study on natto consumption demonstrated that this K2-rich food significantly affected blood clotting measures for up to four days after consumption, showing a much more prolonged effect than K1-rich foods. This suggests that while K1 may be more immediately effective for clotting, K2’s longer circulation time can provide sustained support.

Important Considerations for Medication Users

If you’re taking blood-thinning medications that work by interfering with vitamin K (such as certain anticoagulants), it’s essential to maintain consistent vitamin K intake from both K1 and K2 sources. Sudden increases or decreases in dietary vitamin K can affect how well these medications work. Always consult with your healthcare provider before making significant dietary changes or taking vitamin K supplements if you’re on anticoagulant therapy.

Bone Health: Building and Maintaining Strong Bones

Beyond blood clotting, vitamin K plays a vital role in bone metabolism by activating osteocalcin, a protein that helps bind calcium to the bone matrix. Without sufficient vitamin K, osteocalcin remains inactive, and calcium cannot be properly incorporated into bone tissue.

Research on K1 and Bone Health

Several observational studies have found associations between higher vitamin K1 intake and reduced fracture risk. However, controlled intervention trials using K1 supplements have produced mixed results, with many showing minimal or no effect on bone density or fracture rates.

This inconsistency might be explained by K1’s preferential accumulation in the liver rather than in bone tissue, potentially limiting its effectiveness for skeletal health.

Research on K2 and Bone Health

Vitamin K2, particularly the MK-4 and MK-7 forms, has shown more promising results in some studies related to bone health. Several Japanese studies found that MK-4 supplementation reduced fracture rates in postmenopausal women and people with osteoporosis.

The MK-7 form has also demonstrated positive effects in some research, improving bone mineral density and bone strength markers. Its longer half-life in the bloodstream may allow for better delivery to bone tissue compared to K1.

However, it’s important to note that not all studies have shown benefits, and more high-quality research is needed. The European Food Safety Authority has acknowledged vitamin K’s role in maintaining normal bone health, but optimal dosing and the superiority of one form over another remain topics of ongoing investigation.

Cardiovascular Health: Protecting Your Heart and Arteries

One of the most exciting areas of vitamin K research involves its potential role in cardiovascular health, particularly in preventing arterial calcification.

The Calcium Paradox

As we age, calcium can accumulate in our arteries while simultaneously being lost from our bones—a phenomenon sometimes called the “calcium paradox.” This arterial calcification contributes to atherosclerosis and significantly increases the risk of heart disease and stroke.

Vitamin K2 activates matrix Gla protein (MGP), which acts like a calcium traffic controller, preventing calcium from depositing in arterial walls while helping direct it to bones and teeth where it belongs.

Observational Evidence

Several large observational studies have suggested that higher vitamin K2 intake is associated with reduced arterial calcification and lower risk of heart disease. One landmark study, the Rotterdam Study, found that participants with the highest K2 intake had a 57% lower risk of dying from heart disease compared to those with the lowest intake. Interestingly, vitamin K1 intake showed no such association.

Another study found that each additional 10 mcg of K2 consumed per day was associated with a 9% reduction in coronary heart disease risk.

Intervention Studies

More recent controlled trials have investigated whether vitamin K supplementation can actually improve cardiovascular health markers. Some studies using MK-7 supplements have shown improvements in arterial stiffness and reductions in arterial calcification progression, particularly in people at high risk.

Research on vitamin K1 supplementation has produced more mixed results, though some studies have shown benefits, particularly at higher doses.

While these findings are encouraging, more long-term, high-quality studies are needed to definitively establish whether vitamin K supplementation can prevent cardiovascular events like heart attacks and strokes.

Other Potential Health Benefits

Brain Health

Emerging research suggests vitamin K may play a role in brain health. Vitamin K-dependent proteins are found in brain tissue, and some studies have linked higher vitamin K intake with better cognitive function and lower risk of dementia. However, this research is still in early stages.

Metabolic Health

Some studies indicate that vitamin K2 may help improve insulin sensitivity and reduce diabetes risk, though results have been inconsistent. The mechanism may involve K2’s effects on osteocalcin, which appears to influence insulin secretion and sensitivity.

Cancer Prevention

Limited research has suggested that vitamin K2 might have anti-cancer properties, particularly for liver and prostate cancers. However, evidence is preliminary and insufficient to make definitive recommendations.

Vitamin K Deficiency: Risks and Symptoms

Who’s at Risk?

True vitamin K deficiency is uncommon in healthy adults but can occur in certain situations:

• Newborn infants: Babies are born with low vitamin K stores and limited intestinal bacteria, putting them at risk for vitamin K deficiency bleeding
• People with malabsorption disorders: Conditions like celiac disease, Crohn’s disease, ulcerative colitis, and cystic fibrosis can impair fat absorption, including fat-soluble vitamins like K
• Those with liver disease: Since the liver stores vitamin K and produces clotting factors, liver disorders can lead to functional deficiency
• People taking certain medications: Some antibiotics and anticoagulants can interfere with vitamin K function or production
• Individuals with very low dietary intake: Those who consume few vegetables and fermented foods may have inadequate intake

Signs and Symptoms

The primary symptom of vitamin K deficiency is excessive bleeding, which may manifest as:

• Easy bruising
• Heavy menstrual bleeding
• Blood in urine or stool
• Bleeding gums
• Nosebleeds
• Prolonged bleeding from cuts or wounds

If you experience any of these symptoms, consult a healthcare provider for proper evaluation and testing.

Subclinical Deficiency

More concerning than outright deficiency is the possibility of subclinical insufficiency—having enough vitamin K to maintain normal blood clotting but not enough to optimally support bone and cardiovascular health. This condition doesn’t cause obvious symptoms but may contribute to long-term health problems.

Some researchers estimate that a significant portion of the population may have subclinical vitamin K insufficiency, particularly regarding K2, which is less abundant in typical Western diets.

Recommended Intake and Dietary Guidelines

Official Recommendations

The adequate intake (AI) for vitamin K, based primarily on K1, is:

• Adult men: 120 mcg per day
• Adult women: 90 mcg per day
• Pregnant and lactating women: 90 mcg per day

These recommendations are set at levels sufficient to maintain normal blood clotting, but some experts believe higher intakes may be beneficial for bone and cardiovascular health.

No Official K2 Recommendations

Currently, there are no specific dietary recommendations for vitamin K2 intake. This is partly because research is still emerging and partly because it’s difficult to accurately measure K2 content in foods. Some experts suggest aiming for 45-185 mcg of K2 daily based on the amounts used in successful research studies.

How to Optimize Your Vitamin K Intake

Strategies for Getting Enough K1

1. Eat leafy greens daily: Just one cup of cooked kale or spinach exceeds the daily AI for vitamin K
2. Add greens to every meal: Include spinach in omelets, add kale to smoothies, or put mixed greens on sandwiches
3. Don’t overcook vegetables: While some cooking can actually increase K1 availability by breaking down plant cell walls, excessive cooking can degrade the vitamin
4. Pair with healthy fats: Drizzle olive oil on salads, add avocado to green smoothies, or cook greens with butter to enhance absorption
5. Try green herbs: Parsley, cilantro, and basil are concentrated sources when used fresh

Strategies for Getting Enough K2

1. Try natto: If you can acquire a taste for this traditional Japanese food, just one small serving provides several days’ worth of K2. It has a strong flavor and slimy texture that takes getting used to, but it’s nutritionally unmatched
2. Choose grass-fed animal products: Animals raised on pasture produce meat, eggs, and dairy with significantly more K2 than conventionally raised animals
3. Enjoy fermented cheeses: Gouda, Edam, aged cheddar, and blue cheese are particularly good sources. The longer the aging process, generally the higher the K2 content
4. Eat egg yolks: Don’t skip the yolks—they contain most of the egg’s K2 along with other fat-soluble vitamins
5. Choose dark meat poultry: Chicken thighs and legs contain more K2 than breast meat
6. Include fermented vegetables: Sauerkraut and other fermented vegetables provide modest amounts of K2 along with beneficial probiotics
7. Consider grass-fed butter or ghee: These traditional fats contain K2 and can be used in cooking to add flavor and nutrition

Sample Daily Meal Plan for Optimal Vitamin K

Breakfast: Omelet with spinach and cheese, cooked in butter
K1: ~450 mcg, K2: ~20 mcg

Lunch: Salad with mixed greens, chicken thigh, and olive oil dressing
K1: ~250 mcg, K2: ~30 mcg

Snack: Hard cheese with crackers
K2: ~25 mcg

Dinner: Roasted Brussels sprouts with a small serving of natto (if tolerated)
K1: ~220 mcg, K2: ~200+ mcg

This sample day provides ample amounts of both K1 and K2 from diverse, whole food sources.

Should You Take Vitamin K Supplements?

Types of Supplements Available

Vitamin K supplements come in several forms:

• K1 (phylloquinone): Usually derived from plants
• K2 as MK-4: Typically synthetic
• K2 as MK-7: Usually derived from natto fermentation
• Mixed forms: Containing both K1 and K2

Who Might Benefit from Supplements?

Supplementation might be appropriate for:

• People with malabsorption conditions
• Those who consume very few vegetables or fermented foods
• Individuals at high risk for osteoporosis or cardiovascular disease
• People following certain restrictive diets
• Older adults who may have reduced K2 production by gut bacteria

Safety and Dosing Considerations

Vitamin K has no established upper intake level because it appears to have very low toxicity. However, this doesn’t mean supplements are appropriate for everyone.

Important warnings:

• If you’re taking anticoagulant medications, consult your healthcare provider before taking vitamin K supplements, as they can interfere with medication effectiveness
• Very high doses of synthetic K2 (MK-4) have been used in some studies (45 mg daily) without apparent harm, but long-term safety data is limited
• MK-7 supplements in doses of 90-360 mcg daily have been used safely in research studies
• More is not always better—aim for physiological doses that mimic what you might get from a nutrient-rich diet

Before starting any supplement regimen, discuss it with a qualified healthcare provider who can evaluate your individual needs and health status.

The Synergistic Relationship with Other Nutrients

Vitamin K and Vitamin D

Vitamins K and D work together in calcium metabolism. Vitamin D increases the production of vitamin K-dependent proteins like osteocalcin and MGP, but these proteins require vitamin K to become activated. Some experts believe that widespread vitamin D supplementation without adequate K2 intake might contribute to arterial calcification by increasing calcium absorption without proper regulatory proteins.

If you’re taking high-dose vitamin D supplements, ensuring adequate K2 intake may be particularly important.

Vitamin K and Calcium

Vitamin K doesn’t work to improve bone health in isolation—adequate calcium intake is also essential. Think of calcium as the building material and vitamin K as the construction foreman directing where it should go. Without sufficient calcium, vitamin K has nothing to work with; without vitamin K, calcium may end up in the wrong places.

Vitamin K and Magnesium

Magnesium is required for the conversion of vitamin K into its active form. Magnesium deficiency might therefore impair vitamin K function, even when K intake is adequate.

Special Considerations for Different Life Stages

Infancy and Childhood

Newborns have low vitamin K stores and limited intestinal bacteria for K2 production. This is why vitamin K injections are routinely given to newborns in many countries to prevent vitamin K deficiency bleeding. As children grow, ensuring adequate intake through diet becomes important for supporting growth and bone development.

Pregnancy and Lactation

Vitamin K is essential during pregnancy for proper fetal development and blood clotting. Breast milk is relatively low in vitamin K compared to infant needs, which is another reason for supplementation at birth. Pregnant and lactating women should ensure adequate intake through diet or supplementation as recommended by their healthcare provider.

Older Adults

As we age, several factors may affect vitamin K status:

• Reduced food intake may limit vitamin K consumption
• Changes in gut bacteria may affect K2 production
• Medications may interfere with vitamin K function
• Malabsorption may become more common

Older adults may benefit particularly from ensuring adequate K2 intake for bone and cardiovascular health.

Frequently Asked Questions

Can you get too much vitamin K from food?

No, there’s no known toxicity from vitamin K consumed through food. Your body has mechanisms to regulate absorption and excretion. However, sudden large increases in vitamin K-rich foods can affect blood-thinning medication, so consistency is key if you’re on such medications.

Is one form superior to the other?

Both forms have important functions. K1 is particularly important for blood clotting and is easier to obtain from diet. K2 may be more effective for bone and cardiovascular health due to its better distribution throughout the body. The ideal approach is consuming adequate amounts of both forms.

Do gut bacteria produce enough K2?

While gut bacteria do produce vitamin K2, most of this production occurs in the colon, where absorption is limited. You cannot rely on bacterial production alone and should include dietary sources of K2.

Does cooking destroy vitamin K?

Vitamin K is relatively heat-stable, so normal cooking doesn’t significantly reduce its content. In fact, lightly cooking some vegetables may improve K1 bioavailability by breaking down plant cell walls, making the vitamin more accessible.

Can vitamin K2 remove existing arterial plaque?

While some studies suggest K2 may slow or stop the progression of arterial calcification, there’s limited evidence that it can reverse existing plaque. Prevention appears to be more effective than reversal.

Conclusion: A Balanced Approach to Vitamin K Nutrition

Understanding the differences between vitamin K1 and K2 highlights the importance of consuming a varied, nutrient-dense diet. While both forms share some overlapping functions, they each offer unique benefits that support different aspects of health.

Vitamin K1, abundant in leafy green vegetables, is essential for proper blood clotting and readily available in plant-based foods. Getting adequate K1 is relatively straightforward—just include a serving of greens in your daily diet.

Vitamin K2, found in fermented foods and animal products, appears particularly important for bone and cardiovascular health due to its superior absorption and distribution throughout the body. While K2 can be more challenging to obtain in Western diets, incorporating fermented foods, grass-fed animal products, and certain cheeses can help ensure adequate intake.

Rather than focusing on one form over the other, the best approach is to include diverse sources of both vitamin K1 and K2 in your regular diet. Eat your leafy greens, enjoy fermented foods like cheese and sauerkraut, choose grass-fed animal products when possible, and consider trying natto if you’re adventurous.

For most healthy individuals eating a varied diet, supplementation isn’t necessary. However, if you have specific health concerns, follow a restrictive diet, or take medications that affect vitamin K, discuss your needs with a healthcare provider who can provide personalized recommendations.

By understanding and optimizing your intake of both forms of vitamin K, you can support healthy blood clotting, maintain strong bones, protect your cardiovascular system, and potentially reduce your risk of chronic diseases as you age.

Sources:

• National Institutes of Health – Vitamin K Research
• Office of Dietary Supplements – Vitamin K Fact Sheet
• PubMed – Vitamin K1 and K2 Metabolism
• USDA FoodData Central – Vitamin K Content Database
• PubMed – Vitamin K2 and Cardiovascular Health
• PubMed – Vitamin K and Bone Health Studies
• Mayo Clinic – Vitamin K Overview