Vitamin K2: Complete Guide to Benefits, Sources, and Dosage

Vitamin K2 is an essential nutrient that plays a critical role in numerous bodily functions, from supporting cardiovascular health to maintaining strong bones and teeth. Despite its importance, vitamin K2 remains one of the most underappreciated and misunderstood vitamins in modern nutrition.

First identified in the late 1920s for its role in blood coagulation, vitamin K has since been recognized for its far-reaching effects on overall health. While many people are familiar with vitamin K1, vitamin K2 is gaining attention for its unique and powerful health benefits.

This comprehensive guide explores what vitamin K2 is, how it differs from other forms of vitamin K, its evidence-based health benefits, and practical ways to ensure you’re getting enough of this vital nutrient.

What Is Vitamin K2?

Vitamin K is a family of fat-soluble vitamins that share similar chemical structures but have distinct functions in the body. The vitamin K family is divided into two main groups:

• Vitamin K1 (Phylloquinone): Primarily found in green leafy vegetables and plant-based foods. It accounts for approximately 75-90% of vitamin K intake in typical Western diets.
• Vitamin K2 (Menaquinone): Found predominantly in animal products, fermented foods, and also synthesized by bacteria in the human gut.

Vitamin K2 can be further categorized into several subtypes based on the length of their side chains, ranging from MK-4 to MK-13. The most significant and well-studied forms are:

• MK-4: Found in animal-based foods such as meat, eggs, and dairy products. It has a shorter half-life in the body.
• MK-7: Present in fermented foods, particularly natto (fermented soybeans). It has a longer half-life and remains bioavailable in the body for extended periods.

While vitamin K1 is primarily involved in blood clotting, vitamin K2 serves broader functions, particularly in directing calcium to appropriate locations in the body—namely, bones and teeth rather than soft tissues and arteries.

How Does Vitamin K2 Work in the Body?

Vitamin K2 functions as a cofactor for enzymes that activate specific proteins through a process called carboxylation. The two most important proteins activated by vitamin K2 are:

Matrix Gla Protein (MGP)

Matrix Gla protein is a powerful inhibitor of vascular calcification. When activated by vitamin K2, MGP prevents calcium from depositing in blood vessel walls, thereby protecting against arterial stiffness and cardiovascular disease. Without adequate vitamin K2, MGP remains inactive and cannot perform this protective function.

Osteocalcin

Osteocalcin is produced by bone-building cells called osteoblasts. When activated by vitamin K2, osteocalcin binds calcium and directs it into bone tissue, promoting bone mineralization and strength. This protein is essential for maintaining healthy bone density and reducing fracture risk.

Through these mechanisms, vitamin K2 essentially acts as a calcium traffic controller, ensuring this important mineral ends up where it’s beneficial (bones and teeth) rather than where it can cause harm (arteries and soft tissues).

Vitamin K2 and Heart Health

Cardiovascular disease remains the leading cause of death worldwide, and arterial calcification is a major contributing factor. When calcium accumulates in arterial walls, blood vessels become rigid and less elastic, increasing blood pressure and the risk of heart attack and stroke.

Research suggests that vitamin K2 may play a protective role against cardiovascular disease through its activation of matrix Gla protein. Several large-scale observational studies have examined the relationship between vitamin K2 intake and heart health outcomes.

The Rotterdam Study, one of the most comprehensive investigations into vitamin K2 and cardiovascular health, followed over 4,800 participants for seven years. Researchers found that those with the highest intake of vitamin K2 had a significantly reduced risk of coronary heart disease and arterial calcification compared to those with the lowest intake.

A comprehensive meta-analysis examining data from more than 200,000 participants across multiple studies found that increased dietary intake of vitamin K was associated with a moderately reduced risk of coronary heart disease. Notably, vitamin K2 appeared to have a more pronounced protective effect than vitamin K1.

While these findings are promising, it’s important to note that most evidence comes from observational studies, which can identify associations but cannot prove causation. More long-term randomized controlled trials are needed to definitively establish vitamin K2’s role in preventing heart disease.

Vitamin K2 for Bone Health and Osteoporosis Prevention

Osteoporosis affects millions of people worldwide, particularly postmenopausal women and older adults. This condition is characterized by reduced bone mineral density and increased fracture risk, leading to significant morbidity and reduced quality of life.

Vitamin K2’s role in activating osteocalcin makes it crucial for bone health. When osteocalcin is properly activated, it enhances calcium incorporation into the bone matrix, promoting bone strength and density.

Several clinical studies have investigated vitamin K2 supplementation for bone health with encouraging results. Research involving postmenopausal women has shown that vitamin K2 supplementation can help maintain bone mineral density and reduce fracture incidence.

A meta-analysis examining 16 studies with over 6,400 postmenopausal women found that vitamin K2 supplementation had positive effects on bone mineralization and increased bone strength. The studies used various doses and forms of vitamin K2, with MK-4 and MK-7 being the most commonly studied.

Japanese research has been particularly extensive in this area, with multiple studies demonstrating that vitamin K2 supplementation can reduce vertebral fractures in individuals with osteoporosis. Japan has even approved pharmaceutical-grade vitamin K2 (as MK-4) for the treatment of osteoporosis.

However, research findings have not been entirely consistent across all populations and study designs. Some recent trials have shown mixed results, highlighting the need for additional high-quality, long-term studies to establish optimal dosing recommendations and identify which populations benefit most from vitamin K2 supplementation.

Vitamin K2 and Dental Health

The same mechanisms that make vitamin K2 important for bone health also apply to dental health. Teeth, like bones, require proper calcium metabolism for strength and maintenance.

Osteocalcin, the vitamin K2-dependent protein crucial for bone health, is also one of the main proteins involved in dental health. It triggers mechanisms that promote the growth of dentin, the calcified tissue that forms the bulk of tooth structure beneath the enamel.

Historical and anthropological evidence suggests that vitamin K2 may have played a significant role in dental health before the modern era. Dr. Weston A. Price, a dentist who studied traditional diets in the early 20th century, observed that populations consuming traditional diets rich in what he called “Activator X” (now believed to be vitamin K2) had excellent dental health with minimal cavities.

Recent research has begun to support these observations. Studies examining the relationship between vitamin K intake and periodontal disease have found that adequate vitamin K consumption, particularly when combined with sufficient fiber intake, may help prevent tooth loss from periodontal disease.

Vitamins A and D appear to work synergistically with vitamin K2 in supporting dental health, suggesting that a comprehensive approach to nutrition is important for maintaining healthy teeth and gums.

Potential Role in Cancer Prevention

Emerging research has explored potential connections between vitamin K2 and cancer prevention, though this area of study is still in early stages.

Cell culture and animal studies have suggested that vitamin K2 may inhibit the growth and proliferation of certain cancer cell types, particularly liver cancer cells. Some research has indicated that vitamin K2 might support reduced recurrence rates in individuals with liver cancer, though larger, well-controlled human trials are needed to confirm these findings.

Studies examining vitamin K2 and other cancer types have produced mixed results. Some research has found associations between higher vitamin K2 intake and reduced risk of certain cancers, while other studies have found neutral or even contradictory results.

Given the preliminary nature of this research, it would be premature to recommend vitamin K2 specifically for cancer prevention. However, ensuring adequate vitamin K2 intake as part of an overall healthy diet may contribute to general health and disease prevention.

Food Sources of Vitamin K2

Unlike vitamin K1, which is abundant in leafy green vegetables and widely available in typical diets, vitamin K2 is less common and found primarily in specific animal and fermented foods.

Animal-Based Sources

Animal products contain the MK-4 form of vitamin K2. The richest sources include:

• Grass-fed dairy products: Full-fat cheese, butter, and cream from grass-fed animals contain significantly more vitamin K2 than products from grain-fed animals. Hard cheeses like Gouda and Brie are particularly rich sources.
• Egg yolks: Eggs from pasture-raised chickens contain higher levels of vitamin K2 than conventional eggs.
• Organ meats: Liver and other organ meats provide substantial amounts of vitamin K2.
• Dark meat poultry: Chicken thighs and legs contain more vitamin K2 than white meat.

It’s important to note that vitamin K2 is fat-soluble, so low-fat or fat-free dairy products contain minimal amounts of this nutrient. Choosing full-fat versions from grass-fed or pasture-raised animals provides the most vitamin K2.

Fermented Foods

Fermented foods contain longer-chain forms of vitamin K2, particularly MK-7, which has superior bioavailability and longer retention in the body. Notable sources include:

• Natto: This traditional Japanese food made from fermented soybeans is by far the richest known source of vitamin K2, containing extraordinary amounts of MK-7. Just one serving can provide several days’ worth of vitamin K2.
• Sauerkraut: Fermented cabbage contains moderate amounts of vitamin K2, though much less than natto.
• Miso: Fermented soybean paste used in Japanese cuisine provides some vitamin K2.
• Certain cheeses: Some aged and fermented cheeses contain both MK-4 (from the animal fat) and MK-7 (from bacterial fermentation).

Gut Bacteria Production

Bacteria in the human large intestine can synthesize vitamin K2. The extent to which this internally produced vitamin K2 contributes to overall vitamin K status is not fully understood, though it’s believed to provide some benefit.

Factors that may affect gut bacteria’s ability to produce vitamin K2 include diet quality, antibiotic use, and overall gut health. Maintaining a healthy gut microbiome through a diverse, fiber-rich diet and judicious use of antibiotics may support optimal vitamin K2 production.

Vitamin K2 Deficiency

Unlike some other nutrients, overt vitamin K2 deficiency is relatively uncommon in healthy populations. However, suboptimal levels may be more widespread than previously thought, particularly in individuals consuming typical Western diets low in fermented foods and high-quality animal products.

Risk Factors for Low Vitamin K2 Status

• Limited dietary intake: Diets low in full-fat dairy, organ meats, and fermented foods
• Fat malabsorption disorders: Conditions affecting fat absorption, such as celiac disease, Crohn’s disease, or chronic pancreatitis
• Long-term antibiotic use: May disrupt gut bacteria that produce vitamin K2
• Certain medications: Some drugs may interfere with vitamin K metabolism
• Low-fat diets: Since vitamin K2 is fat-soluble, very low-fat diets may limit absorption

Signs of Inadequate Vitamin K Status

Because vitamin K2 deficiency develops gradually and its effects are internal, symptoms are often subtle or absent until significant problems develop. Potential indicators of insufficient vitamin K2 include:

• Easy bruising or excessive bleeding
• Reduced bone mineral density
• Increased arterial calcification (detected through medical imaging)
• Elevated levels of undercarboxylated (inactive) osteocalcin or MGP in blood tests

Vitamin K2 Supplementation

For individuals who have difficulty obtaining adequate vitamin K2 from diet alone, supplementation may be beneficial. Vitamin K2 supplements are available in several forms:

Types of Vitamin K2 Supplements

• MK-4: Typically requires higher doses and more frequent administration due to its shorter half-life. Often derived synthetically.
• MK-7: Offers better bioavailability and longer duration of action, allowing for once-daily dosing at lower amounts. Usually derived from natto or produced through bacterial fermentation.

Dosage Considerations

There is no established Recommended Dietary Allowance (RDA) for vitamin K2 specifically, as most official recommendations combine K1 and K2. Common supplementation doses range from:

• MK-7: 90-200 micrograms (mcg) daily for general health support
• MK-4: 45 milligrams (mg) daily in therapeutic applications, though this high dose is typically used in clinical settings

Before starting any supplementation regimen, it’s advisable to consult with a healthcare professional, especially if you have existing health conditions or take medications.

Combining Vitamin K2 with Other Nutrients

Vitamin K2 works synergistically with several other nutrients, particularly:

• Vitamin D: These two vitamins work together in calcium metabolism. Vitamin D promotes calcium absorption, while vitamin K2 directs where that calcium goes. Many experts recommend taking them together.
• Vitamin A: Supports vitamin K2’s functions and may enhance its effectiveness.
• Calcium: While vitamin K2 helps direct calcium, adequate calcium intake is still necessary for bone health.
• Magnesium: Required for vitamin D activation and works alongside calcium and vitamin K2 in bone metabolism.

Safety and Side Effects

Vitamin K2 has an excellent safety profile with minimal risk of toxicity. No tolerable upper intake level has been established because adverse effects from high intake have not been identified in healthy populations.

Unlike some fat-soluble vitamins (such as vitamins A and D), vitamin K does not accumulate to toxic levels in the body. Research has shown that even very high doses of vitamin K2 are well-tolerated without significant adverse effects.

Important Considerations

While vitamin K2 is generally safe, there are some situations requiring caution:

• Blood-thinning medications: Individuals taking anticoagulant medications, particularly warfarin (Coumadin), need to maintain consistent vitamin K intake and should consult their healthcare provider before changing vitamin K consumption or starting supplements. Sudden increases or fluctuations in vitamin K intake can interfere with these medications’ effectiveness.
• Pregnancy and breastfeeding: While vitamin K2 appears safe during pregnancy and lactation, pregnant or nursing women should consult healthcare providers before taking supplements.
• Upcoming surgery: Some healthcare providers recommend temporarily discontinuing vitamin K supplements before surgical procedures, though this is typically more relevant for higher doses.

Vitamin K1 vs. Vitamin K2: Understanding the Differences

While both forms of vitamin K share some structural similarities and can perform overlapping functions, they have distinct characteristics:

Vitamin K1 (Phylloquinone)

• Primary role in blood clotting
• Abundant in green leafy vegetables
• Shorter retention time in the body
• Preferentially taken up by the liver
• Less efficiently absorbed (only 10-15% bioavailability)

Vitamin K2 (Menaquinone)

• Primary roles in bone and cardiovascular health
• Found in animal products and fermented foods
• Longer retention, especially MK-7
• Better distribution to extrahepatic tissues (bones, blood vessels)
• Better bioavailability, particularly MK-7

The body can convert some vitamin K1 to K2, but this conversion process is inefficient. Most K1 is rapidly metabolized and excreted, while K2 remains in circulation longer and reaches more tissues.

How Much Vitamin K2 Do You Need?

Determining optimal vitamin K2 intake is challenging because official nutritional guidelines typically don’t distinguish between K1 and K2, instead providing recommendations for total vitamin K.

The current Adequate Intake (AI) for total vitamin K in adults is:

• Men: 120 micrograms daily
• Women: 90 micrograms daily

However, these recommendations were established primarily based on vitamin K’s role in blood clotting and may not reflect optimal amounts for bone and cardiovascular health.

Some researchers suggest that the vitamin K2 intake specifically needed for optimal activation of osteocalcin and matrix Gla protein may be higher than what typical diets provide. Observational studies showing cardiovascular benefits have found positive effects with vitamin K2 intakes ranging from 30 to 45 micrograms daily.

Testing Vitamin K Status

Unlike many vitamins, there is no standard, widely available blood test to directly measure vitamin K2 levels. However, several markers can indicate vitamin K status:

• Undercarboxylated osteocalcin: Higher levels indicate insufficient vitamin K2 for proper osteocalcin activation
• Undercarboxylated MGP: Elevated levels suggest inadequate vitamin K2 for cardiovascular protection
• Prothrombin time: While primarily used to monitor blood clotting, prolonged prothrombin time can indicate severe vitamin K deficiency

These specialized tests are not routinely performed but may be useful in specific clinical situations or research settings.

Practical Tips for Increasing Vitamin K2 Intake

If you want to optimize your vitamin K2 status through dietary changes, consider these strategies:

Dietary Approaches

• Choose full-fat dairy: Opt for full-fat cheese, butter, and yogurt from grass-fed sources when possible
• Include egg yolks: Don’t skip the yolks; choose eggs from pasture-raised chickens for higher nutrient content
• Try fermented foods: Incorporate sauerkraut, certain cheeses, or natto (if you can acquire the taste) into your diet
• Select quality animal products: When consuming meat and poultry, choose products from animals raised on pasture
• Consider organ meats: Liver and other organ meats are nutrient-dense sources of vitamin K2
• Use vitamin K2-rich fats: Cook with butter from grass-fed cows or ghee

Maximizing Absorption

Since vitamin K2 is fat-soluble, consuming it with dietary fat enhances absorption. When eating vitamin K2-rich foods or taking supplements, include them as part of a meal containing healthy fats for optimal uptake.

Special Populations and Vitamin K2

Older Adults

Aging is associated with increased risk of both osteoporosis and cardiovascular disease—two conditions where vitamin K2 may be particularly beneficial. Older adults may benefit from ensuring adequate vitamin K2 intake through diet or supplementation, though individual needs should be discussed with healthcare providers.

Postmenopausal Women

The hormonal changes of menopause accelerate bone loss, increasing osteoporosis risk. Research suggests vitamin K2 supplementation may help maintain bone density in this population, making adequate intake particularly important.

People with Digestive Disorders

Conditions affecting fat absorption, such as celiac disease, inflammatory bowel disease, or those who have had bariatric surgery, may have difficulty absorbing fat-soluble vitamins including vitamin K2. These individuals may require higher intake or supplementation under medical supervision.

Vegans and Vegetarians

Since vitamin K2 is found primarily in animal products, those following plant-based diets may have lower intake. Natto is an excellent plant-based source of vitamin K2 (MK-7), though its strong flavor can be challenging for some. Fermented vegetables and some plant-based supplements may also help meet needs.

The Future of Vitamin K2 Research

While substantial evidence supports vitamin K2’s importance for health, many questions remain. Ongoing and future research is exploring:

• Optimal dosing strategies for different health outcomes
• Long-term effects of supplementation on cardiovascular disease and fracture prevention
• Potential benefits for other conditions, including cognitive function and metabolic health
• Individual variations in vitamin K2 needs based on genetics and other factors
• The role of gut microbiome in vitamin K2 production and status

As research advances, our understanding of this important nutrient and its applications in preventive health will continue to evolve.

Frequently Asked Questions About Vitamin K2

Can you get too much vitamin K2?

Vitamin K2 toxicity has not been observed even at high supplemental doses. No upper limit has been established because excessive intake has not been shown to cause adverse effects in healthy individuals. However, those on blood-thinning medications should consult their healthcare provider before supplementing.

Is vitamin K2 better than vitamin K1?

Rather than one being “better,” these two forms of vitamin K serve different primary functions in the body. Vitamin K1 is essential for blood clotting, while vitamin K2 plays unique roles in bone and cardiovascular health. Both are important, and an optimal diet includes adequate amounts of both forms.

How long does it take for vitamin K2 to work?

The timeframe depends on what outcome you’re measuring. Vitamin K2 begins activating proteins within hours to days of consumption, but measurable changes in bone density or cardiovascular markers may take months to years of consistent adequate intake.

Should I take vitamin K2 if I’m already taking vitamin D?

Many experts recommend taking vitamin K2 alongside vitamin D supplementation because these nutrients work synergistically in calcium metabolism. Vitamin D increases calcium absorption, while vitamin K2 helps direct that calcium to appropriate locations. However, discuss supplement combinations with a healthcare provider.

What’s the best time of day to take vitamin K2?

Since vitamin K2 is fat-soluble, it’s best absorbed when taken with a meal containing fats. The specific time of day is less important than consistency and taking it with appropriate foods or dietary fat.

Does cooking destroy vitamin K2?

Vitamin K2 is relatively stable during cooking and food preparation. Unlike some vitamins that are heat-sensitive, vitamin K2 withstands typical cooking temperatures reasonably well, though extended high-heat exposure may reduce content somewhat.

Conclusion

Vitamin K2 is an essential nutrient that deserves greater recognition for its vital roles in health maintenance and disease prevention. From directing calcium to build strong bones to preventing arterial calcification that contributes to heart disease, vitamin K2 performs functions that few other nutrients can replicate.

While more research will continue to refine our understanding of optimal intake levels and therapeutic applications, current evidence strongly supports ensuring adequate vitamin K2 consumption as part of a comprehensive approach to health.

Whether through incorporating K2-rich foods like full-fat dairy products from grass-fed animals, fermented foods, or appropriate supplementation, paying attention to this often-overlooked nutrient may offer significant long-term health benefits.

For most people, combining a diet rich in both vitamin K1 (from leafy greens) and vitamin K2 (from quality animal products and fermented foods) provides the foundation for optimal vitamin K status. Those with specific health concerns, dietary restrictions, or medical conditions should consult with qualified healthcare professionals to determine their individual vitamin K2 needs.

By understanding vitamin K2’s importance and taking steps to ensure adequate intake, you can support your body’s natural processes for maintaining strong bones, healthy blood vessels, and overall wellness throughout life.

Sources:

• National Institutes of Health – Vitamin K Metabolism
• PubMed Central – Arterial Calcification and Cardiovascular Risk
• PubMed – Vitamin K and Calcium Metabolism
• PubMed – Vitamin K Intake and Coronary Heart Disease Meta-Analysis
• BMJ Open Heart – Dietary Vitamin K and Heart Disease
• PubMed – Vitamin K2 and Bone Mineralization Meta-Analysis
• PubMed Central – Osteocalcin and Dental Health
• PubMed Central – Vitamin K2 and Bone Formation
• PubMed – Vitamin K2 and Cancer Cell Growth
• PubMed Central – Dietary Sources of Vitamin K2
• PubMed Central – Vitamin K2 and D Synergistic Effects
• Frontiers in Immunology – Gut Bacteria and Vitamin K2
• PubMed Central – Vitamin K and Anticoagulant Interactions