Vitamin K is a fat-soluble vitamin crucial for various bodily functions, encompassing compounds like phylloquinone (vitamin K1) and menaquinones (vitamin K2). While vitamin K1 is abundant in leafy greens, vitamin K2, particularly menaquinones, is found in animal products and fermented foods, making “Vitamin K2 Foods” a key area of interest for dietary health. This article delves into the world of vitamin K2 foods, exploring their importance, sources, and health benefits, providing an in-depth guide for incorporating them into a balanced diet.
Understanding Vitamin K2: Menaquinones and Their Role
Vitamin K2, or menaquinone, isn’t a single compound but a group of vitamers, most notably MK-4 through MK-13, differentiated by their isoprenyl side chains. Among these, MK-4, MK-7, and MK-9 are the most researched. While phylloquinone (K1) is the primary dietary form from plants, menaquinones are largely produced by bacteria and are present in specific food categories. Notably, our gut bacteria also produce menaquinones, especially the longer-chain forms, contributing to our overall vitamin K status. Interestingly, MK-4 is unique as it can be synthesized in the body from vitamin K1, independent of bacterial action.
Vitamin K, whether K1 or K2, acts as a vital coenzyme for vitamin K-dependent carboxylase. This enzyme is essential for synthesizing proteins involved in crucial processes like hemostasis (blood clotting), bone metabolism, and other physiological functions. Prothrombin, a key protein in blood clotting, is vitamin K-dependent. It’s also important to note the interaction with anticoagulants like warfarin, which work by antagonizing vitamin K’s action, highlighting the need for consistent vitamin K intake for individuals on these medications.
Beyond blood clotting, vitamin K2 plays a significant role in calcium regulation and bone health. Matrix Gla-protein (MGP), a vitamin K-dependent protein found in blood vessels and bones, is believed to help prevent abnormal calcium buildup in arteries, potentially supporting cardiovascular health. Osteocalcin, another vitamin K-dependent protein in bone, is involved in bone mineralization and turnover. These functions underscore the importance of adequate vitamin K2 intake for both skeletal and cardiovascular well-being.
Like other fat-soluble vitamins, vitamin K2 from foods is absorbed in the small intestine with the help of bile and pancreatic enzymes. It’s then transported to the liver and distributed throughout the body, including vital organs and bone tissue. However, vitamin K is metabolized and excreted relatively quickly compared to other fat-soluble vitamins, emphasizing the need for regular intake through vitamin k2 foods and other sources.
While the exact absorption and utilization of vitamin K2 produced by gut bacteria are still being researched, it’s understood that these menaquinones, particularly long-chain forms, are present in the colon in substantial amounts. Experts believe this bacterial production contributes to meeting our vitamin K requirements, alongside dietary sources of vitamin k2 foods.
Top Vitamin K2 Foods to Include in Your Diet
When focusing on “vitamin k2 foods,” certain categories stand out as excellent sources. It’s important to note that food composition data often primarily lists phylloquinone (K1) content, and information on menaquinone content is still evolving. However, we can identify key vitamin k2 foods based on current research.
Natto: The King of Vitamin K2 Foods
Natto, a traditional Japanese dish made from fermented soybeans, is arguably the richest food source of vitamin K2, specifically MK-7. The fermentation process by Bacillus subtilis natto bacteria is responsible for the high MK-7 content. Just 3 ounces of natto can provide upwards of 850 mcg of vitamin K2, far exceeding daily recommended intakes. While its strong flavor and sticky texture might be an acquired taste, natto’s exceptional vitamin K2 concentration makes it a nutritional powerhouse among vitamin k2 foods.
Fermented Cheeses: A Palatable Source of Menaquinones
Certain fermented cheeses are significant contributors to dietary vitamin K2. The types and amounts of menaquinones in cheese vary depending on the specific bacterial strains used during fermentation and the fermentation conditions. Hard cheeses, particularly aged varieties, tend to contain higher levels of MK-9 and MK-8, produced by bacteria involved in their ripening. Examples include Gouda, Edam, and cheddar. While cheese contains less vitamin K2 than natto, it is a more widely consumed and palatable vitamin k2 food source for many.
Animal Products: Meat, Poultry, and Eggs
Animal products, especially certain cuts of meat, poultry, and eggs, provide vitamin K2, primarily as MK-4. Animals can convert phylloquinone (K1) from their plant-based diet into MK-4. Organ meats like liver are particularly rich in MK-4. Chicken, especially dark meat, and pork also contain notable amounts. Egg yolks are another source of MK-4. The vitamin K2 content in animal products can be influenced by the animal’s diet, particularly if their feed is supplemented with menadione, a synthetic form of vitamin K, which can be converted to MK-4 in animal tissues. Therefore, choosing pasture-raised or grass-fed animal products might offer a more natural and potentially higher vitamin K2 content.
Other Fermented Foods: Sauerkraut and Kimchi
Beyond natto and cheese, other fermented foods like sauerkraut and kimchi can contribute to vitamin K2 intake. The bacterial fermentation process in these foods can produce menaquinones. However, the specific types and amounts of vitamin K2 can vary depending on the fermentation methods and bacterial cultures involved. While not as concentrated as natto, incorporating a variety of fermented foods, including sauerkraut and kimchi, can diversify your intake of vitamin k2 foods.
It’s important to note that while vegetables like leafy greens are excellent sources of vitamin K1, they are not significant sources of vitamin K2. To specifically increase your vitamin K2 intake, focusing on the food categories listed above – natto, fermented cheeses, animal products, and other fermented foods – is most effective.
Health Benefits of Vitamin K2 Rich Foods
Consuming vitamin k2 foods offers a range of potential health benefits, largely attributed to vitamin K2’s unique roles in the body beyond blood clotting.
Bone Health and Osteoporosis Prevention
Vitamin K2 is increasingly recognized for its crucial role in bone health. It activates osteocalcin, a protein that helps bind calcium to bone, promoting bone mineralization and strength. Research suggests that vitamin K2 may be more effective than vitamin K1 in supporting bone health. Studies, particularly those using MK-4 and MK-7 forms of vitamin K2, have shown promising results in improving bone mineral density and reducing fracture risk, especially in postmenopausal women who are at higher risk of osteoporosis. Including vitamin k2 foods in the diet can be a proactive step towards maintaining strong and healthy bones throughout life.
Cardiovascular Health and Reduced Calcification
Vitamin K2’s potential benefits extend to cardiovascular health, primarily through its activation of Matrix Gla-protein (MGP). MGP is believed to inhibit calcium deposits in arteries, preventing arterial calcification, a significant risk factor for heart disease. Observational studies have linked higher intakes of menaquinones, particularly from vitamin k2 foods, with a reduced risk of coronary heart disease and aortic calcification. While more research is needed, especially through clinical trials, the evidence suggests that vitamin k2 foods may contribute to cardiovascular protection by supporting healthy arteries and reducing calcification.
Other Potential Health Benefits
Emerging research suggests vitamin K2 may have other health benefits, including potential roles in:
- Dental Health: By activating osteocalcin in dentin, vitamin K2 may contribute to stronger teeth.
- Cancer Prevention: Some studies suggest vitamin K2 may have anti-cancer properties, although more research is needed.
- Improved Insulin Sensitivity: Preliminary studies indicate vitamin K2 might play a role in glucose metabolism and insulin sensitivity.
While these areas are still under investigation, the existing evidence highlights the diverse potential health benefits of incorporating vitamin k2 foods into your diet beyond the well-established roles in blood clotting and bone health.
Recommended Intake of Vitamin K and Vitamin K2
Dietary Reference Intakes (DRIs) for vitamin K are established by the Food and Nutrition Board (FNB). Currently, Adequate Intakes (AIs) are set for vitamin K, as there’s insufficient data to establish an Estimated Average Requirement (EAR). The AI values are based on vitamin K intakes in healthy populations and are intended to ensure nutritional adequacy.
Adequate Intakes (AIs) for Vitamin K (mcg):
| Age Group | Male | Female | Pregnancy | Lactation |
|---|---|---|---|---|
| Birth to 6 months | 2.0 | 2.0 | ||
| 7–12 months | 2.5 | 2.5 | ||
| 1–3 years | 30 | 30 | ||
| 4–8 years | 55 | 55 | ||
| 9–13 years | 60 | 60 | ||
| 14–18 years | 75 | 75 | 75 | 75 |
| 19+ years | 120 | 90 | 90 | 90 |
These AIs are for total vitamin K intake (K1 and K2 combined). Currently, there are no specific RDAs or AIs specifically for vitamin K2. However, given the emerging research highlighting the distinct benefits of vitamin K2, particularly menaquinones, many experts suggest ensuring adequate intake of vitamin k2 foods as part of a balanced diet. For adults, aiming for at least the general AI for vitamin K, while prioritizing vitamin k2 foods like natto, fermented cheeses, and animal products, can be a practical approach.
It’s worth noting that vitamin K deficiency is rare in healthy adults due to the widespread availability of vitamin K in foods and the body’s ability to produce some vitamin K2 in the gut. However, certain groups may be at higher risk, emphasizing the importance of adequate vitamin K intake, including vitamin k2 foods.
Vitamin K Deficiency and At-Risk Groups
While overt vitamin K deficiency is uncommon in healthy adults, inadequate vitamin K status can still have health implications. Clinical vitamin K deficiency is primarily identified by prolonged prothrombin time, indicating impaired blood clotting. Severe deficiency can lead to bleeding and hemorrhage. Subclinical vitamin K inadequacy, which may be more prevalent, could potentially impact bone health and other vitamin K-dependent processes over time.
Groups at higher risk of vitamin K inadequacy include:
- Newborns: Vitamin K transfer across the placenta is limited, and breast milk is relatively low in vitamin K. Newborns are routinely given vitamin K injections at birth to prevent Vitamin K Deficiency Bleeding (VKDB).
- Individuals with Malabsorption Disorders: Conditions like cystic fibrosis, celiac disease, and inflammatory bowel diseases can impair vitamin K absorption.
- People Taking Certain Medications: Warfarin, antibiotics, bile acid sequestrants, and orlistat can interfere with vitamin K metabolism or absorption.
For these at-risk groups, ensuring adequate vitamin K intake, potentially including vitamin k2 supplements under medical guidance, is particularly important. However, for the general population, focusing on a diet rich in vitamin k foods and vitamin K1 sources like leafy greens is usually sufficient to maintain adequate vitamin K status.
Vitamin K Interactions and Precautions
Vitamin K can interact with certain medications, and vice versa. It’s crucial to be aware of these interactions, especially if you are taking medications regularly.
Warfarin and Similar Anticoagulants
Vitamin K can significantly interact with anticoagulants like warfarin (Coumadin). These drugs work by inhibiting vitamin K’s action in blood clotting. Therefore, individuals taking warfarin need to maintain a consistent vitamin K intake from diet and supplements to ensure stable anticoagulation. Sudden changes in vitamin K intake, whether increases or decreases, can affect the drug’s effectiveness and potentially lead to bleeding or clotting complications. It’s essential for individuals on warfarin to discuss their vitamin K intake with their healthcare provider.
Antibiotics
Certain antibiotics, particularly cephalosporins, can disrupt vitamin K metabolism in two ways: by killing vitamin K-producing bacteria in the gut and by potentially inhibiting vitamin K’s action in the body. Prolonged antibiotic use, especially with poor dietary vitamin K intake, could increase the risk of vitamin K deficiency. However, vitamin K supplementation is usually not necessary unless antibiotic use is long-term (several weeks) and dietary intake is inadequate.
Bile Acid Sequestrants and Orlistat
Bile acid sequestrants (like cholestyramine and colestipol), used to lower cholesterol, and orlistat (a weight-loss drug) can reduce the absorption of fat-soluble vitamins, including vitamin K. While the clinical significance of this effect is not always clear, long-term use of these medications may warrant monitoring vitamin K status, especially for bile acid sequestrants. For orlistat, clinicians often recommend multivitamin supplementation containing vitamin K.
If you are taking any of these medications or other prescription drugs, it’s advisable to discuss your vitamin K intake and status with your healthcare provider to ensure safe and effective medication management.
Incorporating Vitamin K2 Foods into Your Diet
Making vitamin k2 foods a regular part of your diet can be both beneficial and enjoyable. Here are some practical tips:
- Embrace Natto: If you can acquire the taste, natto is a vitamin K2 powerhouse. Start with small portions and try different preparations.
- Enjoy Fermented Cheeses: Include aged cheeses like Gouda, Edam, or cheddar in moderation as part of a balanced diet.
- Choose Quality Animal Products: Opt for pasture-raised or grass-fed meat, poultry, and eggs when possible, and include organ meats like liver occasionally.
- Explore Other Fermented Foods: Experiment with sauerkraut, kimchi, and other fermented vegetables to diversify your vitamin K2 intake and support gut health.
- Combine with Healthy Fats: Since vitamin K is fat-soluble, consuming vitamin k2 foods with healthy fats can enhance absorption.
Remember, a balanced dietary pattern that includes a variety of nutrient-rich foods, including vitamin k2 foods, is key for overall health and well-being.
Conclusion: Embrace Vitamin K2 Foods for Optimal Health
Vitamin K2, particularly menaquinones found in vitamin k2 foods, plays a vital role in bone health, cardiovascular health, and potentially other aspects of well-being. While vitamin K deficiency is rare in healthy adults, ensuring adequate intake of vitamin K, including vitamin K2 from food sources like natto, fermented cheeses, and animal products, is a proactive step towards supporting long-term health. By incorporating a variety of vitamin k2 foods into a balanced dietary pattern, you can harness the unique benefits of this essential nutrient and contribute to your overall vitality.
References
[1] The National Institutes of Health (NIH) Office of Dietary Supplements (ODS) consumer fact sheet for Vitamin K. https://ods.od.nih.gov/factsheets/VitaminK-Consumer/
[2] Groff JL, Gropper SS. Advanced Nutrition and Human Metabolism. 5th ed. Belmont, CA: Thomson Wadsworth; 2006.
[3] Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press; 2001.
[4] Elder SJ, Haytowitz DB, Howe J, Peterson JW, Booth SL. Vitamin K contents of meat, dairy, and plant-based foods: evidence for nutritional guidelines. J Am Diet Assoc. 2006;106(5):748-53. PubMed abstract
[5] Vermeer C, Shearer MJ, Zittermann A, et al. The potential importance of vitamin K for skeletal and cardiovascular health. Eur J Clin Nutr. 2012;66(12):1223-31. PubMed abstract
[6] Sokoll LJ, Sadowski JA. Vitamin K and coumarin anticoagulants: mechanism of interaction. Annu Rev Nutr. 1996;16:321-40. PubMed abstract
[7] Shearer MJ. Vitamin K. Lancet. 1995;345(8944):229-34. PubMed abstract
[8] Violi F, Lip GY. Vitamin K antagonists: pharmacological differences and clinical implications. Thromb Haemost. 2017;117(7):1207-1217. PubMed abstract
[9] Schlieper G, Westenfeld R, Kruger T, et al. Circulating nonphosphorylated carboxylated matrix gla protein predicts survival in ESRD. J Am Soc Nephrol. 2011;22(3):587-95. PubMed abstract
[10] Borel P, Desmarchelier C, Nowicki M, et al. Study of the intestinal absorption of vitamin K in humans. Am J Clin Nutr. 1998;67(5):814-8. PubMed abstract
[11] Ferland G. Vitamin K. In: Erdman JWJ, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Washington, DC: Wiley-Blackwell; 2012:220-48.
[12] Davidson RT, Hauschka PV, Babson JR, et al. Comparison of plasma phylloquinone and osteocalcin as measures of vitamin K nutritional status in elderly and young adults. Am J Clin Nutr. 1993;58(2):135-41. PubMed abstract
[13] Kaneki M, Hodges SJ, Hosoi T, et al. Japanese fermented soybean food as the major determinant of the large geographic difference in circulating vitamin K2 (menaquinone-7) concentration. Epidemiology. 2001;12(3):337-45. PubMed abstract
[14] Walther B, Karl JP, Booth SL, Boyaval P. Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products. Adv Nutr. 2013;4(4):463-73. PubMed abstract
[15] Thijssen HH, Drittij-Reijnders MJ. Vitamin K status in healthy tissues in rats fed phylloquinone or menaquinone-9. J Nutr. 1996;126(3):557-64. PubMed abstract
[16] U.S. Department of Agriculture, Agricultural Research Service. FoodData Central. https://fdc.nal.usda.gov/
[17] U.S. Food and Drug Administration. CFR – Code of Federal Regulations Title 21. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=101.9
[18] Office of Dietary Supplements, NIH. Dietary Supplement Label Database. https://dsld.od.nih.gov/dsld/index.jsp
[19] Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-7 and phylloquinone pharmacokinetics in healthy women. Nutr J. 2012;11:93. PubMed abstract
[20] Hoy MK, Goldman JD, Peters C, Moshfegh AJ. Usual nutrient intakes from food and beverages, by gender and age, What We Eat in America, NHANES 2009-2012. Food Surveys Research Group Dietary Data Brief No. 12. July 2014. https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/DBrief/12_usual_nutrient_intake_vitD_K_adults_0912.pdf
[21] McKeown NM, Yoshida M, Saltzman E, et al. Habitual vitamin K intakes are associated with vitamin D status in postmenopausal women. J Nutr. 2009;139(8):1521-7. PubMed abstract
[22] Olson RE. Vitamin K intake, status, and recommendations. J Am Diet Assoc. 2009;109(7):1201-9. PubMed abstract
[23] Weber P. Vitamin K and bone health. Nutrition. 2001;17(10):880-7. PubMed abstract
[24] American Academy of Pediatrics Committee on Fetus and Newborn. Controversies concerning vitamin K and the newborn. American Academy of Pediatrics Committee on Fetus and Newborn. Pediatrics. 2003;112(1 Pt 1):191-2. PubMed abstract
[25] Zipursky A. Prevention of vitamin K deficiency bleeding in newborns. Br J Haematol. 1999;104(3):430-7. PubMed abstract
[26] Gonzalez-Dominguez R, Moreno P, Ferrer-Garcia JC, et al. Micronutrient deficiencies in subjects undergoing bariatric surgery. Nutrients. 2020;12(2):495. PubMed abstract
[27] National Osteoporosis Foundation. What is Osteoporosis and What Causes It? https://www.nof.org/patients/what-is-osteoporosis/ Accessed October 26, 2020.
[28] Tsugawa N, Shiraki M, Suhara Y, et al. Vitamin K status and serum osteocalcin in osteoporotic patients. J Bone Miner Metab. 2006;24(4):324-8. PubMed abstract
[29] Booth SL, Tucker KL, Chen H, et al. Dietary vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women. Am J Clin Nutr. 2000;71(6):1201-8. PubMed abstract
[30] Feskanich D, Weber P, Willett WC, et al. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr. 1999;69(1):74-9. PubMed abstract
[31] Knapen MH, Schurgers LJ, Vermeer C. Vitamin K nutritional status is associated with bone mineral density and bone turnover in early postmenopausal women. Am J Clin Nutr. 2007;85(5):1383-8. PubMed abstract
[32] Sato Y, Kanoko T, Satoh K, Iwamoto J. Menatetrenone and vitamin D2 with calcium supplements prevent nonvertebral fracture incidence in elderly women with Alzheimer’s disease. Bone. 2005;36(1):81-7. PubMed abstract
[33] Shearer MJ, Fu X, Booth SL. Vitamin K nutrition, metabolism, and requirements: current concepts and future directions. Adv Nutr. 2012;3(2):182-95. PubMed abstract
[34] Szulc P, Chapuy MC, Meunier PJ, Delmas PD. Serum undercarboxylated osteocalcin is a marker of the risk of hip fracture in elderly women. J Clin Endocrinol Metab. 1996;81(5):1767-70. PubMed abstract
[35] Cockayne S, Adamson J, Lanham-New SA, et al. Vitamin K and risk of fracture: systematic review and meta-analysis of randomised controlled trials. Arch Intern Med. 2006;166(12):1256-61. PubMed abstract
[36] Knapen MH, Drummen NE, Smit E, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499-507. PubMed abstract
[37] Macdonald HM, Mavroeidi A, Fraser WD, et al. Vitamin K1 supplementation has no effect on bone turnover, bone density, or bone ultrasound properties in healthy older men and women over 1 year. J Bone Miner Res. 2008;23(6):817-28. PubMed abstract
[38] Sok DE, Joung JY, Cho JY, et al. Effect of vitamin K supplementation on bone mineral density in elderly women in South Korea: a randomized controlled trial. J Korean Med Sci. 2011;26(11):1393-8. PubMed abstract
[39] European Food Safety Authority. Scientific Opinion on Dietary Reference Values for vitamin K. EFSA Journal 2017;15(12):5051, 49 pp. https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2017.5051
[40] Otsuka F, Goronflot T, Vogt F, et al. Progression of coronary artery calcification and clinical events after acute coronary syndrome. JACC Cardiovasc Imaging. 2017;10(1):22-31. PubMed abstract
[41] Geleijnse JM, Vermeer C, Witteman JC, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100-5. PubMed abstract
[42] Beulens JW, Bots ML, Atsma F, et al. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis. 2009;203(2):489-93. PubMed abstract
[43] Shea MK, Booth SL, Massaro JM, et al. Vitamin K supplementation and progression of coronary artery calcium in older men and women. Am J Clin Nutr. 2009;89(6):1799-807. PubMed abstract
[44] Chatrou ML, Winckers K, Dalmeijer GW, et al. Vitamin K2 and cardiovascular disease: are the observational studies translated into intervention trials? Nutrients. 2020;12(11):3438. PubMed abstract
[45] Natural Medicines. Vitamin K Professional Monograph. In: Natural Medicines Comprehensive Database. Stockton, CA: Therapeutic Research Faculty; 2021. https://naturalmedicines.therapeuticresearch.com/ Accessed October 26, 2020.
[46] Booth SL. Vitamin K: food sources and dietary intakes. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:292-301.
[47] Merli GJ, Brozovic M, Fareed J. Drug interactions with warfarin: recommendations for management. Semin Thromb Hemost. 2004;30(1):105-14. PubMed abstract
[48] Coumadin (warfarin sodium) tablets, for oral use. Prescribing information. Princeton, NJ: Bristol-Myers Squibb Company; 2019. https://packageinserts.bms.com/pi/pi_coumadin.pdf Accessed October 26, 2020.
[49] Alli (orlistat 60 mg capsules). OTC label. Cincinnati, OH: P&G; 2017. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6906f2a7-b994-44b5-b06d-3b36c4b88e2e Accessed October 26, 2020.
[50] Xenical (orlistat) capsules, for oral administration. Prescribing information. South San Francisco, CA: Genentech USA, Inc; 2018. https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/020766s028lbl.pdf Accessed October 26, 2020.
[51] Derosa G, Maffioli P, Ferrari I, et al. Orlistat and fat-soluble vitamins supplementation. Endocrine. 2013;43(1):35-40. PubMed abstract
Disclaimer: This fact sheet provides information that should not take the place of medical advice. We encourage you to talk to your health care providers (doctor, registered dietitian, pharmacist, etc.) about your interest in, questions about, or use of dietary supplements and what may be best for your overall health.
