Introduction

Vitamin K2, also known as menaquinone, is a fat-soluble nutrient that plays a pivotal role in bone and cardiovascular health. While many are familiar with vitamin K’s function in blood clotting, K2 supports calcium utilization in the skeleton and helps maintain healthy arteries.

In this comprehensive article, we explore the science, dietary sources, and established health effects of vitamin K2. By the end, you will understand why this nutrient is essential and learn practical ways to incorporate it into your daily routine.

Role in the Body

Vitamin K2 functions as a cofactor for the enzyme gamma-glutamyl carboxylase, which modifies specific proteins by adding carboxyl groups. This process—known as gamma-carboxylation—enables these proteins to bind calcium effectively. Without vitamin K2, calcium-binding proteins remain inactive, impairing their ability to regulate mineralization in bones and blood vessels.

There are several forms of vitamin K2, called menaquinones, designated MK-4 through MK-13. The most studied in human health are MK-4, typically found in animal tissues, and MK-7, produced by bacterial fermentation and abundant in fermented foods like natto.

Specific Functions

Vitamin K2 supports multiple biological processes:

• Activation of osteocalcin, a protein synthesized by osteoblasts, which helps bind calcium to the bone matrix. (Schurgers et al., 2007)

• Regulation of matrix Gla protein (MGP), a critical inhibitor of vascular calcification that prevents calcium deposits in arterial walls. (Vermeer, 2002)

• Facilitation of prothrombin activation in the liver, contributing to proper blood coagulation, though K1 is the primary form for hemostasis.

Effects of Deficiency

Insufficient vitamin K2 can lead to undercarboxylation of key proteins, disrupting calcium metabolism. Common consequences include:

• Reduced bone mineral density, increasing the risk of osteoporosis and fractures. Low K2 intake has been associated with higher fracture rates in postmenopausal women. (Gast et al., 2009)

• Progressive calcification of arteries, contributing to stiffness and atherosclerosis. Higher dietary K2 intake correlates with lower coronary calcification and cardiovascular mortality. (Geleijnse et al., 2004)

Dietary Sources

Because vitamin K2 is mainly produced by bacteria and accumulates in animal or fermented products, obtaining it through diet requires attention to specific foods.

Best Food Sources

• Natto (fermented soybeans) — richest source of MK-7, one serving provides over 1,000 µg.

• Hard cheeses (e.g., Gouda, Edam) — fermented by bacteria that produce MK-8 and MK-9, offering 50–100 µg per 100 g.

• Soft cheeses (e.g., Brie, Camembert) — moderate K2 levels, around 30–50 µg per 100 g.

• Egg yolks — contain MK-4, roughly 15 µg per yolk, varying with hen’s diet.

• Grass-fed dairy (butter, yogurt) — variable MK-4 content, typically 5–20 µg per 100 g.

• Organ meats (liver, kidney) — MK-4 levels of 30–50 µg per 100 g.

• Chicken, pork, and beef — lean cuts provide 5–15 µg of MK-4 per 100 g, depending on diet and fat content.

Supplementation

While a balanced diet can supply vitamin K2, certain individuals may benefit from supplements:

• Older adults and postmenopausal women at risk of osteoporosis, especially if dietary intake is low.

• Individuals with malabsorption issues (e.g., celiac disease, Crohn’s disease) who have difficulty absorbing fat-soluble vitamins.

• Vegans and vegetarians who do not consume fermented animal products; they may rely on natto or K2 supplements derived from bacterial fermentation.

• People on long-term antibiotic therapy, which may disrupt gut bacteria responsible for K2 production.

Supplement options include MK-4 (short half-life, often dosed multiple times daily) and MK-7 (long half-life, once-daily dosing). A typical supplemental dose ranges from 45 µg to 200 µg per day for MK-7, while MK-4 doses can vary from 150 µg to 1 mg daily, depending on clinical goals. (Schurgers & Vermeer, 2000)

Health Benefits

Bone Health: By activating osteocalcin, K2 improves bone mineralization. A meta-analysis in the Journal of Bone and Mineral Metabolism found that MK-4 supplementation reduced vertebral fracture risk in postmenopausal women with osteoporosis. (Abe et al., 2000)

Cardiovascular Health: K2’s role in MGP carboxylation helps prevent arterial calcification. The Rotterdam Study showed participants with the highest dietary K2 intake had a significantly lower rate of severe aortic calcification and lower coronary heart disease mortality over a 7- to 10-year follow-up. (Geleijnse et al., 2004)

“Vitamin K2 is emerging as a key factor in maintaining vascular elasticity and reducing calcific plaque formation.” — Dr. Cees Vermeer, Maastricht University

Daily Requirements

Official guidelines do not specify separate recommendations for K2. Adequate Intake (AI) for total vitamin K (K1 plus K2) is defined by age and sex:

• Children (1–13 years): 30–45 µg per day total vitamin K.

• Adolescents (14–18 years): 60–75 µg per day total vitamin K.

• Adults (19+ years): 90 µg per day for women, 120 µg per day for men as AI for total vitamin K, with at least 45–75 µg from K2-rich sources to support bone and cardiovascular health.

• Pregnant and lactating women: 90–100 µg per day total vitamin K; aiming for 50–75 µg from K2 sources.

Tips for Incorporation

Integrating vitamin K2 into daily meals can be easy and delicious:

• Start the day with a natto bowl or add natto to stir-fries.

• Add slices of aged cheese (Gouda or Edam) to salads, sandwiches, or as a snack with fruits and nuts.

• Use grass-fed butter for cooking or finish steamed vegetables with a pat of butter.

• Include organ meats like liver pâté on toast or in meatballs once a week.

• Rotate eggs from pasture-raised hens into omelets and frittatas.

• Complement meals with healthy fats (olive oil, avocado) to aid fat-soluble vitamin absorption.

• Consider a high-quality K2 supplement, particularly MK-7 form, if dietary intake is insufficient.

Conclusion

Vitamin K2 directs calcium to the skeleton, guards against arterial calcification, and supports overall bone and cardiovascular health. By understanding its roles, identifying rich dietary sources, and adopting practical strategies for incorporation, you can harness the benefits of K2 for long-term wellness.

Call to Action: Prioritize vitamin K2 in your diet today—whether through fermented foods, grass-fed dairy, or targeted supplementation—and take a proactive step toward stronger bones and healthier arteries.

Disclaimer: This article is for informational purposes and should not be considered medical advice. Always consult a healthcare professional or a registered dietitian before making significant changes to your diet or starting any supplementation.