Which is better, K1 or K2?

December 5, 2025 •

4 min read

Less than 10% of vitamin K1 found in plants is actually absorbed by the body, highlighting a key difference in bioavailability between the two forms. For those asking, "Which is better, K1 or K2?", the answer depends on your specific health goals, as each form has unique strengths and purposes in the body.

Quick Summary

This article explores the fundamental differences between vitamin K1 and vitamin K2, examining their functions, food sources, absorption rates, and distinct benefits for bone and cardiovascular health. It offers a side-by-side comparison to clarify which vitamin is most effective for different health outcomes.

Key Points

Different Functions: K1 is primarily for liver-based blood clotting, while K2 is more focused on bone mineralization and cardiovascular protection in extra-hepatic tissues.
Distinct Sources: K1 is found mostly in leafy greens, whereas K2 is abundant in fermented foods (like natto) and animal products.
Superior Bioavailability of K2: Vitamin K2 is generally absorbed better and remains in circulation longer than K1, allowing it to reach a wider range of tissues.
Both are Necessary: Neither K1 nor K2 is definitively "better"; both are essential, fulfilling unique and vital roles in the body.
Dietary Strategy: The best approach is to consume a balanced diet that includes sources of both K1 and K2 to ensure comprehensive vitamin K benefits.
Supplementation Consideration: While most people get enough K1 from their diet, targeted K2 supplementation may be beneficial for bone and heart health, particularly for those with inadequate dietary intake.

Understanding the Vitamin K Family

Vitamin K isn't a single nutrient but a family of fat-soluble vitamins crucial for blood clotting, bone metabolism, and heart health. The two main types found in the human diet are vitamin K1 (phylloquinone) and vitamin K2 (menaquinones). While both share the same core function of activating key proteins, their chemical structures, sources, and distribution within the body differ significantly, leading to distinct health impacts.

Vitamin K1: The Coagulation Specialist

Vitamin K1, primarily sourced from leafy green vegetables, is known as the "blood clotting vitamin". When you consume K1 from a cup of spinach or kale, it's quickly and preferentially taken up by the liver. The liver uses it to activate proteins involved in the coagulation cascade, a vital process that prevents excessive bleeding. Because of its role in blood clotting, people on blood-thinning medication like warfarin must maintain a consistent intake of K1 to avoid interference with their medication. However, the bioavailability of K1 from plant sources is relatively low, meaning a large portion is not effectively absorbed by the body.

Vitamin K2: The Bone and Heart Advocate

In contrast, vitamin K2 is a collection of subtypes, known as menaquinones (MKs), found predominantly in fermented foods and animal products. Unlike K1, which has a short circulation time, some forms of K2—particularly MK-7—have a longer half-life, allowing them to remain active in the blood for days. This prolonged presence enables K2 to be distributed to extra-hepatic tissues like bones and blood vessel walls, where it performs functions that K1 cannot.

K2's primary extra-hepatic function involves activating two key proteins: osteocalcin, which incorporates calcium into bones, and Matrix Gla Protein (MGP), which prevents calcium from accumulating in soft tissues like arteries. This calcium-directing ability is why K2 is often highlighted for its potential to improve bone density and protect against arterial calcification and heart disease.

Comparison Table: K1 vs. K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Function	Blood clotting in the liver.	Bone mineralization and prevention of arterial calcification.
Main Sources	Leafy green vegetables (spinach, kale), broccoli, vegetable oils.	Fermented foods (natto, sauerkraut), animal products (egg yolks, liver, grass-fed butter), certain cheeses.
Absorption	Poorly absorbed from plant sources; absorption improved with dietary fat.	Generally better absorbed, especially the MK-7 subtype, which is often found with fats.
Bioavailability	Lower; quickly cleared by the liver.	Higher and longer-lasting in circulation, especially long-chain MKs like MK-7.
Circulation	Shorter half-life, active for several hours.	Longer half-life (up to several days), allowing wider distribution.
Health Focus	Strong evidence for blood coagulation; less impact on bone/heart health.	Strong evidence for extra-hepatic benefits, especially for bone and heart health.
Supplements	Often used for specific blood-clotting issues.	Often used for supporting bone and cardiovascular health.

How Your Body Uses Each Vitamin K Type

The metabolic fate of K1 and K2 is a crucial point of distinction. Once absorbed, K1 is rapidly shuttled to the liver where it is used to activate coagulation proteins. This process is essential for healing wounds, but it leaves little K1 available for other areas of the body. K2, however, particularly the long-chain versions synthesized by bacteria, is better equipped to travel throughout the body. After absorption, K2 gets incorporated into lipoproteins and can be delivered to various extra-hepatic tissues, explaining its superior performance in areas like bone and vascular health.

The Importance of Both in Your Diet

The question of which is better, K1 or K2, is misleading because both are essential and have distinct roles. K1 ensures you can stop bleeding effectively, while K2 works behind the scenes to maintain long-term bone and heart health. While your gut bacteria can convert some K1 to K2, the process is not efficient enough to meet all your K2 needs. Therefore, aiming for dietary sources of both is the most prudent approach. For instance, you could start your day with K2-rich egg yolks and later add a spinach salad with an oil-based dressing to maximize K1 absorption.

Conclusion: Tailoring Your Intake to Your Needs

Ultimately, there is no single "better" vitamin between K1 and K2, as they serve different, critical purposes. For blood clotting, K1 is the immediate and indispensable factor used by the liver. For longer-term maintenance of healthy bones and supple arteries, K2, with its better absorption and extra-hepatic distribution, holds a clear advantage. A balanced diet rich in leafy greens for K1, alongside fermented foods or animal products for K2, is the optimal strategy for overall health. Individuals with specific health concerns, such as osteoporosis or heart disease risk, should discuss supplementation with a healthcare provider, especially as current dietary recommendations primarily focus on K1.

Bone Health Network is an authoritative resource that can provide additional context on the importance of vitamin K for skeletal health.

Frequently Asked Questions

The main differences are their sources, how the body uses them, and where they are distributed. K1, from plants, is mainly used by the liver for blood clotting, while K2, from fermented and animal foods, is better absorbed and distributed to bones and arteries for calcium regulation.

Yes, research suggests K2 is more effective for bone health than K1. K2 activates osteocalcin, a protein that directs calcium into your bones, which is critical for bone mineralization and strength.

Evidence indicates that K2 may be more beneficial for heart health by activating proteins that prevent calcium from depositing in the arteries. While K1 has a minor role, K2’s ability to prevent arterial calcification is more pronounced in studies.

K1 is abundant in leafy green vegetables like kale, spinach, and broccoli. K2 is found in fermented foods such as natto and sauerkraut, and animal products like egg yolks, liver, and some cheeses.

Yes, bacteria in the gut can convert some K1 into K2. However, this conversion process is not efficient enough to provide all the K2 needed for optimal bone and heart health.

A balanced diet typically provides sufficient K1. However, since K2 is less common in a Western diet, supplementation may be beneficial, especially for those with concerns about bone density or cardiovascular health. Always consult a healthcare provider before starting any new supplement.

Yes, if you take blood thinners like warfarin, you should maintain a consistent intake of both K1 and K2 and consult your doctor before making significant dietary changes or starting supplements. Sudden changes in vitamin K intake can interfere with the medication's effectiveness.