How much is too much vitamin K in one day? Unpacking safe intake

November 17, 2025 •

3 min read

While there is no established Tolerable Upper Intake Level (UL) for the natural forms of vitamin K (K1 and K2) due to their low toxicity, the synthetic version, K3, is banned for human consumption due to safety concerns. Understanding how much is too much vitamin K in one day depends largely on the form and an individual's health status, especially for those on anticoagulant medication.

Quick Summary

Natural vitamin K1 and K2 have no known toxicity from food or supplements, so no official upper limit exists. However, high intake can significantly interfere with anticoagulant medications like warfarin. Excessive synthetic vitamin K3 is toxic, causing severe side effects, and is no longer used clinically.

Key Points

No Official Upper Limit for Natural Forms: For healthy individuals, there is no established Tolerable Upper Intake Level (UL) for natural vitamin K1 and K2 from food or supplements due to low toxicity.
Synthetic Form is Dangerous: The synthetic vitamin K3 (menadione) is toxic and is no longer used in human supplements; toxicity is associated with symptoms like jaundice and hemolytic anemia.
Warfarin Users Beware: High or inconsistent vitamin K intake is very dangerous for those on anticoagulant drugs like warfarin, as it can interfere with medication effectiveness and increase clotting risk.
Adequate Intake is the Goal: Instead of worrying about excess, focus on meeting the Adequate Intake (AI) of 120 mcg/day for adult men and 90 mcg/day for adult women through a balanced diet.
Focus on Dietary Sources: The safest way to consume vitamin K is through food, particularly leafy greens for K1 and fermented foods or animal products for K2.
Monitor During Specific Conditions: Those with malabsorption disorders, on certain long-term antibiotics, or post-bariatric surgery may need to monitor their intake more closely with a doctor.

Understanding Vitamin K: Not All Forms Are Equal

Vitamin K is a fat-soluble vitamin crucial for blood clotting and bone health. It exists in various forms, including phylloquinone (K1) and menaquinones (K2). A synthetic form, menadione (K3), is considered toxic and is not used in supplements.

The Lack of a Tolerable Upper Intake Level (UL)

Natural forms of vitamin K (K1 and K2) from food or supplements are not linked to toxicity in healthy individuals, which is why no Tolerable Upper Intake Level (UL) has been set. The body manages natural vitamin K efficiently, and any potential side effects are usually mild, such as gastrointestinal upset.

The Synthetic Exception: Vitamin K3 (Menadione)

Unlike K1 and K2, the synthetic menadione (K3) is toxic and has been associated with severe reactions like liver damage and hemolytic anemia, particularly in infants. For this reason, it is prohibited in many countries, including the U.S..

Adequate Intake (AI) Recommendations

While there is no UL for natural vitamin K, Adequate Intake (AI) levels have been set based on average daily consumption by healthy individuals. According to the NIH, the AI for adults is:

Adult Men (19+ years): 120 mcg/day
Adult Women (19+ years): 90 mcg/day
Pregnant or Breastfeeding Women (19+ years): 90 mcg/day

Most people can meet these recommendations through diet, ensuring proper blood clotting and bone health.

The Critical Link with Anticoagulant Medication

For individuals taking anticoagulants like warfarin, consuming too much or inconsistent amounts of vitamin K can be dangerous. Warfarin interferes with vitamin K's role in activating clotting factors. High vitamin K intake can reduce warfarin's effectiveness, increasing clot risk. Conversely, a decrease in intake can heighten warfarin's effect, raising bleeding risk. Those on warfarin need to maintain consistent vitamin K intake under medical guidance.

Who Needs to Monitor Their Vitamin K Intake?

Certain individuals should be particularly mindful of their vitamin K intake, primarily due to factors other than toxicity from high doses:

Patients on Warfarin: Consistent intake is vital for maintaining the drug's efficacy.
Newborns: Given their low vitamin K stores, a standard injection at birth prevents Vitamin K Deficiency Bleeding (VKDB).
Individuals with Malabsorption Issues: Conditions like celiac disease or cystic fibrosis can impair vitamin K absorption.
Patients on Long-term Antibiotics: Extended use of certain antibiotics may disrupt gut bacteria that produce K2.

Comparing Different Vitamin K Forms


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)	Vitamin K3 (Menadione)
Source	Plant foods	Fermented foods, animal products	Synthetic (banned for humans)
Absorption	Poor from plants; better with fats	Generally better absorbed	N/A
Toxicity Risk	Very low; no UL	Very low; no UL	Highly toxic
Half-Life	Short; liver focus	Longer; broader tissue effects	N/A
Key Functions	Blood clotting	Bone, cardiovascular, immune health	N/A

Sources of Natural Vitamin K

Getting vitamin K from food is the recommended approach for most people:

Vitamin K1-rich foods: Leafy greens like kale, spinach, and collard greens, as well as broccoli.
Vitamin K2-rich foods: Natto, certain cheeses, eggs, and chicken.

Conclusion: Safe Intake is All About Context

For healthy individuals, consuming natural vitamin K1 and K2 is safe, with no upper limit established due to low toxicity. The primary concern with high vitamin K intake is its interaction with anticoagulant medications like warfarin, where consistency is key to avoid dangerous fluctuations in clotting risk. The synthetic vitamin K3, menadione, is toxic and not for human consumption. A balanced diet is typically sufficient for most people to meet their vitamin K needs. Always consult a healthcare provider before making changes to supplement intake, especially if you have existing health conditions or take medication. For more information, the NIH Office of Dietary Supplements website is a valuable resource.

Frequently Asked Questions

No, it is extremely rare and almost impossible to consume a toxic amount of vitamin K from food sources alone. Natural vitamin K1 and K2 are considered safe even in high doses from the diet.

Toxicity from natural vitamin K is not a concern, but the synthetic vitamin K3 (menadione), which is banned for human use, can cause jaundice, hemolytic anemia, and liver damage, especially in infants.

For most healthy individuals, vitamin K1 and K2 supplements at recommended doses are safe. However, individuals on blood thinners like warfarin should consult a doctor before starting any supplement.

For those on warfarin, the key is consistency rather than a specific amount. Drastic changes in vitamin K intake can interfere with the medication. It is essential to work with a healthcare provider to manage a consistent intake.

Both natural vitamin K1 and K2 have very low toxicity and no established upper intake level. The main difference lies in their absorption and distribution in the body, with K1 primarily benefiting the liver and K2 having a longer half-life and broader tissue distribution.

While vitamin K promotes blood clotting, excessive intake does not typically cause inappropriate clotting in healthy individuals. The concern regarding clotting risk is primarily for people on anticoagulant medication whose intake interferes with their drug's effect.

Side effects from natural vitamin K (K1 and K2) at suggested doses are rare. Less common issues may include mild digestive upset like nausea or diarrhea.