Vitamin K2: Side Effects and Why There Is No Upper Limit

September 28, 2026about 15 minutesby mybody®x Editorial & Expert Team

In This Article

Does Vitamin K2 Have Side Effects? What Studies Show

The US Pharmacopeia sees no serious health risk from MK-7 as a dietary supplement (US Pharmacopeia; Marles et al., Nutrition Reviews, 2017). Across 14 studies involving 1,533 participants, adverse events—that is, health incidents during a study—were no more common with vitamin K (Li et al., Frontiers in Nutrition, 2023).

Behind the abbreviation MK-7 is menaquinone-7, a form of vitamin K2. Menaquinones are the K2 forms, while phylloquinone is the technical name for vitamin K1 (EFSA, 2017). The article What Is Vitamin K? K1 and K2 at a Glance explains the fundamental differences between the two. Here, we look at what studies tell us about K2's tolerability.

The US Pharmacopeia, the body behind the United States Pharmacopeia, has issued a safety assessment of MK-7. Its conclusion: based on the data reviewed, MK-7 taken as a dietary supplement is associated neither with a serious health risk nor with other public health concerns (US Pharmacopeia; Marles et al., Nutrition Reviews, 2017). This assessment does not apply to people taking certain anticoagulants—we’ll come back to that shortly.

The second source is a meta-analysis, which combines the results of several studies. Li et al. analyzed 14 randomized trials involving a total of 1,533 participants (Li et al., Frontiers in Nutrition, 2023). Randomized means that chance determines who receives vitamin K and who is placed in the comparison group. The authors found no significant, or statistically reliable, difference in adverse events between the groups.

To put this in context, it is important to consider what these studies investigated. They looked at vitamin K and vascular calcification, primarily in patient groups such as people with kidney disease (Li et al., Frontiers in Nutrition, 2023). They measured surrogate outcomes, such as the amount of calcium in the coronary arteries, rather than disease progression. According to the authors, only more rigorously designed studies can show whether vitamin K slows calcification.

The third source concerns the blood of healthy people. In a study of 42 healthy individuals between 18 and 45 years old, participants received different daily amounts of MK-7 or a placebo, a dummy preparation without an active ingredient (Theuwissen et al., British Journal of Nutrition, 2012). The researchers found no adverse effects on thrombin generation. Thrombin is an enzyme involved in blood clotting; the amount produced in a laboratory is considered a measure of how ready the blood is to clot.

There are limitations to the strength of this evidence: there were six people in each group, and the researchers measured a laboratory value, not thrombosis (Theuwissen et al., British Journal of Nutrition, 2012). So the finding supports the statement that MK-7 did not increase the blood’s tendency to clot in healthy people in a laboratory setting. Nothing more.

The evidence in numbers

Source: Li et al., Frontiers in Nutrition, 2023 · Theuwissen et al., British Journal of Nutrition, 2012 · BfR, 2021

Do the findings on vitamin K2 apply to everyone?

No. Different rules apply to people who take vitamin K antagonists. These are anticoagulants that counteract the effects of vitamin K, for example those containing the active ingredients phenprocoumon or warfarin. In a study involving healthy people who received one such active ingredient for this purpose, even small amounts of MK-7 changed how strongly the medication worked in some participants (Theuwissen et al., Journal of Thrombosis and Haemostasis, 2013). The implications are discussed in the chapter on anticoagulants.

Why is there no upper limit for vitamin K2?

Because the data were insufficient: no tolerable upper limit was derived for vitamin K, and this therefore also applies to K2 (BfR, 2021).

A tolerable upper limit, internationally known as the Tolerable Upper Intake Level, or UL for short, is the highest total daily intake of a nutrient at which an expert authority still expects no harm to health. There is no such value for vitamin K. The German Federal Institute for Risk Assessment gives the reason in a single sentence (BfR, 2021).

The absence of an upper limit does not mean that vitamin K is harmless in any amount. It means that there was not enough data to set a limit. Regarding toxicity, the BfR states: “The available studies indicate low acute and chronic toxicity of orally administered vitamin K.” (BfR, 2021) Toxicity means harmfulness; acute refers to a single intake, while chronic refers to intake over a long period.

Why has the EFSA not set a reference value for vitamin K2?

Because, in the view of its expert panel, there is not enough knowledge about K2 for this: The European Food Safety Authority (EFSA) sets a reference value only for vitamin K1 (EFSA, 2017). The panel considers the data on menaquinones, the forms of K2, insufficient.

The value for K1 is an estimate, called Adequate Intake in English: a daily amount that the authority considers sufficient for adequate intake. It is 1 µg per kilogram of body weight per day, or 70 µg daily for adults (EFSA, 2017). For K2, there is therefore neither a separate daily requirement nor an upper limit (EFSA, 2017; BfR, 2021). Both gaps have the same cause: insufficient data.

What does overdose mean for vitamin K2?

With vitamin K2, overdose mainly means that it can weaken the effect of anticoagulants (BfR, 2021). The BfR’s proposed maximum levels are based on this interaction, not on toxicity.

This shifts the question of “too much.” For K2, it is not a question of the amount at which the body is harmed, but whether a medication is involved whose effect vitamin K can weaken. For people not taking such medication, the sources in the first chapter describe no serious health risk (US Pharmacopeia; Marles et al., Nutrition Reviews, 2017).

The BfR quantifies how strongly K2 acts compared with K1 using data on acenocoumarol, an active substance in the vitamin K antagonist group: “The potency of vitamin K2 in reducing the therapeutic effect of acenocoumarol was therefore approximately 3.5 times that of vitamin K1.” (BfR, 2021) Accordingly, the proposed maximum for K2 is lower than that for K1.

Does vitamin K2 build up in the blood?

For the MK-7 form, yes: with longer-term use, seven to eight times longer (Schurgers et al., Blood, 2007). The researchers compared K1 with MK-7 and describe MK-7 as having a very long half-life, meaning it takes a long time for half of the substance to disappear from the blood. As a result, blood levels are much more stable.

In healthy people, Theuwissen et al.’s study found no adverse effects on thrombin generation with daily MK-7 (Theuwissen et al., British Journal of Nutrition, 2012). For people taking vitamin K antagonists, however, MK-7’s long persistence is something to discuss with their healthcare provider.

What maximum amount of vitamin K2 does the BfR propose?

For dietary supplements, the BfR proposes a maximum of 25 µg of vitamin K2 and 80 µg of vitamin K1 per product’s recommended daily intake (BfR, 2021). This is a recommendation from an expert authority, not current law.

A proposed maximum level indicates how much of a nutrient a single product should contain at most, in the authority’s view, based on the recommended daily serving. This is the daily amount that the manufacturer specifies on the packaging. So the proposal concerns the content of a product, not all the vitamin K you consume throughout the day (BfR, 2021). It is not a recommendation on how much to take, either.

The BfR derived these values from interactions with anticoagulants, not from toxicity (BfR, 2021). The starting point is the daily amount at which the INR value measurably decreases: 150 µg of vitamin K1 or 45 µg of vitamin K2 (BfR, 2021). INR, or International Normalized Ratio, is a standardized laboratory value for blood clotting time. If it decreases while taking an anticoagulant, the blood clots faster: the medication has a weaker effect. The BfR applies an uncertainty factor of approximately 2 to this threshold, providing a safety margin for what the data do not capture precisely (BfR, 2021).

Maximum levels and reference value · Source: BfR, 2021; EFSA, 2017

For other foods to which vitamins are added, the proposal is: no added vitamin K (BfR, 2021). When updating its proposed maximum levels in 2024, the BfR adjusted the values for other nutrients, but not for vitamin K (BfR, 2024).

For information on combining vitamin D3 with vitamin K and how to dose them, see the article Combining Vitamins D3 and K2. Here, we’ll focus on vitamin K.

What applies to vitamin K2 and anticoagulants?

Anyone taking anticoagulant medication should discuss any questions about vitamin K with their healthcare provider. The BfR puts it this way: “People taking anticoagulant medication should seek medical advice before consuming vitamin K-containing dietary supplements.” (BfR, 2021)

The article Vitamin K and Blood Clotting explains whether vitamin K2 makes blood thicker or thinner. It covers clotting and thrombosis, while this article focuses on side effects and maximum amounts.

The mechanism in brief: The liver needs vitamin K to produce clotting factors, proteins that enable blood to clot (Schurgers et al., Blood, 2007). Vitamin K antagonists counteract this function and thereby inhibit clotting. Additional vitamin K can weaken their effect (BfR, 2021).

A study involving 18 healthy people who received the vitamin K antagonist acenocoumarol for the study shows how sensitive this balance can be (Theuwissen et al., Journal of Thrombosis and Haemostasis, 2013). Even small amounts of MK-7 altered the anticoagulant’s effect in some participants (Theuwissen et al., Journal of Thrombosis and Haemostasis, 2013). Theuwissen et al. conclude that MK-7 supplements should be avoided while taking vitamin K antagonists.

The study used acenocoumarol, not phenprocoumon (Theuwissen et al., Journal of Thrombosis and Haemostasis, 2013). The BfR warning applies regardless to everyone taking anticoagulant medication (BfR, 2021).

Check with your doctor beforehand whether a vitamin K supplement is compatible with your medication. Do not change your current medication without consulting them. If you notice any symptoms or are unsure whether one of your medications is affected, your primary care practice is the first place to turn.

How much vitamin K2 comes from food?

In the Heidelberg EPIC study, the median daily intake was 93.6 µg of vitamin K1 and 34.7 µg of vitamin K2 (BfR, 2021). EPIC Heidelberg is the Heidelberg section of a European nutrition study; the BfR draws on its data in its statement.

Median means that half of the participants were above this value and half below it. The figure describes the midpoint of the group, not the average and not one individual’s intake.

Regarding intake, the BfR notes: “Dietary intake data from Germany provide no indication of an inadequate vitamin K supply in the general population and/or in specific age groups.” (BfR, 2021) There is no separate daily requirement for K2 against which to measure the 34.7 µg figure (EFSA, 2017; BfR, 2021).

The table of vitamin K in foods shows how much vitamin K1 and K2 different foods provide.

What can a vitamin K2 supplement claim?

Only health claims approved under EU Regulation 432/2012, and only in the prescribed wording. One such claim for vitamin K in combination with vitamin D is: “Vitamin D and vitamin K contribute to the maintenance of normal bones.”

Health claims are statements about the effects of a nutrient that manufacturers are allowed to use in advertising. Only certain formulations, such as “contributes to,” are approved; anything beyond that is impermissible advertising. A K2 supplement that promises more goes beyond these limits.

mybody®x (MYBODY Lab GmbH) offers vitamin K2 in the Vitamin D3 K2 Complex Shield: micellar drops with vitamin D3 and vitamin K2, supplemented with selenium. Shield is a food supplement. It is not intended to treat side effects or affect blood clotting. People taking anticoagulant medication should also follow the BfR's advice to seek medical guidance beforehand (BfR, 2021).

Who should be concerned about vitamin K2 side effects?

Especially for people taking vitamin K antagonists: The BfR bases its proposed maximum levels on interactions with these medications (BfR, 2021).

The sources paint a reassuring picture for healthy people. The US Pharmacopeia sees no serious health risk with MK-7 (US Pharmacopeia; Marles et al., Nutrition Reviews, 2017), and in healthy people, MK-7 had no adverse effects on thrombin generation (Theuwissen et al., British Journal of Nutrition, 2012). The absence of a tolerable upper limit reflects the available data and is not a free pass (BfR, 2021).

So there is no specific amount at which an overdose begins. For products, the BfR proposes a limit based on the recommended daily serving of a supplement, not on your total intake (BfR, 2021). If you take anticoagulants, consult your healthcare provider. If you’re unsure, take the supplement package with you to your family doctor’s office. They can clarify what applies to you.

Frequently asked questions

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Sources

1. German Federal Institute for Risk Assessment: Proposed maximum levels for vitamin K in foods, including dietary supplements (as of 2021) – bfr.bund.de
2. Marles et al., US Pharmacopeia: Safety of menaquinone-7, Nutrition Reviews (as of 2017) – europepmc.org
3. Li et al.: Vitamin K and vascular calcification, Frontiers in Nutrition (as of 2023) – europepmc.org
4. Theuwissen et al.: MK-7 while taking anticoagulants, Journal of Thrombosis and Haemostasis (as of 2013) – europepmc.org

The proposed maximum levels, their rationale, and the statement that there is no upper limit are based on [1]. The warning about anticoagulants and the intake data from EPIC Heidelberg come from the same statement. The safety assessment of MK-7 comes from [2]. The analysis of adverse events comes from [3], and the study involving people taking anticoagulants is [4]. The reference value for vitamin K1 is given by the EFSA Journal (EFSA, 2017); the half-life of MK-7 comes from a study in Blood (Schurgers et al., Blood, 2007). Thrombin generation in healthy people comes from the British Journal of Nutrition (Theuwissen et al., British Journal of Nutrition, 2012), and the fact that the proposed levels remain unchanged comes from the BfR update (BfR, 2024). All sources accessed on 28.09.2026. Product information for Vitamin D3 K2 Complex Shield: as of 28.09.2026; subject to change.