Amount of Evidence: Very High Potential Benefits: High Safety: Very High
TABLE OF CONTENTS
What is vitamin K?
Vitamin K is a fat-soluble essential vitamin that comes in 2 main forms: K1 and K2. This nutrient is essential for improving bone health and regulating blood clotting. However, these are just two of the many potential benefits of vitamin K. In this article, we will look at vitamin K’s main benefits, potential side effects, and how to use it the right way.
Potential benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. In general, the higher the dose you take, the more pronounced the effects will be. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting a vitamin K deficiency – A severe vitamin K deficiency can have a terrible impact on health and overall quality of life. The main symptom of vitamin K deficiency is excessive bleeding (from the nose, wounds, and internal bleeding). If you experience some of these or you know your vitamin K levels are too low, fixing a deficiency is definitely the main benefit of the supplement. Fortunately, a severe deficiency is not as common as a deficiency of many other nutrients. Unfortunately, optimal levels of the vitamin are even more uncommon.
Reduced risk for cancer – While this effect is most notable when it comes to liver cancer, it likely applies to other types of cancer as well. It is important to note that this effect has often been correlated with very high doses of the vitamin and may not apply to lower doses to a significant degree. This effect is specific to the MK-4 form but other forms of vitamin K can convert to MK-4.
Improved bone health – Vitamin K supplements have been shown to reduce bone fracture risk and significantly increase bone mineral density. Older people will benefit from this effect the most but it applies to young people as well. The effect is most notable when you pair vitamin K supplements with vitamin D.
Reduced all-cause mortality – Those with optimal levels of the vitamin live longer than those with suboptimal levels.
Improved blood clotting – The reason the vitamin is called vitamin K is that K is the first letter of the German word koagulation (blood clotting). The vitamin itself doesn’t clot blood, it simply makes the process possible. This means that if you get more than enough vitamin K, you do not need to worry that your blood would clot too much. The exception to this rule is if you take anti-clotting (anticoagulant) medication since the vitamin can completely suppress its effects.
Minor benefits
Improved calcium absorption – Supplementing with vitamin K appears to significantly improve calcium absorption. More specifically, it helps move calcium from the wrong places (such as kidneys and arteries) to the right places (such as bones and teeth). This effect is directly responsible for many of the other benefits.
Improved insulin sensitivity – Vitamin K supplementation leads to a slight improvement in insulin sensitivity. While this benefit has only been observed in studies done on MK-4, it likely applies to other forms as well.
Reduced risk of kidney stones – This is because the vitamin helps keep calcium out of your kidneys.
Improved cardiovascular health – The vitamin can be very beneficial for improving cardiovascular health. This is mainly because it can pull excess calcium from the arteries and soft tissues where it doesn’t belong. The effect is most pronounced when vitamin K is paired with vitamin D.
Lowered risk of falling – The risk goes down significantly for older people who take the supplement. While this benefit may not seem too important (especially if you are young), falls become a huge problem for older people. This benefit appears to be enhanced by taking vitamin K along with calcium and vitamin D.
Increased testosterone – While the evidence for this effect is somewhat limited, the supplement does appear to increase testosterone to a small degree. This benefit may only apply to MK4 but other forms could positively affect testosterone levels as well.
Improved PCOS – Vitamin K helps bring high levels of male hormones found in women with polycystic ovarian syndrome (PCOS) back down to normal.
Reduced reddening of the skin – Topical vitamin K can reduce the reddening of the skin and bags under the eyes to a certain degree.
Preventing vitamin D toxicity – Vitamin K can lower the side effects associated with too high vitamin D levels, such as hypercalcemia.
Improved cognition – The vitamin has been shown to have neuroprotective effects. This effect is most notable in older people, where the supplement has been shown to improve memory and learning.
Unproven benefits
The effect of vitamin K on these parameters is either not sufficiently researched or the science shows little to no efficacy in these areas.
Triglycerides – No significant influence has ever been noted.
Cholesterol – The vitamin does not directly influence HDL or LDL cholesterol levels.
VO2 max – The supplement does not directly improve your VO2 max.
Total antioxidant capacity (TAC) – No notable effect has ever been noted.
Strength – Vitamin K supplements do not directly help you gain strength or muscle mass faster.
Sleep quality – The supplement does not appear to increase sleep quality. It also does not affect sleep duration.
Bruising – The evidence on whether or not the vitamin can help with bruising is mixed.
Power output – Vitamin K does not influence power output during cardio or resistance training. It does not impact endurance either.
Fatigue – The supplement does not reduce symptoms of fatigue.
Stress and anxiety – Unfortunately, no effect has ever been noted. Vitamin K supplements do not directly impact cortisol levels. What it can do is protect your bones from cortisol-induced damage.
Weight loss – The vitamin does not directly increase fat loss or weight loss. However, osteocalcin (one of the major vitamin K-dependent proteins) appears to have anti-obese properties. The best form of the vitamin for forming osteocalcin appears to be MK-7 but this benefit likely applies to the other forms as well.
Food intake – Vitamin K does not increase nor decrease your appetite for food.
Inflammation – No significant effect on CRP or other markers of inflammation has been observed.
Metabolic rate – The supplement does not speed up your metabolism.
Pain – The vitamin doesn’t reduce the intensity of physical pain.
Possible side effects
These side effects are dose-dependent and the risk for them increases (most often linearly but sometimes exponentially) as you increase the dose. Some of the side effects are only relevant to very high doses.
Interaction with Warfarin – Vitamin K can suppress the effects of warfarin to a significant degree.
Risks associated with menadione (Vitamin K3) – This is a synthetic form of vitamin K that has a much higher risk profile. Fortunately, the form is not very popular and it is difficult to come across K3 supplements.
Vitamin K toxicity – This effect is almost exclusive to vitamin K injections and almost impossible to reach through oral supplementation.
Oxidation – Very high doses of vitamin K supplements taken on a basis may increase oxidation in the body. However, there is not a lot of evidence supporting this effect and you certainly do not have to worry about it if you stick to normal doses.
Imbalance in fat-soluble vitamins – Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin K, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones. Fortunately, this is not as big of a problem when it comes to supplementing vitamin K as it is with vitamins A, D, or E.
Who should not take vitamin K?
You should probably avoid taking high doses of the vitamin if you:
already get enough from food
take warfarin (the supplement can suppress the effects of warfarin)
Who will benefit the most?
You should definitely consider taking the vitamin if you:
experience symptoms of vitamin K deficiency
have kidney stones (the vitamin can help pull calcium out of your kidneys)
do not eat a lot of plant foods containing the vitamin
suffer from polycystic ovarian syndrome (PCOS)
suffer from kidney disease (since that significantly increases your need for the vitamin)
are a pregnant or breastfeeding woman (mothers pass high amounts of the vitamin to their unborn babies through the placenta, and to their born babies through breast milk)
take calcium (vitamins K and D help calcium move from places like joints and arteries where it does more harm than good to places where it’s useful, such as bones)
take vitamin D (these two supplements act synergistically in many ways)
are overweight (the more body fat you have, the more vitamin K you need)
Forms of vitamin K
There are 3 main forms of the vitamin usually sold on the market: K1, K2 MK-7, and K2 MK-4. While they are somewhat similar when it comes to their effects, there are some major differences to consider.
Vitamin K1 (Phytonadione or Phylloquinone) – This form is mostly found in plants and is useful primarily for blood clotting.
Vitamin K2 MK-4 (Menatetrenone or Menaquinone-4) – MK-4 naturally occurs in tiny amounts in meat and animal products. This form appears to be the most effective form at reducing the risk of cancer. In order to reduce the risk of cancer, the other forms have to first convert to MK-4. Unfortunately, statins and bisphosphonate drugs used to treat osteoporosis hurt the conversion.
Vitamin K2 MK-7 (Menaquinone-7) – MK-7 is the most effective form at reaching the bones and is thus best for supporting bone health. It also appears to be the best for improving hormonal health and may increase exercise performance, although the evidence for this is rather weak. Most of these effects are a direct result of a hormone called osteocalcin, produced in the bones with the help of vitamin MK-7. This form naturally occurs in some fermented foods, such as natto. It is important to note that those foods contain a full spectrum of vitamin K2 forms, from MK-4 to MK-13. However, MK-7 is the most predominant type in those. This form is also the best one to supplement with. The supplements are either synthetic or natural (derived from fermented soybeans or chickpeas). The natural form is more bioavailable.
Other forms of K2 – MK-4 and MK-7 are not the only types of vitamin K2. There are 10 menaquinones (MKs), ranging from MK-4 to MK-13. However, forms other than MK-4 and MK-7 have not been studied nearly as much and it is uncommon to find them in K2 supplements.
Vitamin K3 (Menadione) – This is a synthetic form of vitamin K that has a much higher risk profile. Fortunately, the form is not very popular and it is difficult to come across K3 supplements.
Signs of vitamin K deficiency
The main symptoms of deficiency include:
excessive bleeding (from the nose, wounds, and internal bleeding)
bruising
vomiting with blood
blood in urine or stool
fatigue
paleness
yellowing of skin and eyes
bone pain
impaired wound healing
irritability
Keep in mind that these signs are just indications of deficiency. The fact that you experience some of them does not necessarily mean that you need more vitamin K. On the other hand, some people may have a deficiency even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance you are not getting enough of the vitamin. The more of these symptoms you experience and the more severe they are, the more likely you are deficient.
How much vitamin K should you take?
The recommended adequate intake is 120 mcg a day for men and 90 mcg for women. However, this recommendation is rather unreliable because it was set in 2001 when there were almost no studies done on vitamin K. It also does not specify the form of the vitamin. That being said, 100+ mcg of either K1 or MK-7 should be more than enough to prevent a deficiency.
If you decide to take the MK-7 form, 100-200 mcg appears to be the best amount to take. The higher end of this range will provide slightly more benefits.
If you take MK-7, there is little to no reason to supplement with vitamin K1. MK-7 is good enough for supporting blood clotting (and, in fact, around 4 times better than the K1 form). There is also a high chance you are already getting enough vitamin K1 from food. If you still want to supplement with K1, around 1,000 mcg a day is a good amount to take.
As far as MK-4 goes, the minimum effective dose starts at 1500 mcg. Doses of up to 45000 mcg have been shown to be safe.
If you are a pregnant or breastfeeding woman, you may need as much as 4 times the amount of vitamin K.
The same applies to people with kidney disease, who may benefit from even more vitamin K (up to 3-4 mg worth of K1 or MK-7). The reason the needs are so high for those with kidney disease is that the kidneys fail to remove enough phosphorus from the body and the elevated phosphorus causes soft tissue calcification. The increased soft tissue calcification requires increased protection from vitamin K.
So to simplify this, it is best for most people to take around 200 mcg of MK-7 a day. If you are a pregnant or breastfeeding woman or suffer from kidney disease, multiply the amount by 4.
If you are deficient in vitamin K and wish to get to the optimal level fast, megadosing is a viable strategy.
As a side note, the recycling of vitamin K requires thiamine, riboflavin, and niacin. Deficiencies of these B vitamins could hurt your vitamin K status and increase your need for this nutrient.
As far as the upper limit goes, taking more than 1,000 mcg of MK-7, 10,000 mcg of K1, or 50,000 mcg of MK-4 regularly usually isn’t necessary and may even cause more harm than good.
Even though oral supplements are extremely safe and have never been shown to cause toxicity, extremely high amounts of vitamin K could lead to oxidative stress and deplete other fat-soluble vitamins (A, D, and E).
Food sources of vitamin K
Vitamin K1 can be found most abundantly in leafy greens. As little as one serving should provide more than enough K1 for the day. You don’t even need to consume these daily since vitamin K stays in your body for a much longer time.
MK-4 can be found in meat and animal products. However, these sources do not provide nearly as much MK-4 as you optimally want to consume. For instance, red meat contains on average 3-4 mcg for 100 calories. To get an adequate intake of K2, you would have to eat around 40,000 calories worth of red meat a day. Organ meats do contain more K2 but still, the amount is by no means significant.
As for vitamin MK-7, by far the richest source is natto with around 300 mcg of MK-7 per oz. This means you would only need to eat around 10 grams of natto to meet the daily requirement. Unfortunately, not many people enjoy the taste of natto and it can be somewhat hard to find unless you live in Japan.
The easiest way to find out how much vitamin K (and other nutrients) you are getting in your diet is with Cronometer.com – the app is free and allows you to track all vitamins, minerals, and more.
Best time to take vitamin K
Since this vitamin is fat-soluble, you need to take it with a source of fat if you wish to maximize the absorption.
More fat will lead to better absorption than less fat in the case of vitamin K so you want to take the vitamin with the meal highest in fat.
If you take vitamin D supplements, take the two vitamins together, preferably also with a meal high in vitamin A. These fat-soluble vitamins increase the absorption of each other.
Whether you take the supplement in the morning or in the evening doesn’t really matter.
You also do not have to take the vitamin every day. There is not a big difference (if any) between taking 100 mcg every day and taking 350 mcg twice a week. The half-life of the vitamin is around 3 days.
Interactions with other supplements
Vitamin D The two vitamins share similar functions in the body and they act synergistically when it comes to improving bone and heart health. Vitamin K also appears to lower the risks associated with too much vitamin D. This is especially true for the K2 form but also applies to vitamin K1.
Vitamin A Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin K, for example, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones. However, you do not need to worry about this if you stick to normal doses of vitamin K.
Vitamin E Getting too much of one of these vitamins could lead to a depletion of the other. This is especially the case if you take a lot of vitamin E. There is a good amount of evidence to support that megadosing vitamin E can lower the blood clotting effect of vitamin K. This is likely by depleting vitamin K levels. This should not be seen as a reason to start supplementing with vitamin E but to include vitamin K into your stack if you already do supplement with vitamin E.
Calcium Vitamin K helps calcium move from places like joints and arteries where it does more harm than good to places where it’s actually useful, such as bones and teeth.
Sesamin Sesamin, a lignan compound found in sesame seeds, appears to inhibit the breakdown of vitamin K, keeping your levels higher for longer. However, the effect appears to be rather small.
Statins Statins can block the conversion of vitamin K1 and MK-7 to MK-4. If you are on stains, you will need to supplement with MK-4 instead of the other forms if you wish to reap the anti-cancer benefits of vitamin K.
Bisphosphonates The same said about statins also applies to bisphosphonates (medications used primarily to treat osteoporosis), such as Fosamax.
Warfarin and other 4-hydroxycoumarins Warfarin, marketed under the name Coumadin and other brand names, prevents blood clots by compromising all of the functions of vitamin K. Unfortunately, this also includes its protection against soft tissue calcification. Consuming more vitamin K can lower or completely diminish the effects of warfarin and other 4-hydroxycoumarins, which are the most commonly prescribed anticoagulants. This effect doesn’t apply to many other anticoagulants, such as Rivaroxaban (Xarelto), Dabigatran (Pradaxa), and Apixaban (Eliquis). These do not interact with vitamin K and are safe to take together with the vitamin.
Where to buy vitamin K
Amazon seems to be the best option for ordering vitamin K supplements in most countries. They offer some very affordable products that are backed by many positive reviews. Also, you can choose from a wide range of brands there without having to spend time searching through other markets on the internet.
One thing you should pay attention to is that some brands display the dosage per serving and not per pill or capsule. Therefore, you may accidentally buy something that is less potent than you intended. Do not fall for this marketing trick.
FAQ
The supplement can be taken daily and does not need to be cycled.
Yes. The vitamin doesn’t impact your sleep in any negative way.
The supplements rarely go bad but they can lose potency over time.
Keep your vitamin K supplements in a cold, dark, and dry place and they will remain just as potent for many years.
It doesn’t directly reduce acne, unfortunately.
Yes. While vitamin K toxicity is extremely rare and almost purely associated with injecting the vitamin, too much vitamin K in the system can cause some problems. Specifically, it can cause an imbalance in fat-soluble vitamin ratios.
Vitamins A, D, E and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin K, for example, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones.
So as a general rule, you want to stay below 1,000 mcg of MK-7, 10,000 mcg of K1, or 50,000 mcg of MK-4 per day.
This depends mainly on how much you take. Higher doses will help you fix the deficiency faster. Even the most severe deficiency could be cured in a few weeks with very high doses.
Put very simply, K1 is a form that comes from many plants and in our bodies, it is responsible for blood clotting. The K2 forms (such as MK-7) can also support blood clotting but they have many additional functions, such as moving calcium to bones and teeth, etc. Fortunately, K1 can convert to K2 to some extent.
Not consuming enough foods rich in vitamin K is the most common reason why one becomes deficient. Warfarin, pregnancy, kidney disease, and a few other things may cause a deficiency by either greatly increasing your need for the vitamin or by greatly reducing its absorption and effects.
You probably need more of the vitamin if you: – have kidney stones (kidney stone could in a way be considered a vitamin K deficiency because there is a very high correlation between vitamin K levels and risk of getting kidney stones; the vitamin can help pull calcium out of your kidneys) – do not eat a lot of plant foods containing the vitamin – suffer from kidney disease (since that significantly increases your need for the vitamin) – are a pregnant or breastfeeding woman (mothers pass high amounts of the vitamin to their unborn babies through the placenta, and to their born babies through breast milk) – take calcium (vitamin K and D help calcium move from places like joints and arteries where it does more harm than good to places where it’s useful, such as bones) – take vitamin D (these two supplements act synergistically in many ways) are overweight (the more body fat you have, the more of the vitamin you need)
K1 and MK-7 supplements are almost always vegan-friendly. As for MK-4, most of the supplements containing this form are produced synthetically and are vegan-friendly. However, since MK-4 comes from animal sources, some of the MK-4 supplements on the market are extracted from animals. Emu oil is one example of this.
No, these are two completely different nutrients. Potassium is a mineral that acts mostly as an electrolyte in the body.
Since these vitamins are fat-soluble, you need to consume dietary fat with them to absorb them properly. Taking these vitamins or consuming them from low-fat food sources without adding extra dietary fat can make some of them up to 10 times less bioavailable. Fortunately, as little as 20 grams of fat should be enough to absorb these vitamins well.
References
Most of the information provided in this guide is based on scientific research that can be found and verified in the PubMed medical library. We excluded from consideration studies that are either confounded or have a high conflict of interest.
Anecdotal evidence (from reports on Reddit, YouTube, and other sources) is also taken into account unless it contradicts scientific research.
