Vitamin K is a fat-soluble vitamin that refers to a family of nutrients with a similar chemical structure.
Vitamin K is found as phylloquinone (K1) and menaquinone (K2) in foods and its synthetic form, menadione (K3).
Depending on which variation of vitamin K we are talking about, it is found in different foods and has various roles within the body. In this article, we’ll dive into vitamin K2.
- History of Vitamin K
- Roles of Vitamin K2 in Your Body
- Medical Uses of Vitamin K2
- Vitamin K2 vs K1
- Vitamin K2-Rich Food Sources
- Bioavailability of Vitamin K2
- Factors Influencing K2 Requirements
- Satiety Response to K2 and Multivariate Analysis
- Antagonists and Synergists of K2
- Can You Get Too Much K2?
- Do We Get Enough Vitamin K2?
- Vegans and Vitamin K2
- How Much K2 Should I Get?
History of Vitamin K
Vitamin K was initially identified in 1929 as a factor that played a crucial role in blood clotting.
When chemists Henrik Dam and Edward Doisy (pictured below) fed chickens low-fat diets to investigate the effects of cholesterol on health, they experienced inexplicable and uncontrolled bleeding. Their symptoms were not relieved by added fat and cholesterol, leaving the researchers to determine what could be causing it.
As they came to find out, this clotting factor was vitamin K. Their discovery would win them the 1943 Nobel Price.
Because vitamin K is fat-soluble, it was deemed that this nutrient—or lack of it because it could not be absorbed—was to blame. Vitamin K is predominantly known for its role in blood clotting, which is how vitamin K got its name; the K in vitamin K stands for the K in the German word Koagulation, or coagulation in English.
In time, researchers discovered that vitamin K was a family of nutrients with similar but variable structures. However, their roles are somewhat similar. This includes phylloquinone (K1) and menaquinone (K2) in foods and the synthetic form menadione (K3). Menadione (K2) was eventually discovered to be composed of several subtypes, named from MK-4 to MK-10.
As we mentioned above, vitamin K2 is several different analogues, now numbered from MK-4 to MK-10. The side chain is the same in each molecule, but the amount of units attached varies. The number of units each contains is outlined by the number in its name. While it doesn’t really influence where you get your K2, it’s a cool little fact to know!
Interestingly, the amount of the different vitamin K subtypes can differ in the same foods depending on where they’re grown or harvested. For example, the amount of MK-4 in US-raised chickens is almost double that raised in the Netherlands and Japan.
Roles of Vitamin K2 in Your Body
Vitamin K1 is most notably active in blood coagulation. Despite its close ties to vitamin K2, the functions of K2 are more varied. We’ve included some of the most important ones below.
- Like vitamin K1, vitamin K2 is a cofactor for an enzyme known as gamma-glutamyl carboxylase. This is a protein that plays a critical role in the blood clotting cascade, and it helps your blood clot.
- Vitamin K2 also plays a substantial role in vitamin K recycling, another critical component of the blood clotting cycle.
- Perhaps K2’s second most important role is its influence on bone quality and calcium storage. While vitamin D helps us absorb calcium and calcium makes up bone, K2 activates osteocalcin, which allows the body to put calcium in bone and away from your muscles, joints, or arteries. Vitamin K1 had little impact when studied.
- K2 is also helpful for calcium regulation in other parts of the body; the kidneys utilise K2 to remove excess calcium, prevent kidney stones and prevent poor renal artery function and calcification. Additionally, it has been shown to increase GFR.
- New research has shown that vitamin K2 has a role as an antioxidant and protects the body from lipid peroxidation. This can be beneficial, as it can prevent neuro cells from oxidative stress and help to rescue mitochondrial imbalances.
- Proteins that prevent and protect against the development of vascular calcifications (i.e., arterial plaques) rely on vitamin K2, and studies have shown a regression in arterial stiffening with regular K2 consumption.
- In addition to calcium storage, it has been shown that osteocalcin also helps promote pancreatic beta-cell proliferation. These cells produce insulin. K2 has been positively associated with blood glucose control and insulin production.
- Because of its relationship with osteocalcin, K2 has been linked to fewer adipocytes. Studies have linked greater K2 intakes to lower body weight, waist circumference, body composition, visceral fat, and Type-2 Diabetes.
- More recently, vitamin K2 has been shown to regulate T-cell production and have an immunomodulatory role. K1 was not shown to have the same effect.
- K2 has been linked to the regeneration of cells within the liver, which can be helpful in certain carcinomas stemming from cirrhosis. However, this is still under investigation.
- Vitamin K2 has been shown to activate proteins that regulate inflammation, cell division, and soft tissue mineralisation.
- Adequate vitamin K levels have been linked to better reproductive health. Studies have specifically shown a connection between vitamin K and healthy sperm maturation.
- K2 has a role in brain health, as myelinated regions of the brain seem to require high amounts of K2. Low levels of K2 are linked to neurological spasms and optic nerve lesions in people with Multiple Sclerosis (MS), which may suggest that deficiency plays a role in this illness. However, this is still being researched.
- Low levels of vitamin K2 are also linked to neurodegenerative conditions like Alzheimer’s. This could be because of its role as an antioxidant or because it plays a part in insulin sensitivity.
- K2 has been shown to restore mitochondrial function, which is often damaged in chronic diseases like diabetes, autoimmunity, cancer, autism, and heart disease.
- Interestingly, your body efficiently recycles vitamin K.
Medical Uses of Vitamin K2
Medical uses for vitamin K2 have increased as research has continued to develop. To date, vitamin K2 has been used in a medical setting for:
- Regulating bone-related diseases, like osteoporosis, osteopenia, and osteomalacia;
- Improving cardiovascular disease-related symptoms, like arterial stiffening, arterial plaques, and inflammation;
- Chronic kidney disease and improving the glomerular filtration rate (GFR);
- Prevention of certain cancers;
- Regulation of the immune system;
- Improving insulin release;
- Remyelination of nerves in conditions like Multiple Sclerosis; and
- Liver regeneration.
Vitamin K2 vs K1
Vitamin K is an essential nutrient required for human health; however, it appears in several different forms, namely K1 (phylloquinone) and K2 (menaquinone).
Vitamin K1 is primarily found in green and leafy things, whereas vitamin K2 is predominantly found in animal foods or fermented foods. Similar to B12, it is synthesised by bacteria.
A lot of the focus today is on K1, not K2; all nutrition databases to date only have consistent data on the vitamin K1 content of food, and the recommended daily intakes are based on vitamin K1. K1 and K2 differ in tissue distribution, bioavailability, and absorption, which makes it more challenging to come up with accurate data than vitamin K1.
Because our knowledge of human nutrition is relatively new and the science of nutrition and dietetics is relatively young, our knowledge of which form may be the best continues to change. In the case of vitamin K2, newer research shows that K2 may be absorbed better.
While the nutrients have similar ring structures, they have different side chains. However, we know that the body can convert K1 to more active K2 in the GI tract or the liver.
In terms of effectiveness, K2 seems to be more than three times more effective than K1 in activating proteins for skeletal metabolism. Research has shown that the influence of K1 and K2 on cardiovascular disease is not the same; K2 is effective, whereas K1 is not. Additionally, as you can see from the ‘roles’ section, K2 plays a part in blood clotting like K1, but it also influences liver function and regeneration, blood glucose regulation, pancreas health, protecting the body from oxidative damage, nervous system health, and bone integrity.
While it could be easy to say that one form of vitamin K is more important than the other, we feel it is important to highlight that focusing on a nutrient-dense omnivorous diet should provide you with more than enough of each. By focusing on foods that pack more of all the nutrients—rather than foods or supplements that contain a single macronutrient, vitamin, mineral, amino acid, or essential fatty acid—you will get the complete profile of ALL the nutrients you need (and then some).
Vitamin K2-Rich Food Sources
Foods that are rich in vitamin K2 include:
- hard cheese
- cheese curds
- liver of any sort (i.e., duck, goose, chicken, veal, beef, lamb, pork)
- egg yolks
- egg yolk
- emu oil
- other dairy products
Note: bacteria create vitamin K2 through fermentation. Hence, unfermented plant foods are not good sources of vitamin K2.
Bioavailability of Vitamin K2
Because vitamin K is a fat-soluble nutrient, we must consume it with a fat source to absorb it properly. Fortunately, most high-K2 foods like meat, poultry, and dairy contain ample amounts of fat, meaning you don’t have to worry much.
If you’re looking to up your K game, it’s best to add some butter to your greens! Not only does it taste good, but it’s a sure way to provide yourself with some K1 and K2.
In short, multiple studies have shown that various analogues of K2 are absorbed much better than K1. Research indicates that the MK-7 of K2 is absorbed best of any other form of vitamin K; it has been shown to be around tenfold higher than K1. MK-4, the variation of K2 found amply in animal protein, comes in second, and is still higher than K1.
Factors Influencing K2 Requirements
Because K2 plays a role in calcium storage, insulin release, neurological health, and blood clotting, someone with a condition associated with these processes may require more K2. For example, you may benefit from more K2 in your diet if you experience any of the following:
- Cardiovascular disease,
- Type-2 Diabetes,
- Sensitive or decaying teeth,
- Immune dysfunction,
- Liver disease,
- Certain types of cancer,
- Breastfeeding, or
- Multiple sclerosis,
Similarly, someone who has taken K2-depleting drugs like blood thinners that work by inhibiting vitamin K recycling (i.e., Warfarin and Coumadin) may have an increased demand for K2. Once again, we want to highlight that taking more K2 while on these specific drugs may counter the effects of the drug and render them useless. Hence, it’s best to talk to your MD about how to satisfy your vitamin K demands.
Satiety Response to K2 and Multivariate Analysis
Most databases measure vitamin K1 in foods, not vitamin K2. Because most nutrition databases do not have much K2 information, we don’t have reliable data to run our satiety analysis for vitamin K2.
However, we know that many foods containing K2 tend to align with greater satiety. Aside from protein leverage, our analysis has shown a sort of nutrient leverage at play, meaning we will eat more energy until we get our fix of nutrients.
Antagonists and Synergists of K2
Nutrients tend to have synergistic and antagonistic relationships with one another, sometimes simultaneously. In synergy, nutrients require one another to work and can increase the retention of others. In antagonism, nutrients can deplete one another.
The greatest synergists of vitamin K are vitamins A, D, and calcium, but it also works alongside vitamins B3, B6, C, and manganese. These nutrients can increase the effects of vitamin K and compound its retention depending on their roles.
The greatest antagonists are vitamins A and E; vitamin E in high doses is known for its blood-thinning effect. While seeing the same nutrient as a synergist and antagonist may be confusing, the critical takeaway is not to overconsume too much of one nutrient! This is typically how imbalances occur.
For more on this, check out our Micros Masterclass and Nutrient Balance Ratios: Do They Matter, and How Can I Manage Them?
Aside from essential nutrients, the blood-thinning drug Warfarin may be the greatest antagonist of vitamin K. Warfarin inhibits the recycling of vitamin K, meaning it can deplete your levels of this nutrient over time.
If you are taking Warfarin—or another blood thinner like Coumarin that works via vitamin K antagonist—you should not mean you should compensate by consuming lots of natto and kraut! K2 in foods can even counter the effects of these drugs, so it’s best to talk to your MD about looking after your nutrient levels.
Can You Get Too Much K2?
As mentioned above, the body does not store vitamin K2 despite being a fat-soluble nutrient. For this reason, there haven’t been any reports of vitamin K2 toxicity from supplements or food, despite one case of someone with multiple pre-existing health conditions.
While vitamin K2 and K1 have no known side effects from toxicity to be weary of, the same cannot be said for their synthetic analogue, menadione (K3). This form of K3 is administered to most newborns as the vitamin K shot, and there have been reports of vitamin K3 toxicity.
It’s worth mentioning that if you’re taking a blood-thinning drug like Warfarin that disrupts the blood clotting cascade, taking K2 won’t result in toxicity, but it will counter the effects of this medication. This will occur regardless of whether you take it as a supplement or eat it in food.
Do We Get Enough Vitamin K2?
To date, it’s hard to say if we’re getting adequate K2. Because we have sparse data for this vitamin, we can’t make a data-driven conclusion. That said, we can look at associations and develop some theories.
Greater intakes of vitamin K1, the less-active relative of vitamin K2, is inversely correlated with satiety (i.e., we eat more when we consume less, and vice versa). So, it’s likely that foods with more Vitamin K2 per calorie would also align with greater satiety.
For more on vitamin K1, check out High-Vitamin K1 Foods and Meals.
Vitamin K2 is found in some fermented plant foods, but it’s more amply available in animal foods like egg yolks, dairy, butter, poultry, seafood, and other meats. Since the release of the 1977 Dietary Goals for Americans, we have been consuming far less of these foods out of fear of cholesterol and saturated fat.
While it may seem surprising, our multivariate satiety analysis has shown that these decreases in saturated fat and cholesterol consumption—and likely vitamin K2—have correlated with an increase in obesity.
As a result of avoiding these ‘danger foods’, we have also consumed less vitamin A.
Based on these trends and this inference, we likely consume far less vitamin K2 than we did 50 years ago. For more on prominent dietary trends, visit How the Biggest Trends in Nutrition Influence How We Currently Eat.
Additionally, we know that our vitamin K2 intake from foods corresponds to only 25 and 5% of our total vitamin K intake. Although vitamin K1 is a precursor to vitamin K2, it isn’t the most efficient process, and much of the population struggles to consume adequate K1, which is abundant in green and leafy vegetables. We likely do not consume adequate K2 on a standard western diet alone, particularly from ultra-processed foods.
Vegans and Vitamin K2
Vegans and certain types of vegetarians (i.e., those who do not consume dairy) cannot get their K2 from animal foods like cheese, yogurt, meat, and dairy. However, they can consume lots of sauerkraut, kimchi, and natto.
If they are consuming a whole food, plant-based diet, they may get enough K1 from greens, fruits, and vegetables to account for some of their K2 demand. Coupled with several servings of fermented foods, this may provide them with all the K2 they need. On the other hand, lactovegetarians who consume dairy have ample foods to choose from to get their K2.
For more on a vegan diet, check out Is A Vegan Diet Healthy? Why Chasing Nutrients Might Be More Important.
How Much K2 Should I Get?
Although vitamin K is a fat-soluble vitamin that the body can recycle, it only holds onto small amounts of this nutrient. As a result, it only holds onto small amounts of this nutrient. As a result, vitamin K stores can be depleted rather quickly if they are not replaced via diet.
To date, all the research on our requirements for vitamin K is on vitamin K1, meaning we don’t know exactly how much we should consume for optimal health—or even to evade diseases associated with deficiency.
Interestingly, research in 1997 showed that the US dietary vitamin K intake did not provide adequate amounts of the nutrient to execute all of its critical functions, like catalysing osteocalcin.
As we mentioned, all the nutrient databases measure the quantity of vitamin K1 in food, and few measure the K2 content. Nonetheless, experts like Chris Masterjohn recommend consuming at least 100 to 300 micrograms of K2 daily.