Vitamin K is a crucial nutrient for calcium metabolism, bone health, blood clotting, heart health, and more. K2 is the form present in animal and fermented foods. As a supplement, vitamin K2 may help with osteoporosis, heart disease, inflammation, and more. Read on to learn the benefits, side effects and food sources of vitamin K2.
Vitamin K2, also known as menaquinone, is involved in blood clotting, bone health, and the regulation of some cellular functions in the human body .
Vitamin K2 is also important for regulation of cell growth, and maintenance of the arterial wall .
There’s two main types of Vitamin K2: MK-4 and MK-7 .
Vitamin K2 in the form of MK-7 has a much longer half-life than the synthetic K1, which means it stays in your system for longer .
Vitamin K1 comes from plant sources, while animal foods and some fermented products contain K2. Humans can partly convert vitamin K1 to K2 and produce K2 with the help of probiotics .
- Promotes strong bones and teeth.
- Improves Cognitive performance.
- Decreases inflammation and helps some autoimmune conditions.
- Reduces risk for heart disease and improves circulation.
- People on blood thinners should limit their K2 intake to amounts typically found in the diet.
Vitamin K is a cofactor for γ-glutamyl carboxylase, which enables carboxylation of glutamic acid to γ-carboxyglutamic acid.
Vitamin K2 helps transport electrons in the mitochondria, similar to ubiquinone, which helps boost mitochondrial function and create energy.
However, in mice liver cells, it wasn’t able to replace all the functions ubiquinone .
In a fly model of Parkinson’s, K2 was able to help by improving the mitochondria.
Vitamin K2 is the principal form of vitamin K that the brain uses.
Vitamin K2 (MK-4) was found to represent greater than 98% of total vitamin K in the brain, irrespective of age .
Vitamin K’s effects are hypothesized as a result of “sphingolipid metabolism” .
Vitamin K2 (MK-4) positively correlates with sulfatides and sphingomyelin, two brain-protective components .
Important: this post will focus specifically on the benefits of vitamin K2. Another form of this vitamin, K1 or phylloquinone, is used for:
- Hemorrhagic disease in newborns 
- Hypoprothrombinemia (impaired blood clotting) 
- Vitamin K-dependent clotting factors deficiency (VKCFD) 
- Warfarin and other anticoagulants toxicity [14, 15]
Osteocalcin needs vitamin K2 to become fully activated and bind calcium .
Vitamin K2 deficiency can lead to arterial defects and osteoporosis as calcium gets deposited in the blood vessels instead of the bones. Low levels of Vitamin K were alos linked to increased inflammation, fractures, and bone pain [2, 19].
According to a review of eight smaller Japanese clinical trials, vitamin K2 supplementation increases bone mineral density (BMD) and lowers the incidence of fractures in postmenopausal women with osteoporosis .
However, a much larger trial of over 4,000 older Japanese women found only minor benefits of K2 supplementation. It reduced the risk of spine fraction only in women with advanced osteoporosis .
A recent update warned about low-quality trials in older reviews with positive results and suggested further investigation. Another limitation is that all studies were done on Japanese women .
There’s an association between higher intake of vitamin K2 and lower risk of heart disease. For every 10 micrograms of K2 consumed per day, the incidence of heart disease was reduced by 9% in a comprehensive trial of over 16,000 women .
In a study of 4,800 participants, people with the highest intake of Vitamin K2 were 52% less likely to develop calcification of the arteries; they had a 57% lower chance of dying from heart disease, over a 7-10 year period .
According to a review of 27 clinical trials and over 12,000 participants, vitamin K supplementation significantly improves the calcification of blood vessels but doesn’t improve their stiffness. Additionally, some studies used vitamin K1 .
No valid clinical evidence supports the use of vitamin K2 for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.
A study of 380 women had similar results but failed to confirm the benefits of supplementation .
In 158 women with rheumatoid arthritis, a daily dose of 45mg Vitamin K2 reduced inflammation and disease activity .
More research is needed to evaluate the beneficial effects of K2 supplementation on inflammatory and autoimmune conditions.
Higher vitamin K2 (but not K1) intake was linked to 63% lower rates of advanced prostate cancer in a trial of 268 patients .
An increase in dietary intake of vitamin K (both K1 and K2) was associated with two times lower cancer mortality in over 7,000 study participants .
According to a review of 6 clinical trials and 930 patients, vitamin K2 supplementation may improve overall survival and reduce recurrence of liver cancer after surgery. However, the beneficial effects we seen only after 2- and 3-year follow-up .
Larger, well-designed trials are needed to investigate the potential anticancer effects of vitamin K dietary intake and supplementation. At this point, K2 supplements can’t be recommended for cancer treatment or prevention.
An increase in dietary intake of vitamin K was associated with a reduced risk of dying from all causes in a Mediterranean population at high cardiovascular disease (n=7216). Further research is warranted .
Some hypothesize that vitamin K can help with varicose veins. However, the study most people are citing doesn’t say vitamin K2 helps.
On the other hand, MGP is a strong inhibitor of vascular calcification when it’s carboxylated .
Vitamin K2, but not K1, is needed to carboxylate MGP, which helps avoid calcification in the arteries .
Bottom line: there’s sufficient evidence that K2 will help or hurt varicose veins.
This list does not cover all possible side effects. Contact your doctor or pharmacist if you notice any other side effects. In the US, you may report side effects to the FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada, you may report side effects to Health Canada at 1-866-234-2345.
Vitamin K2 supplements are generally safe, well tolerated, and suitable for long term consumption. They may cause only minor digestive side effects in some patients .
Nutrient-drug interactions can be dangerous and, in rare cases, even life-threatening. Always consult your doctor before supplementing and let them know about all drugs and supplements you are using or considering.
All forms of vitamin K supplements significantly reduce the effectiveness of Warfarin and other blood-thinning medications, leading to potentially fatal complications. Patients on blood thinners should carefully monitor their vitamin K dietary intake, and they must not use vitamin K supplements .
Broad-spectrum antibiotics can contribute to K2 deficiency as a result of killing bacteria that produce K2 .
Other risk groups include:
- Liver disease patients .
- People with inflammatory bowel disease or cystic fibrosis [43, 44].
- Babies who are exclusively breastfed .
K2 is generally higher in the fat of animals, especially those that are grass fed. K1 is found in plants.
Dietary intake of vitamin K2 accounts for up to 25% of total vitamin K intake .
Humans can partly convert vitamin K1 to K2 in the body, but the conversion process is inefficient.
Here are the levels of K2 from animals in the US that aren’t grass fed. Japan has higher values for all of these foods, while the Netherlands is mixed.
- Ghee from grass-fed animals
- Chicken: 13.6-31.6 micrograms/100g 
- Pork: 0.2-9.9 micrograms/100g 
- Beef: 1.1-9.3 micrograms/100g 
- Egg yolks: 15.5 micrograms/100g 
- Salami: 9 micrograms/100g 
- Milk: 0.8-1.0 
- Cheese: 4.7-10.2 micrograms/100g 
- Sauer Kraut: 0.4 micrograms/100g 
- Natto (fermented soybeans): 939-998 micrograms/100g of MK7 .
Other general categories of food:
- Fermented foods 
- Liver and other organs 
- Dairy products from grass-fed animals (cheese, curds, yogurt, milk) [46, 51, 48].
Menaquinones produced by bacterial species commonly used in industrial food fermentations :
|Lactococcus lactis subsp. lactis||Cheese, buttermilk, sour cream, cottage cheese, cream cheese, kefir||√||√||√||√√|
|Lactococcus lactis subsp. cremoris||Cheese, buttermilk, sour cream, cottage cheese, cream cheese, kefir||√||√||√√|
|Staphylococcus xylosus||Dairy, sausage||√||√√||√|
|Staphylococcus equorum||Dairy, meat||√||√√||√|
|Bacillus subtilis “natto”||Natto||√√|