Vitamin K1 vs. K2: Expert’s Guide on This Essential Nutrient

In the most basic terms, vitamin K is necessary to support clean arteries and strong bones. 

What really is vitamin K? 

Vitamin K is actually several vitamins – K1, K2, and K3. Vitamins K1 and K2 are used in nutritional supplements.  

Vitamin K1, also known as phylloquinone, is widely found in plants. 

Vitamin K2, also known as menaquinone, is found more often in animal products; technically it is a group of several different molecules that are identified based on the length of their side chains – from MK-2 to MK-14. The two forms of vitamin K2 most often used in nutritional supplements are MK-4 and MK-7. 

Vitamin K3 is synthetic and has primarily been used in clinical investigations in cancer research. 

Who should be taking vitamin K? 

Although it is common to draw a distinction between vitamin K1 vs. K2, their effects on the body overlap extensively, and we’ll use the term vitamin K below to refer to both forms. 

Vitamin K is so essential for bone and vascular health it’s hard to identify an individual who would not benefit from its supplementation. 

You might especially benefit from vitamin K supplementation if: 

• You regularly take an antacid 

• You take a statin for cholesterol management (recent research suggests statins can cause a vitamin K deficiency¹) 
• You have a GI problem that causes fat malabsorption because vitamin K is fat-soluble 
• You have been taking an antibiotic, because, in addition to diet or supplement sources, vitamin K2 is produced by gut bacteria 
• You take a weight loss medication that inhibits fat absorption  
• You supplement with vitamin D or calcium, because vitamin K helps direct calcium to the bones and away from soft tissues like arteries where you don’t want it 

• You are a peri- or postmenopausal woman – a time when bone and cardiovascular health can suffer 
• You are pregnant or trying to conceive (be sure vitamin K is in your prenatal vitamin) 
• You are concerned about your bone or cardiovascular health 

How much vitamin K is needed? 

It was previously believed that the body needed only a tiny amount of vitamin K because that was all that was needed for blood coagulation.  

However, unlike its need in activating blood clotting proteins, higher levels of vitamin K are essential for the activation of other proteins, such as osteocalcin for bone health. 

Thus, it appears that a higher level of vitamin K is needed to support bone and vascular health compared to the level needed for blood clotting. 

But the ideal vitamin K dosage for adults is not a one-size-fits-all answer because it depends on the form of vitamin K. Taking both vitamin K1 and vitamin K2 is the best way to ensure adequacy. 

What about dietary sources of vitamin K? 

Dietary sources of vitamin K1 vs. K2 differ.  

Vitamin K1 is found in its highest concentration in green leafy vegetables, although it might not be very well absorbed from these sources. For example, one study found 6-times greater absorption of vitamin K1 from a nutritional supplement than from green vegetables like spinach, broccoli, and romaine lettuce.³ 

Vitamin K2 in the MK-4 form is found in butter, meat, eggs, and cheeses – particularly aged cheese. Gouda and brie are reported to be the cheeses with the highest amount of the MK-4 form. 

Vitamin K2 in the MK-7 form is found in fermented foods, most notably natto, a traditional Japanese food made from fermented soybeans.  

The amounts of vitamin K2 in animal products and fermented vegetables vary widely. For example, some reports suggest dairy products from grass-fed cows and eggs from free-range chickens have higher amounts of vitamin K2 than grain-fed cows and chickens. Vitamin K2 is also produced by gut bacteria. 

Because of the unreliability of dietary vitamin K content and its absorption, a nutritional supplement should be considered. 

How is vitamin K absorbed and how long does vitamin K stay in your system? 

Vitamin K is absorbed in the small intestine. Because it’s a fat-soluble vitamin, its absorption requires bile and pancreatic enzymes. Thus, taking a vitamin K supplement along with some fat in a meal is the best way to assure absorption. 

Regarding, how long does vitamin K stay in your system – it depends on the form of vitamin K – vitamin K1 vs. K2. Unlike other fat-soluble vitamins, vitamin K1 is rapidly metabolized and excreted from the body within several hours. On the other hand, vitamin K2, because its chemical structure is comprised of long side chains, can take several days to be fully metabolized. 

Can too much vitamin K cause blood clots? 

Generally, the answer is no. However, if you have a concern, then consult with your health-care professional, particularly if you have a blood clotting issue or are taking an anticoagulant medication. 

If you supplement vitamin D, don’t forget the K. 

Just like salt goes with pepper, and wine goes with chocolate, and magnesium goes with calcium, vitamin K goes with vitamin D. Vitamin K supplementation should always be paired with supplemental vitamin D when possible. 

Although vitamin D increases the absorption of calcium to provide important support for bone health, vitamin K directs that absorbed calcium to the bones and not to the soft tissues, such as the blood vessels and the kidneys.