The Slightly Disturbing Reason why Chicken Thighs are High in Vitamin K2

The Slightly Disturbing Reason why Chicken Thighs are High in Vitamin K2

Vitamin K2 content of poultry meat

Chicken is not naturally rich in Vitamin K2.

If you want foods rich in K2, reach for Japanese Natto (gooey, stretchy fermented soybeans), goose liver, European hard cheeses, sauerkraut, and liver. Not exactly drool-worthy stuff. 

But if you look at lists of foods rich in Vitamin K2, you often see chicken dark meat or even pork sausage listed. This is great because we (Americans) are far more likely to eat chicken than goose liver or Natto. 

So, if chicken is not naturally rich in Vitamin K2, how did the K2 get there?  

Animal feed. That's how. 

Vitamin K2 in Animal Feed

Vitamin K2 is an important nutrient for animals, not just humans.

There are many forms of K2 for animals and only a couple can or should be used in animal feed. Several of these synthetic Vitamin K2 forms are not approved for use in the US.

There are three types of Vitamin K: K1, K2, and K3. 

K1 and K2 are naturally occurring substances found in foods. K3 is a synthetic form.

  • Vitamin K1, sometimes called phytonadione or phylloquinone, is the kind of Vitamin K that is found in plants, especially leafy greens.
  • Vitamin K2, or menaquinone, is the kind we are interested in. There are many different types of K2 such as MK-4 and MK-7. This is usually found in fermented foods and organ meats. 
  • Vitamin K3, also known as menadione, is a synthetic form of Vitamin K. It is converted to Vitamin K2 in the guts of animals. Chickens and pigs are very good at converting synthetic K3 to human-friendly K2. K3 is not permitted for human use and there are some concerns

Chickens and turkeys have short digestive tracts and a rapid rate of food passage. This makes them more prone to Vitamin K deficiency than other animals. If not addressed, it can be a serious problem in raising chickens.  

Cows don't have this problem because they have elaborate guts with fermentation chambers. This microbial fermentation of grasses produces a good amount of Vitamin K2, especially MK-4 form of K2. This is why grass-fed beef liver is a good source of Vitamin K2.

Back to chickens...

The forms of synthetic Vitamin K used in poultry farming are: 

  • Menadione dimethylpyrimidinol bisulfite
  • Menadione sodium bisulfite
  • Menadione nicotinamide bisulfite

None of these K3 forms are allowed in human nutrition or supplements. 

They have, however, been used as part of animal feeds for over 60 years and are generally believed to be relatively safe due to their long history of use. (Source: American Feed Control Official)

These ingredients are also added to swine feed. 

Is synthetic Vitamin K3 safe for humans?

No. It's not safe for humans.

Fortunately, K3 is banned for human use. 

Vitamin K3 or Menadione can interfere with Glutathione, our body's main antioxidant and detox agent. Consuming Vitamin K3 can cause excessive oxidative damage to cell membranes because it interferes with Glutathione doing its job. 

Children given Vitamin K3 injections to treat Vitamin K deficiency were noted to have liver toxicity, anemia, and jaundice

It's fair to assume (but we don't know for sure) that K3 does the same harm to poultry, swine and possibly to Fido and Fifi as well.

Learning this may be somewhat upsetting as you are consuming the byproducts of synthetic Vitamin K3. Since birds and pigs convert K3 to human-friendly K2, there is no need for alarm.

If you eat chicken dark meat or pork, you are not consuming Vitamin K3, because K3 is quickly converted to a safe form of K2. 

It is important to note that Vitamin K1 or K2 do not show these negative side effects, even at high doses...barring, allergies, of course.

Our grandparents ate liver and fermented foods regularly. This could have kept them from serious K2 deficiency. We're not as lucky. So, artificially boosted K2 in chicken dark meat and pork sausages may be keeping millions of us from becoming severely deficient in Vitamin K2. 

This may be a blessing in disguise. 

How much Vitamin K2 is in chicken and pork? 

Well, the amount in the meat depends on how much synthetic Menadione (K3) was fed to them. You can feed them 1000X more than what they need before they exhibit negative side effects. Of course, being a for-profit industry, the poultry industry will feed the chickens just enough K3 to prevent acute deficiency, and not an ounce more. 

Amount of Vitamin K2 (micrograms or mcg) in four ounces:

  • Chicken dark meat: 60 mcg 
  • Porkchop with bone: 75 mcg
  • Chicken breast meat: 9 mcg
  • Chicken tenders: 6 mcg
  • Chicken sandwich: 4 mcg

Chicken dark meat and pork chop have over 60 mcg. Hey, that's not bad!

It is important to remember that K2 is stored in the dark meat, not the white meat. 

A chicken sandwich has just a fairy dusting with 4 micrograms. So you'd have to eat 25 chicken sandwiches a day to get a solid dose of Vitamin K2. 

Unfortunately, most Americans instinctively avoid dark meat because it is considered fatty. 

Vitamin K2 is fat-soluble and is concentrated in fatty meats. 

Chicken dark meat is very high in Omega-6 fatty acids, which may offset some of the beneficial effects of healthy Omega-3 fats. We consume far more Omega-6 than we need and there may be some negative health effects to this. 

So you balance the good with the bad - chicken dark meat is where the Vitamin K2 is, but it also contains a large amount of Omega-6 fats.


  • Vitamin K2 in chicken and pork products are a result of feeding them synthetic K3 Menadione compounds.
  • Synthetic Vitamin K3 is banned for human use.
  • Chicken and pigs convert synthetic K3 to human-friendly K2.
  • K2 is concentrated in chicken dark meat, not the white, breast meat.
  • Without this animal feed addition, many of us might be even more deficient in Vitamin K2 than we already are. 


Friedrich, W. 1988. Vitamins. Walter de Gruyter, Inc. McDowell, L. R. Vitamins in Animal and Human Nutrition. 2000. 2nd Ed. Iowa State Univ. Press, Ames.

National Research Council. Vitamin Tolerance of Animals. 1987. National Academy Press. Washington, DC.

Shearer, M. J. Vitamin K1. Lancet. 1995. 345(8944): 229-234.

Food and Nutrition Board, Institute of Medicine. Vitamin K. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, D.C.: National Academy Press; 2001:162-196. 

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