There is increasing interest in the menaquinones, the forms of vitamin K2 that are produced in animal tissues and as a result of bacterial fermentation. What information there currently is in the scientific literature about its content in foods appears to be rather scattered in journals that few people have access to so I thought I would have an attempt to present some of the most relevant information together here. What I hope this will do is both show how limited the testing so far has been, the variation among similar foods, and the range of sub-types of vitamin K2 to be found in our foods.
Vitamin K is an essential nutrient for the human body however rather than being a single compound it is composed of a group of structurally related compounds. These compounds all include the same active quinine ring molecule at their end giving them their vitamin K activity. Where they differ is in their side chains, with vitamin K1 having a tail of four phytyl groups, while the tails of the vitamin K2 sub-types are formed of a varying number of isoprenoid groups.
Vitamin K1 (Phylloquinone) is always of plant origin and is the form of vitamin K that has been known longest. It’s occurrence in plant foods can be found detailed in food nutrient databases. Vitamin K2 (Menaquinones) is less well known and only occurs in foods of animal origin or foods altered by bacterial fermentation. Menaquinone-4 (mk-4), the sub-type produced by animal tissues and menaquinone-7 (mk-7), found in the fermented soya bean food natto, are the best studied but a number of other forms are found in fermented dairy products like cheese.
Liver is often seen suggested as a source of vitamin K2 and beef liver in particular has been recommended as a good dietary source. From the tables below it seems that while the beef liver tested contains mk-4, it is not a particularly good source. However, most studies have not tested for long-chain menaquinones, mk-6 to mk-13, which are produced by the bacterial fermentation in the stomachs of cattle and provide them with a readily absorbable source of vitamin K2. When absorbed from the gut these reach the liver first where they appear to remain. This can be seen as very little long chain menaquinones were detected in any of the other meat or organs of cattle. The only small study that has tested for these found quite high levels of menaquinones 11, 12, and 13. I would like to see this confirmed but it does suggest that mk-4 is not the whole story in beef liver. Unfortunately, the total amount of vitamin K2 and the various menaquinones in beef liver is uncertain, as only lone small study has measured these.
Poultry products, including liver, are generally a good source of vitamin K2 in the form of menaquinones-4. Other forms of vitamin K2 are not found in chicken as chickens have a limited capacity for bacterial production of menaquinones in their gut, relying instead on vitamin K in their diet. In their natural diet this would probably be provided by phylloquinone in the leaves of plants they eat which is converted into menaquinone-4 by the chicken. However, the feed of poultry is instead usually supplemented with plenty of menadione, a synthetic form of vitamin K (K3), that is readily converted in to menaquinone-4, resulting in high levels of mk-4 in all parts of the chicken. The menadione is added because chickens are vulnerable to vitamin K deficiencies, particularly when they are young, and the addition of menadione reduces the risk of this deficiency on commercial chicken farms. This leads me to suspect that the high levels of menaquinone-4 reported in the liver, meat and egg yolks of chickens tested so far, which are all most likely to have come from commercially reared chickens, may be due to their supplemented feed. It is possible that chickens kept under conditions that are more natural for the chicken will have lower levels of menaquinones-4 in their meat and eggs. My understanding is that due to the large amounts of bacteria in the guts of ruminants they do not usually require supplemental forms of vitamin K in their diets.
Of all the animal foods foie gras, the fattened liver of force fed geese, stands out as the richest source of vitamin K2 in the form of menaquinone-4. It seems uncertain as to why this liver and their flesh contain such high amounts. Geese will graze on green plants to a greater degree than chickens, if given the chance, and perhaps they are just very good at converting phylloquinone to menaquinone-4. However, during the production of foie gras geese are fed a diet high in corn that is not a good source of vitamin K. I am uncertain as to whether their diets are also supplemented with menadione.
The vitamin K in dairy products is mostly in the form of menaquinone-4 produced in the tissues of the cow from other forms of the vitamin in their diets for from their intestinal bacteria. Phylloquinone (K1) can also be seen in small amounts and must originate from the diet of the cows. As menaquinone-4 is fat soluble it is concentrated in dairy products with higher fat contents with butter containing the most.
The various types of natto tested contain the highest content of vitamin K2 of any food in the form of menaquinone-7. Sauerkraut was also tested by a single study in the Netherlands and showed rather small amounts of a variety of menaquinones, although how traditional the methods of manufacture were is unknown.
The menaquinones found in cheese are mostly mk-6 to mk-10 which are the menaquinones produced by the bacteria used in the production of cheeses. Small amounts of phylloquinone and menaquinones-4 are also found which originate from the milk used. The amount and mixture of menaquinones in fermented dairy products seems to vary quite a lot between different products and within the same type of product. Cheeses produced with propionibacteria, such as Jarlsberg, Emmental, and Gouda have been shown to contain some of the highest amounts in the form of menaquinone-9. However, the results here show that other types of cheese, including soft cheeses and blue cheese can equally contain high amounts of various menaquinones. The nutritional effect of this form of vitamin K on human health have so far received little attention.
A surprising finding is the menaquinone-9 content of mesophillic fermented milks from various countries. Unhelpfully the study in question does not detail what these products were though mesophilic refers to the lower temperature of the fermentation and so implies that these were milk products such as kefir.
Elder SJ, Haytowitz DB, Howe J, Peterson JW, Booth SL. (2006) Vitamin k contents of meat, dairy, and fast food in the U.S. diet. Journal of Agriculture and Food Chemistry. 25;54(2):463-7. (Pubmed).
“The purpose of this study was to determine the contents of three forms of vitamin K [phylloquinone, dihydrophylloquinone, and menaquinone-4 (MK-4)] in representative samples (including different samples within the same food category) of meat (n = 128), dairy and eggs (n = 24), and fast foods (n = 169) common to the U.S. diet. The findings of our analysis indicate that no single food item in these categories is a rich dietary source of any one form of vitamin K. However, these foods are often consumed in large quantities; hence, they may be of importance in overall contribution to total vitamin K intake. The presence of MK-4 in meat, eggs, and dairy foods could be important as physiologic functions unique to MK-4 are identified.“
Hirauchi K, Sakano T, Notsumoto S, Nagaoka T, Morimoto A, Fujimoto K, Masuda S, Suzuki Y. (1989) Measurement of K vitamins in animal tissues by high-performance liquid chromatography with fluorimetric detection. Journal of Chromatography. 29;497:131-7. (Pubmed).
“A highly sensitive method for measuring endogenous phylloquinone and menaquinones in animal tissues was developed, based on high-performance liquid chromatography with coulometric reduction and fluorimetric detection, following extraction from tissue homogenate and purification on a Sep-Pak silica cartridge followed by thin-layer chromatography. The detection limits of phylloquinone, menaquinone-4, -6, -10 and -13 were 40, 40, 50, 70 and 80 pg/g in rat liver, respectively.”
Hojo K, Watanabe R, Mori T, Taketomo N. (2007) Quantitative measurement of tetrahydromenaquinone-9 in cheese fermented by propionibacteria. Journal of Dairy Science. 90(9):4078-83. (Pubmed).
“Propionibacteria produce tetrahydromenaquinone-9 [MK-9 (4H)] as a major menaquinone (vitamin K2). This study aimed to determine the MK-9 (4H) concentration in commercial propionibacteria-fermented cheese. The MK-9 (4H) concentration was quantified using an HPLC instrument with a fluorescence detector after postcolumn reduction. Among the various cheese samples, the MK-9 (4H) concentration was highest in Norwegian Jarlsberg cheese, followed by Swiss Emmental cheese. In contrast, the MK-9 (4H) concentrations in Appenzeller or Gruyère cheeses were extremely low or undetected. Likewise, the concentrations in Comte and Raclette cheeses were lower than those in Jarlsberg and Emmental cheeses. In the present study, the MK- 9 (4H) concentration in cheese showed a correlation with the viable propionibacterial cell count and propionate concentration. This implies that the increase in propionibacteria contributed to the generation of MK-9 (4H) in cheese. We presumed, based on these results, that Swiss Emmental and Norwegian Jarlsberg cheeses contain a meaningful amount of vitamin K because of their high MK-9 (4H) concentrations (200 to 650 ng/g).”
Kamao M, Suhara Y, Tsugawa N, Uwano M, Yamaguchi N, Uenishi K, Ishida H, Sasaki S, Okano T. (2007) Vitamin K content of foods and dietary vitamin K intake in Japanese young women. Journal of Nutritional Science and Vitaminology. 53(6):464-70. (Pubmed).
“Several reports indicate an important role for vitamin K in bone health as well as blood coagulation. However, the current Adequate Intakes (AI) might not be sufficient for the maintenance of bone health. To obtain a closer estimate of dietary intake of phylloquinone (PK) and menaquinones (MKs), PK, MK-4 and MK-7 contents in food samples (58 food items) were determined by an improved high-performance liquid chromatography method. Next, we assessed dietary vitamin K intake in young women living in eastern Japan using vitamin K contents measured here and the Standard Tables of Food Composition in Japan. PK was widely distributed in green vegetables and algae, and high amounts were found in spinach and broccoli (raw, 498 and 307 microg/100 g wet weight, respectively). Although MK-4 was widely distributed in animal products, overall MK-4 content was lower than PK. MK-7 was observed characteristically in fermented soybean products such as natto (939 microg/100 g). The mean total vitamin K intake of all subjects (using data from this study and Japanese food composition tables) was about 230 microg/d and 94% of participants met the AI of vitamin K for women aged 18-29 y in Japan, 60 microg/d. The contributions of PK, MK-4 and MK-7 to total vitamin K intake were 67.7, 7.3 and 24.9%, respectively. PK from vegetables and algae and MK-7 from pulses (including fermented soybean foods) were the major contributors to the total vitamin K intake of young women living in eastern Japan.”
Koivu-Tikkanen TJ, Ollilainen V, Piironen VI. (2000) Determination of phylloquinone and menaquinones in animal products with fluorescence detection after postcolumn reduction with metallic zinc. Journal of Agriculture and Food Chemistry. 48(12):6325-31. (Pubmed).
“A high-performance liquid chromatographic (HPLC) method for the determination of phylloquinone and menaquinones in foods of animal origin is described. The K vitamers were quantified with a fluorescence detector after postcolumn reduction with metallic zinc using K1(25) as an internal standard. Extraction was done either with 2-propanol-hexane (meat and fish products) or with acid hydrolysis method (dairy products). Prior to quantification, sample extracts were purified by semipreparative HPLC; in addition, the fats of cheese and rainbow trout samples were removed with lipase hydrolysis. By this method the phylloquinone and menaquinones (MK-4 to MK-10) present in a few representative samples of different animal food groups were determined. HPLC-MS was used to confirm the identification of K vitamers. Long-chain menaquinones were found from bovine and pig livers as well as from various cheeses. The total vitamin K contents calculated as the sum of quantified K vitamers were in general low (mean content 10-100 ng/g); the highest amount was analyzed in chicken meat (600 ng/g).”
Manoury E, Jourdon K, Boyaval P, Fourcassié P. (2013) Quantitative measurement of vitamin K2 (menaquinones) in various fermented dairy products using a reliable high-performance liquid chromatography method. Journal of Dairy Science. 96(3):1335-46. (Pubmed).
“We evaluated menaquinone contents in a large set of 62 fermented dairy products samples by using a new liquid chromatography method for accurate quantification of lipo-soluble vitamin K(2), including distribution of individual menaquinones. The method used a simple and rapid purification step to remove matrix components in various fermented dairy products 3 times faster than a reference preparation step. Moreover, the chromatography elution time was significantly shortened and resolution and efficiency were optimized. We observed wide diversity of vitamin K(2) contents in the set of fermented dairy products, from undetectable to 1,100 ng/g of product, and a remarkable diversity of menaquinone forms among products. These observations relate to the main microorganism species currently in the different fermented product technologies. The major form in this large set of fermented dairy products was menaquinone (MK)-9, and contents of MK-9 and MK-8 forms were correlated, that of MK-9 being around 4 times that of MK-8, suggesting that microorganisms able to produce MK-9 also produce MK-8. This was not the case for the other menaquinones, which were produced independently of each other. Finally, no obvious link was established between MK-9 content and fat content or pH of the fermented dairy products.”
Schurgers LJ, Vermeer C. (2000) Determination of phylloquinone and menaquinones in food. Effect of food matrix on circulating vitamin K concentrations. Haemostasis. 30(6):298-307. (Pubmed).
“Fluctuations in international normalized ratio values are often ascribed to dietary changes in vitamin K intake. Here we present a database with vitamin K(1) and K(2) contents of a wide variety of food items. K(1) was mainly present in green vegetables and plant margarins, K(2) in meat, liver, butter, egg yolk, natto, cheese and curd cheese. To investigate the effect of the food matrix on vitamin K bioavailability, 6 healthy male volunteers consumed either a detergent-solubilized K(1) (3.5 micromol) or a meal consisting 400 g of spinach (3.5 micromol K(1)) and 200 g of natto (3.1 micromol K(2)). The absorption of pure K(1) was faster than that of food-bound K vitamins (serum peak values at 4 h vs. 6 h after ingestion). Moreover, circulating K(2) concentrations after the consumption of natto were about 10 times higher than those of K(1) after eating spinach. It is concluded that the contribution of K(2) vitamins (menaquinones) to the human vitamin K status is presently underestimated, and that their potential interference with oral anticoagulant treatment needs to be investigated.”