by Jack Norris, RD
- Blood Clotting and Bones
- Vitamin K2 and Cardiovascular Disease
- Fat and Vitamin K Absorption
Vitamin K is needed for proper blood clotting and bone health. Vegans who eat leafy green vegetables with some added oil on a daily basis should receive more than adequate vitamin K. Even those who do not might obtain enough vitamin K from intestinal bacteria, unless they have had a significant course of antibiotics. Making sure you get plenty of vitamin K through leafy green vegetables is the best plan.
Preliminary evidence indicates that vitamin K2 might reduce the risk of heart disease.
Blood Clotting and Bones
Vitamin K is a vitamin needed for blood clotting. It also has activity in bones and deficiency can result in bone fractures, especially in old age. The Dietary Reference Intake for vitamin K is 120 µg for men and 90 µg for women. Table 1 shows the vitamin K content of plant foods that are high in vitamin K.
Vitamin K refers to the chemical menadione and any derivatives of it that exhibit anti-hemorrhagic activity in animals fed a vitamin K-deficient diet. There are two types:
- Phylloquinone (K1) – found primarily in plant foods; most prevalent in green leafy vegetables. (1)
- Menaquinone (K2) – found in animal tissues and produced by bacteria. The only vegan food high in menaquinone is natto (998 µg per 100 g portion) (1). Has varieties MK-4 thru MK-9.
|Table 1. Vitamin K in Plant Foods2|
|Romaine lettuce||shredded||1 cup||48|
|Swiss chard||boiled||1/2 cup||286|
Because menaquinone is not found in plant foods, some laypeople have suggested you need to eat animal products in order to have adequate vitamin K status. The scientific consensus has been that either of the two types of vitamin K are adequate, especially regarding vitamin K’s blood clotting activity.
In the United States, enteral nutrition products, which are used for people who cannot eat normally and often provide the only nutrition they receive for months or years, contain phylloquinone for vitamin K (1) and these patients presumably do fine, with regard to blood clotting, with only phylloquinone in their diet.
Additionally, menaquinone is produced by a number of different bacteria species that typically live in the digestive tract of humans (1), and can be absorbed in the distal part of the small intestine (5). Unless someone has had significant antibiotic therapy, they should have plenty of such bacteria providing them with menaquinone.
It is difficult to induce vitamin K deficiency (measured by slow blood clotting) by removing vitamin K from the diet, presumably due to the production of vitamin K by intestinal bacteria (1). However, it is possible to induce vitamin K deficiency (slow blood clotting) through antibiotic therapy, indicating intestinal bacteria provide a significant amount of vitamin K (1).
One study measuring blood-clotting in vegetarians (3) and one study measuring blood-clotting in vegans (4) did not show them to have slow blood clotting times. An abnormal rate of blood clotting problems has not been apparent for children raised vegan from birth; it would be unusual for their diets to be supplemented with menaquinone.
It, therefore, seems safe to assume that vegans have no need for menaquinone supplementation; especially when it comes to blood clotting. But what about bone health? Again, apparently healthy vegans are probably getting plenty of menaquinone, if it’s even necessary to have in addition to phylloquinone, from gut bacteria.
There is evidence that elderly women can reduce their chance of bone fracture by supplementing with vitamin K, specifically phylloquinone (6). A literature search (May 2010) revealed no studies comparing phylloquinone to menaquinone with regard to bone health.
Vitamin K2 and Cardiovascular Disease
Summary – Preliminary evidence suggests that vitamin K2 could reduce the risk of heart disease, but the research is mixed and the positive findings come from only one country. More research is needed. If vitamin K2 reduces the risk of heart disease, it does not mean that eating animal products high in vitamin K2 will also reduce the risk, since animal products often contain other components that may increase the risk of heart disease more than vitamin K2 decreases it.
In 2004, a prospective study from The Netherlands, The Rotterdam Study, found a strong association between intake of vitamin K2 and a reduced risk for cardiovascular disease (8). In comparing the highest daily intake (> 33 µg) of vitamin K2 to the lowest (< 22 µg), the higher intake was associated with a 41% reduced risk for a diagnosis of heart disease (.59, .40-.86), a 57% reduced risk of death from heart disease (.43, .24-.77), and a 26% reduced risk of mortality (.74, .59-.92). In a cross-sectional component, they also found an inverse relationship between vitamin K2 and artery calcification. There was no reduced risk found with vitamin K1.
Another cross-sectional study from The Netherlands, EPIC-Prospect, found that the highest vitamin K2 intake, 42 µg/day, was associated with a reduced risk of coronary artery calcification (.80, .65–.98) in comparison to the lowest category of 18 µg/day (10). MK4 was the only vitamin K2 subtype that showed an individual trend towards less artery calcification.
There is a plausible reason why vitamin K2 could prevent heart disease while vitamin K1 does not. Vitamin K is needed for the production of a protein that has a strong affinity for calcium (11). And while vitamin K1 is primarily cleared from the bloodstream by the liver for use in blood coagulation, vitamin K2 remains in the blood where it can prevent calcium from being deposited in artery walls (11).
Another bit of evidence was a clinical trial in which people on dialysis with osteoporosis were given 45 mg/day of vitamin K2 and after six months, their LDL cholesterol had gone from 225 to 195 mg/dl. After treatment was discontinued, cholesterol levels returned to normal (9). However, 45 mg/day of vitamin K2 is about 1,000 times more than a normal intake, and these are very high LDL levels in a rather ill population; the clinical relevance of this is doubtable.
While The Rotterdam Study had a strong finding for vitamin K2, other cohorts have not been quite so convincing.
A prospective study from EPIC-PROSPECT (2009) followed over 16,000 women for an average of 8 years. Vitamin K2 intake ranged from 1 – 128 µg, with an average of 29 µg. They found that each 10 µg increase in vitamin K2 was associated with a decreased risk of heart disease but the finding was only of borderline statistical significance (.92, .85 – 1.00).
In contrast to the findings from The Netherlands, in the EPIC-Heidelberg cohort from Germany (12), it was vitamin K1 (from plants) that was found to be inversely associated with a fatal heart attack (.49, .25-.94), while K2 was associated with increased incidence of heart disease (1.21, .81–1.80) and increased fatal heart attack (1.09, .46–2.62), although neither finding was statistically significant. Results were adjusted for smoking, body mass index, waist circumference, hypercholesterolemia, high blood pressure, aspirin use, physical activity, education, and intakes of energy, fat, alcohol, calcium, and folate.
Another prospective study from The Netherlands combined data from EPIC-Prospect and EPIC-Morgen (13) and looked at the association between vitamin K2 intake and stroke. No association was found, though the authors pointed out that artery calcification may not be a cause of stroke as it is for heart disease.
And another paper of combined data from EPIC-Prospect and EPIC-Morgen (14) found a trend towards a lower risk of diabetes in comparing the upper intake (49 µg) to the lower (15 µg), although the finding was not statistically significant (.80, .62–1.02). When looking at what effect an increase of 10 µg had on the risk of diabetes over the entire range of intakes, there was a borderline statistically significant beneficial association (.93, .87–1.00; p < .038).
From the research above, it appears that higher vitamin K2 intake could reduce the risk of heart disease. However, the only significant associations have come from one country, The Netherlands, and the findings have not been strong. Clinical trials are needed and, luckily, at least one is underway (15).
Even if vitamin K2 reduces the risk of heart disease, it doesn’t mean that animal products high in vitamin K2 reduce the risk. The authors of the 2009 EPIC-PROSPECT report caution against getting vitamin K2 through typical animal foods (11):
Thus, although our findings may have important practical implications on [cardiovascular disease] prevention, it is important to mention that in order to increase the intake of vitamin K2, increasing the portion vitamin K2 rich foods in daily life might not be a good idea. Vitamin K2 might be, for instance more relevant in the form of a supplement or in low-fat dairy. More research into this is necessary.
Fat and Vitamin K Absorption
Vitamin K is a fat-soluble vitamin, and fat can significantly increase its absorption from food (7). Since green leafy vegetables naturally contain very little fat, it is a good idea to add some fat or oil when preparing them.
3. Mezzano D, Munoz X, Martinez C, Cuevas A, Panes O, Aranda E, Guasch V, Strobel P, Munoz B, Rodriguez S, Pereira J, Leighton F. Vegetarians and cardiovascular risk factors: hemostasis, inflammatory markers and plasma homocysteine. Thromb Haemost 1999 Jun;81(6):913-7.
4. Sanders TA, Roshanai F. Platelet phospholipid fatty acid composition and function in vegans compared with age- and sex-matched omnivore controls. Eur J Clin Nutr. 1992 Nov;46(11):823-31. Same study population as citation 25.
5. Conly JM, Stein K, Worobetz L, Rutledge-Harding S. The contribution of vitamin K2 (menaquinones) produced by the intestinal microflora to human nutritional requirements for vitamin K. Am J Gastroenterol. 1994 Jun;89(6):915-23. (Abstract)
8. Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, Hofman A, Witteman JC. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004 Nov;134(11):3100-5.
10. Beulens JW, Bots ML, Atsma F, Bartelink ML, Prokop M, Geleijnse JM, Witteman JC, Grobbee DE, van der Schouw YT. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis. 2009 Apr;203(2):489-93.
11. Gast GC, de Roos NM, Sluijs I, Bots ML, Beulens JW, Geleijnse JM, Witteman JC, Grobbee DE, Peeters PH, van der Schouw YT. A high menaquinone intake reduces the incidence of coronary heart disease. Nutr Metab Cardiovasc Dis. 2009 Sep;19(7):504-10.
12. Nimptsch K, Rohrmann S, Linseisen J, Kaaks R. Dietary intake of vitamin K and risk of incident and fatal myocardial infarction in the EPIC-Heidelberg cohort study Gesundheitswesen 2010; 72: V143-DOI: 10.1055/s-0030-1266323.
13. Vissers LE, Dalmeijer GW, Boer JM, Monique Verschuren WM, van der Schouw YT, Beulens JW. Intake of dietary phylloquinone and menaquinones and risk of stroke. J Am Heart Assoc. 2013 Dec 10;2(6):e000455.
14. Beulens JW, van der A DL, Grobbee DE, Sluijs I, Spijkerman AM, van der Schouw YT. Dietary phylloquinone and menaquinones intakes and risk of type 2 diabetes. Diabetes Care. 2010 Aug;33(8):1699-705. doi: 10.2337/dc09-2302. Epub 2010 Apr 27.
Rees K, Guraewal S, Wong YL, Majanbu DL, Mavrodaris A, Stranges S, Kandala NB, Clarke A, Franco OH. Is vitamin K consumption associated with cardio-metabolic disorders? A systematic review. Maturitas. 2010 Oct;67(2):121-8.