Vitamin K2: Part One
January 16th, 2014 by Jack Norris RDIn the past year and a half, vitamin K2 has been the second most common topic, after oxalate, that I’ve received questions about.
Vitamin K2 is relevant to vegan diets because the only plant food that has an appreciable amount is natto, a fermented soy product that most of us don’t eat and which has a taste many people don’t care for.
Until recently, mainstream science has considered K2 to be unnecessary both because people can get the same benefits from K1 (which is found in leafy greens) and because K2 is made by common intestinal bacteria. But then research came out at the end of the 00’s suggesting that K2 might have benefits.
K2 is now being used to promote eating animal products such as in the article Vitamin K2: A Little Known Nutrient Can Make a Big Difference in Heart and Bone Health, by Aglaée Jacob, MS, RD, CDE in Today’s Dietitian (June 2013). Jacob promotes animal products to prevent heart disease because of the vitamin K2.
As an aside, I’m not sure if this is Today’s Dietitian’s position on saturated fat and animal products, but it’s not the only article they have run in which Jacob jettisons the idea that saturated fat causes heart disease (see also Coconut Oil – Learn More About This Superfood That Contains Healthful Saturated Fats).
My plan is to review the studies on K2 more closely to try to figure out to what extent, if any, vegans are setting themselves up for heart disease, osteoporosis, or other diseases by not having an intake of vitamin K2.
A quick refresher on the forms of vitamin K:
– Phylloquinone is vitamin K1 and found primarily in plant foods, especially leafy greens.
– Menaquinone (forms MK4 through MK10) is vitamin K2. It is found in animal tissues and made by bacteria.
More background info can be found in the article vitamin K at VeganHealth.org.
The first study I’ll review is from one of the two Dutch cohorts of the European Prospective Investigation Into Cancer (EPIC). It was published in 2009 (1). They followed over 16,000 women for an average of 8 years.
The researchers did a fairly rigorous job in measuring vitamin K intake which ranged from 1 – 128 µg, with an average of 29 µg.
They found that every 10 µg increase in vitamin K2 intake was associated with an decreased risk of heart disease but the finding was of only borderline statistical significance (.92, .85 – 1.00). Interestingly, even though they divided the group into quartiles of vitamin K2 intake, they did not report on the relative risk between the different quartiles.
In contrast, intake of vitamin K1 was not associated with risk of heart disease.
Unlike Aglaée Jacob, the authors caution against getting vitamin K2 through typical animal foods:
“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.”
I’m skeptical that their findings have important practical implications for cardiovascular disease prevention, but I’ll be reviewing other papers in the days ahead to find out more.
References
1. 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. | link