We’ve talked before about vitamin K2 MK-4 (also called menaquinone-4), an important vitamin for bone strength, brain development, and a whole host of measures of health we’re still discovering.  This particular form, menaquinone-4 (the name refers to the length of the molecule chain) seems to be especially important for human health.  It’s the primary form of vitamin K found in brain fats.  It’s the vitamin Weston Price first identified as “Activator-X,” observing its presence in the most sought-out and prized foods in the various cultures he studied.

Other animals like rats and ruminants can synthesize MK-4 from the plant form of vitamin K, known as vitamin K1 or phylloquinone.  Human beings can’t convert the plant form to MK-4, with one notable exception: women can, to some extent, convert phylloquinone to menaquinone-4 in breast milk, which is a sign that MK-4 is especially crucial for infant development.  Otherwise, we seem designed to get this vitamin from animal sources, just as our ancestors have been doing for millenia.

Vitamin K2 MK-4 is found in foods like grass-fed butter, organ meats, marrow and beef fat, as well as fish eggs, and the organs (and possibly the extracted fats) of some fatty fishes. 

It turns out there’s another good, inexpensive dietary source that will appeal more to some vegetarians (although not vegans, sorry): pasture-raised chicken eggs.

I started researching the vitamin K2 MK-4 content of eggs today after eating some remarkably orange-yolked eggs I bought at the farmers’ market from Woodring Orchards.  The eggs were from chickens which the owner’s eleven year-old daughter Caity raises on pasture -- the carton says Caity’s Fresh Eggs and features Caity’s hand-drawn label.  These eggs were hands-down the  best and darkest-yolked eggs I’ve had all season.  It’s always a treat to crack open an egg and be delighted by how dark orange the yolk is, signaling a wealth of vitamins, creamy texture and deep flavor.

I started thinking about how Weston Price correlated the deep yellow color in springtime butter with increased MK-4 content.  It was probably literally a sign of increased vitamin A (a strong correlation with increased vitamin K2 in this case), but it got me thinking how the color of egg yolks is also a sign of how nutritious they are (the darker the better).  We know from this study in Mother Earth News that eggs from pasture-raised chickens, which are the eggs that tend to have much darker yolks, have far more nutrients (fat soluble vitamins A and E, and DHA omega-3 fatty acids) than conventional supermarket eggs.  Chickens on pasture enjoy fresh greenery and nutritious bugs and worms.  The chickens get more nutrients, and pack their eggs with the converted forms we need.

Eggs from chickens on pasture also seem to be a good source of vitamin K2 MK-4. It turns out that chicks and chickens can convert phylloquinone and menadione (the usually synthetic K3) into MK-4. So it should be no surprise that MK-4 is, in fact, found in egg yolks.  And it seems eggs from chickens raised on pasture and taking in greater phylloquinone levels have more MK-4 in the yolks.

Chris Masterjohn sums this up nicely in this chart which groups data on vitamin K2 in egg yolks and other K2-rich foods.  He compares measures of MK-4 in egg yolks from this study in the U.S. and this study in the Netherlands.  The egg yolks from the Netherlands have twice the MK-4 content of their U.S. counterparts, presumably a result of diet.

If vitamin K2 MK-4 is in pasture-raised eggs, take this as another reminder eat real food grown and raised the way our ancestors did.  It’s also a reminder of both the value and the limitations of scientific research to date.  On one hand, we’re able to track down the specific nutrients that our ancestors have garnered from foods, analyze what these nutrients do in our body, and determine where we can find them.  On the other hand, there is a great deal we still don’t know.  If we’re only now discovering the value of menaquinone-4, what else have we not yet discovered?  We risk messing up the fine balance of our health when we change our diets (or other aspects of healthy living) too far from what our ancestors identified as the sustenance of healthy lives.

In addition to good science and traditional diets, we also have our instincts and taste buds to guide us.  The most orange egg yolks, the yellowest butter, the ripest berries... these foods are all better than their poor-quality counterparts, and it doesn’t take research much further than your mouth to figure that out.

The bottom line: eat delicious food that’s been produced in traditional and sustainable ways.  Eat this way both for the reasons we’re constantly figuring out, and for the reasons we don’t yet understand.