The forgotten one you never really hear about, vitamin K’s main function in the body is its ability to prevent hemorrhaging and blood loss thanks to the role it plays in blood clotting. Its name even allegedly comes from ‘koagulation’, the Danish word for clotting.

In fact, so powerful are its clotting abilities, that UK doctors recommend all newborns receive a vitamin K shot to prevent a condition known as VKDB (of which, more later).

Not only that, there’s also evidence that Vit K also plays a significant role in helping to build our bones. Beyond that, things get a bit murkier, with no real consensus even as to what the safe upper limit of vitamin K should be.

Why might we start to hear a lot more about this vitamin?

Don’t be surprised if you start to hear a lot more about the mysterious K as our knowledge of the gut, and the hugely vital role our microbiome (the microorganisms living in our gut) plays in our mental and physical well-being, continues to expand.

Although our main source of K comes via compounds called phylloquinones present in our diet, menaquinones (another member of the vitamin K family of compounds) are produced by bacteria. So as well as finding menaquinones in modest amounts in animal-based and fermented foods, they can also be made independently by the bacteria in our gut. Which is pretty damn cool when you think about it.

Although it’s currently unclear exactly how much of this second type of vitamin K our body produces and absorbs, it’s an interesting new angle in the story of the vitamins, and one that I’m sure will be exploited further by marketers jumping on the ‘gut’ bandwagon as our fascination with the microbiome grows. The gut is just #sohotrightnow after all….

What’s K got to do with babies?

Babies are born with low levels of vitamin K. Although for most these stores are usually enough to prevent bleeding, a very small number of bairns - about one in 10,000 - have a snappily named condition known as ‘vitamin K deficiency bleeding’ (VKDB).

Essentially, this means that those babies deficient in vitamin K may bruise or bleed more easily than they should within the first 12 weeks or so of birth. Early warning signs are bleeding from the nose, mouth, or umbilical stump, but in a small percentage of cases the first bleed may be rather more serious – such as a bleed on the brain or in the gut for example, and harder to spot.

For this reason, doctors in the UK recommend that all babies receive a shot of vitamin K soon after birth. Perhaps invariably, this has led to the usual type of concern one gets with any opt-out medical intervention, and those against the vaccination are typically a subset of the anti-vac lot found in various angry corners of the internet.

How much do adults need?

Vitamin K is found in very low levels in our body, and rapidly metabolised, making it very much the odd one out in the usually longer-lasting fat-soluble vitamin group.

In the UK adults need 1 μg (microgram) per kg of body weight every day.

So for an average weighing 74kg, you need 74 μg per day. An average woman weighing around 60 kg, would need 60 μg/day and so on and so forth.

Anything else I need to think about in terms of getting enough?

Because Vitamin K is such an effective clotting agent, it can have a serious and potentially dangerous interaction with anticoagulant medication such as warfarin, which is often prescribed to those deliberately trying to thin their blood.

People taking warfarin and similar anticoagulants should consult a doctor or dietitian about their diet, and make sure to maintain a consistent intake of vitamin K from food and/or supplements as sudden changes in intake of K can increase or decrease the anticoagulant effect of these drugs.

What are good sources of the big K?

Foods rich in vitamin K include green leafy veg such as kale, spinach and broccoli, cereal grains, soy beans (in milk, tofu, oil, or on their own as edamame beans), yogurt, seeds and nuts, and vegetable oils.

In keeping with its general air of mystery, data on the bioavailability of different forms of vitamin K from food are very limited. But what we do know, is that as one of the fat-soluble vitamins, it can only be absorbed and digested by the body in the presence of fat. So adding a bit of olive oil or butter to your greens for example will help any K in your diet to be absorbed, although some foods (such as yogurt) will already provide fat alongside any vitamin K.

And what exactly am I supposed to do with that list of food stuffs?

Well I’m glad you asked, as that’s basically the entire point of The A to V. Try spicing up green veggies by mixing them with grains, such as in this Kale, orange and pecan quinoa,  or the Extra herby couscous recipe. Roast your sprouts rather than boiling them (roasted sprouts with lemon, chilli and garlic), or try a tofu and aubergine stir-fry for a speedy post-work dinner.

References

https://www.babycentre.co.uk/a551938/vitamin-k

https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/

Price, C. (2016) The Vitamin Complex. London, Oneworld Publications, p.106.