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From a young age, we learn the disappointing difference between our wants and needs. Maybe you unwrapped a birthday gift that had socks instead of a toy. Maybe you were deprived of dessert. Maybe you were forced to wear a helmet while riding a bike, even though you thought it didn’t look very cool. It’s a balancing act, and we can usually see how our choices play out.

Inside our bodies is a completely different story. We can’t see what’s happening. But if we focus on listening to what our bodies are trying to tell us instead of relying on visual cues, we may get a better sense of what they need. If you listen to your body when it tells you it’s cold, you know to put on more clothes.

The symptoms of a vitamin deficiency can be subtle, but you can train yourself to hear them.

The big sign of a vitamin K deficiency? It’s in your blood.

Vitamins: A Brief Introduction

You hear it all the time: you need vitamins and minerals to be fully operational. But knowing why you need them is a completely different story. The story of why you need vitamin K starts here.

Vitamins join minerals in a class of compounds known as micronutrients, which are balanced out in our diets by macronutrients. If you’ve ever calculated your macros (short for macronutrients) you know that these are composed of carbohydrates, proteins, and fats. These three energize you to do everything from reading this article to running a marathon, but they are defined by their existence alongside micronutrients for a full-body effect.

Defining a vitamin is a complex process.

A vitamin is a carbon-containing organic compound and natural component of foods. Vitamins are vital to our normal physiological functions, including growth and development.

They must be consumed through our diet because we aren’t able to synthesize them, with sunlight exposure to vitamin D being the exception. The rest of the animal kingdom also has an exception: vitamin C. While primates, guinea pigs, and invertebrates have to go looking for vitamin C through their diet, most animals can just synthesize their own.Combs2017

Even when you consume vitamins from your diet, they can be quite fickle. Because of their delicate structure, they don’t hold up well to things like cooking. If you microwave your broccoli, you’ll probably destroy its vitamin C content.Combs2017

An image of kimchee and broccoli, showing the basics of vitamin k in our foods

Vitamins are also particular about how they can be absorbed, and they’re lumped into two categories: water-soluble and fat-soluble. We can absorb fat-soluble vitamins through the intestinal tract with the help of dietary fats, like oil. These fats can be stored in our fatty tissues and livers for several days or longer. Water-soluble vitamins, like C, pass through the liquids in our bodies and must be replenished frequently. Translation? You pee them out, so make sure you’re keeping up with them.

Vitamin K: An Even Briefer Introduction

Now that we know what a vitamin is, let’s dive deeper into our featured nutrient: vitamin K.


Vitamin K was discovered when Henrik Damn experimented with low-fat diets and hemorrhaging chicks. When he discovered the missing fat-soluble coagulation (blood clotting) factor, he called it Koagulations vitamin, later shortened to vitamin K.Newman1998


There are two different types of vitamin K, known as K1 and K2. If you’re feeling ambitious, you can call them by their full names. K1 goes by phylloquinone, while K2 is known as menaquinone.Booth2012

Vitamin K1 is fat-soluble, which you may recall means it will dissolve in fats. For the best absorption, you should pair your vitamin K1 foods with a fat source, such as olive oil.Booth2012


Vitamin K1 is abundant in fresh food sources, such as kale, broccoli, and blackberries. It’s also found in nuts and legumes.Booth2012

Vitamin K2 has a slightly limited range of food sources because it’s a bacteria-based vitamin. It’s only present in fermented foods and animal products, such as cheese and egg yolks.Booth2012


Vitamin K plays an essential role in coagulation. In order to produce the proteins that get to work when coagulation is required, vitamin K must be present.

Vitamin K Deficiency

The body is pretty good at recycling its own supply of vitamin K, but that doesn’t mean you’re automatically protected from becoming deficient. In fact, there are many things at play when determining your vitamin K status that may seem unrelated.

How Deficiency Happens

Children’s intake of K1 is much lower today than it was in the mid-20th century because of dietary trends and changes, particularly the consumption of less leafy green vegetables.Prynne2005

While parents can preach to their children to finish their vegetables, they better start taking their own advice. Research shows that American adults are consuming less K1 and K2 than the US Food and Drug Administration’s dietary reference intakes.Booth1996

Newborns are the most at risk for becoming vitamin K deficient because the vitamin doesn’t transfer well from the mother’s placenta. Being breastfed doesn’t contribute either, as the vitamin is not very present in breast milk. Newborns’ bodies aren’t able to produce any vitamin K2 in their first few days of life. Even if they’re able to, their livers can’t efficiently utilize the vitamin just yet.Zipursky1999

This can lead to vitamin K deficiency bleeding, called VKDB. If VKDB is identified and treated right away, the outlook is generally good. However, brain damage or death is possible if the intracranial hemorrhage goes untreated. The American Academy of Pediatrics suggests going on the defensive by administering a single vitamin K injection at birth, especially if the mother is on anticoagulants.

Vitamin K deficiency can also be caused by malabsorption syndrome, which means the small intestine cannot absorb adequate levels of nutrients.

Malabsorption syndrome occurs via a number of outside factors: Crohn’s and celiac diseases, chronic pancreatitis, cystic fibrosis, liver disease, long-term antibiotic use, surgery and trauma-induced damage, radiation therapy, congenital defects, and the inability to produce certain digestive enzymes.Savvidou2009

You may already be taking certain medications that interact with your blood clotting capabilities. The most nefarious K conspirator is the blood thinner known as warfarin. Remember those proteins assisting K in the clotting convention? Coumarin anticoagulants like warfarin interfere with the production of these proteins. Antibiotics are also guilty of interfering by causing vitamin K to become less effective in the body. You’ll need a higher intake, but you may not be able to identify this need until the symptoms appear.

An image of a hand with a band-aid, illustrative of excessive bleeding, which is a symptom of vitamin k deficiency

How to Tell if You’re Deficient

You can probably guess the number one sign of vitamin K deficiency: excessive bleeding. In addition to the classic open wounds, the bleeding could be internal. Often, a person deficient in vitamin K will bleed into their own mucous membranes.

Look out for:

  • Excessive bleeding from an open wound
  • Bruising easily
  • Producing dark stool containing blood

However, the only way to truly know if you’re deficient is to go to your doctor.

Testing for Vitamin K Deficiency

Healthcare professionals generally test for vitamin K using the prothrombin time (PT) test. No need to study for this test; your blood has all the answers.

Your doctor will draw a small blood sample with a needle and induce clotting by adding chemicals. Based on how long it takes for your blood to clot, the doctor will determine if your vitamin K levels are low. The longer it takes, the greater the chance you’re deficient. Side note: it should take about 11 to 13.5 seconds for your blood to clot. But we don’t recommend trying this at home.

Vitamin K: Bonus Benefits

Proper coagulation is a need—no question there. But it’s not the only thing you’ll be wanting from adequate vitamin K intake, and it’s not the only thing this nutrient can do.

Illustrations of a bone and wrench, a dumbbell, a caution sign, and a brain with flexing arms, all showing the benefits of vitamin k

Bone Health

Vitamin K activates a special protein known osteocalcin, which is heavily involved in bone formation. Osteocalcin binds to calcium to build the mineral walls of teeth and bones, but it can’t create this bond without K2.Fang2012

Vitamin K status and bone strength share an association. An analysis of over 80,000 subjects found an inverse association between fracture risk and vitamin K status. As you may expect, subjects with the highest dietary intake of vitamin K had a lower fracture risk—by a whopping 22%.Hao2017 But that wasn’t the biggest reduction. With vitamin K administered in a mineral supplement, subjects in another study experienced a 35% reduction in their bone loss rate in the three years following the study.Braam2003

Heart Health

In addition to osteocalcin, vitamin K also regulates another protein: the matrix Gla protein (MGP).

The matrix Gla protein is important because it targets excess calcium ions floating around in your blood before they can attach to your arteries and cartilage.

If the calcium ions travel uninhibited, they can contribute to vascular calcification. Vascular calcification is a pretty big risk factor for heart disease.Geleijnse2004

The proof is in the research: two 2009 studies found that higher vitamin K2 intake was associated with reduced coronary calcification and reduced risk of coronary heart disease.Beulens2009,Gast2009

Brain Health

You’ve got vitamin K on your mind. Not just because you’re reading this article, but also because this coy clotting agent is a crucial nutrient for the central nervous system.Ferland2012

In particular, vitamin K modulates the metabolism of lipids present in high concentrations in cells of the central nervous system known as sphingolipids. Vitamin K regulates two proteins primarily involved in sphingolipid metabolism: Protein S, which assists in neuronal protection, and Gas6, which helps cells grow and survive.Ferland2012

Supplementing With Vitamin K

While getting vitamin K from leafy vegetables is a great start, taking a defensive approach with high doses may play an important role in other health factors, particularly if you unknowingly have low levels of vitamin K to start.

Make sure your vitamin K supplement includes both K1 and K2.

For the best results, aim to get between 50mcg - 100mcg of vitamin K1. For K2, aim higher, with a minimum of 100mcg. Remember that vitamin K supplements should be taken at mealtimes to increase absorption because the nutrient is fat-soluble.

For infants, ask your doctor about hemorrhagic disease of the newborn. They may administer a single dose of vitamin K ranging from 500mcg - 1,000mcg.

As always, consult your healthcare provider before taking any new supplements, particularly if you’re taking antibiotics or anticoagulants. If you’re concerned about hemorrhagic disease due to vitamin K deficiency, ask your doctor about coagulation tests.

Vitamin K for Your Needs and Wants

You need vitamin K for proper coagulation, but you may want some of the other benefits supplementation can provide, such as maintaining bone integrity, inhibiting vascular calcification, and synthesizing sphingolipids involved in cognitive functions.

Whether you’re actively battling deficiency or optimizing your daily functions, vitamin K is a bloody good boost.

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