Vitamin K: everything you need to know

Think back to the last time you fell and scraped your knee or found yourself on the receiving end of an unforgiving paper cut. If those wounds stopped bleeding pretty quickly and healed in a timely manner, you have vitamin K—which plays a role in helping your blood clot properly—to thank for that (along with a few other blood-clotting proteins, but more on those later).

Fortunately, being deficient in this vitamin is rare because your body already makes some of it in your gut. The rest of it comes from foods like spinach and kale, as well as some meats and cheeses (Imbrescia, 2021). Let’s take a more in-depth look at vitamin K. 

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Vitamin K is a fat-soluble vitamin that helps your blood clot properly. Fat-soluble vitamins are nutrients that your body stores and processes in a specific way. You need to consume them regularly for your body to function properly (Reddy, 2021). 

It exists in two forms: vitamin K1—also called phylloquinone—and vitamin K2. Phylloquinone is the form of vitamin K present in most food sources, whereas vitamin K2 exists in a few different forms, otherwise known as menaquinones. While vitamin K2 is in some foods, it is also made by intestinal bacteria (the bacteria in your gut) (Halder, 2019). 

From time to time, you may run across medical articles that refer to vitamin K2 as MK-4. This is a specific form of vitamin K2 the body makes from vitamin K1. Gut bacteria play no part in the creation of this type of K2 (Fusaro, 2017). 

Even though the body creates small amounts of vitamin K, it is important to get it from dietary sources to reap its benefits (Fusaro, 2017). 

When it comes to vitamin K’s benefits, its most prominent is that it helps your blood clot (or coagulate). It does this by helping your body produce a specific substance called vitamin K-dependent carboxylase. Vitamin K-dependent carboxylase allows your body to produce the proteins it needs for your blood to clot (NIH, 2021). 

In addition to producing these proteins, vitamin K also assists other blood-clotting proteins like prothrombin, which is dependent on vitamin K. In other words, without vitamin K, your body cannot produce prothrombin (NIH, 2021). Aside from helping with coagulation, vitamin K also helps your body maintain healthy bones and blood vessels by supporting various vitamin K-dependent proteins (Tsugawa, 2020).

For women ages 19 and older, an adequate vitamin K intake is about 90 mcg a day. For men ages 19 and older, an adequate vitamin K intake is about 120 mcg a day. Most people don’t require vitamin K supplements to reach these numbers as they get a proper amount from their bodies and the foods they eat. The risk of getting too much vitamin K is extremely low. Currently, there is no established upper-level intake of vitamin K (NIH, 2021). 

People on certain medications are more at risk for imbalances of vitamin K. For example, people taking Coumadin (Warfarin) or other medications that influence the blood's ability to clot need to consume a consistent amount of vitamin K. When on warfarin, your risk of bleeding increases if you do not get enough vitamin K, but too much of the vitamin can hamper warfarin's anti-clotting ability. If you are on warfarin, consult a healthcare provider before making dietary changes like increasing your vitamin K intake (NIH, 2021). 

One indirect way to measure abnormalities in vitamin K levels is to look at the prothrombin time. Prothrombin time is a measurement of how long it takes for your blood to clot. When this level is abnormal (i.e., it takes longer than average for you to stop bleeding), it could indicate that your vitamin K level is also abnormal (NIH, 2021). 

However, healthcare providers don’t routinely check for vitamin K deficiency in people without telltale symptoms like bleeding or bruising (NIH, 2021). Before running any blood tests, healthcare providers consider someone’s medical history and any factors that might increase the risk for vitamin K deficiency, such as taking anticoagulants.

In general, vitamin K1 is primarily present in plant sources, and vitamin K2 is present mainly in animal sources. Some foods contain both types of vitamin K. For example, sauerkraut and some cheeses both have vitamin K1 and vitamin K2 (Halder, 2019).

Leafy green vegetables, like collards, turnips, spinach, kale, and broccoli, are excellent sources of vitamin K1. And, if you need a break from greens, fruits and nuts like kiwis, blueberries, avocadoes, pine nuts, and cashews, also contain the vitamin. (Halder, 2019).

Vitamin K2 is not as easy to get from food sources. However, some foods, particularly those where bacteria is involved in their production, have vitamin K2. For example, some cheeses contain vitamin K2. Here are a few other food sources of vitamin K2 (Halder, 2019; NIH, 2021):

• Chicken

• Beef and pork liver

• Natto, a fermented food that many people in Japan eat

• Shrimp

• Cheddar cheese

• Egg yolks

Deficiency of vitamin K is rare, particularly in people who eat a varied diet. Often, people with a deficiency don't have any symptoms. But, if the deficiency is severe, bleeding can occur. This tends to happen to people on certain medications or with certain malabsorption conditions (Eden, 2021). Someone with vitamin K deficiency may also bruise easily and have an elevated prothrombin time (Reddy, 2021).

People at risk for a deficiency include those with malabsorption conditions like cystic fibrosis, ulcerative colitis, and celiac disease. Those who have had part of their intestine removed or who have had bariatric surgery may also develop vitamin K deficiency (NIH, 2021). Finally, antibiotics interfere with gut bacteria and can also put you at risk for a deficiency (Reddy, 2021).

Sometimes, correcting a vitamin K deficiency just involves diet changes or the use of supplements. In cases of severe bleeding, you might need a vitamin K IV injection, as directed by your healthcare provider (Eden, 2021). 

Deficiencies in newborns occur because vitamin K does not cross the placenta well, and breast milk has low levels of the vitamin. Finally, newborns' gut bacteria is not yet well-developed. 

In infants, deficiencies occur because vitamin K does not cross the placenta well, breast milk has low levels of the vitamin, and their gut bacteria is not yet well-developed. This deficiency can cause vitamin K deficiency bleeding (VKDB). VKDB can cause internal bleeding and can potentially be life-threatening, which is why newborns receive doses of vitamin K at birth to help prevent a vitamin K deficiency (Eden, 2021; Araki, 2020). 

As you can see, vitamin K is a vitamin that holds great importance from the moment we’re born. Eating a varied diet that includes leafy green vegetables can help you get the vitamin K you need. However, if you are on certain medications or have a malabsorption disorder, or if you notice that your cuts and scrapes aren’t healing properly, ask your healthcare provider about your vitamin K intake. 

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Current version

November 04, 2021

Written by

Jessica Norris

Fact checked by

Felix Gussone, MD

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About the medical reviewer

Felix Gussone, MD, Ro

Felix Gussone is a physician, health journalist and a Manager, Medical Content & Education at Ro.