A Dietitian’s Guide to Vitamin K

Your body needs vitamin K to perform a number of functions that support your everyday health. Vitamin K is a fat-soluble vitamin—along with vitamins A, D, and E—which means it’s best absorbed in dietary fat and stored in your body’s fatty tissues.  

Vitamin K was discovered in the 1920s when Danish researcher Henrik Dam observed that it could help prevent chickens fed a fat-free diet from bleeding to death. Dam named it the “koagulation vitamin” based on the German spelling of the word, and from there, it became known as vitamin K. 

Not getting enough vitamin K can have negative health effects, so it’s important to understand where to find it in your diet. What is vitamin K good for, how much do you need, and should you consider vitamin K supplements? Let’s dive into everything you should know about vitamin K.  

Vitamin K Functions

Vitamin K acts as a coenzyme for numerous critical processes to occur within the body.  

First off, this is the vitamin mostly required for blood coagulation. Vitamin K acts as a coenzyme in the synthesis of proteins involved in forming blood clots or coagulation. In other words, this helps blood clot so your body can form a scab and heal a wound.  

Vitamin K also plays a role in maintaining your bone health. It helps to strengthen bones by producing osteocalcin, a protein hormone that helps prevent low bone density and reduces the risk for fractures. Some research suggests that vitamin K2 helps enhance the ability of calcium and vitamin D to do their job in supporting bone metabolism.  

Vitamin K1 vs. Vitamin K2 

While you’ve probably heard of vitamin K, this is a generic name for a family of two compounds called phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2). 

• Vitamin K1 is the predominant form found in foods we regularly eat, making up most of our dietary intake. One of the best places to find it is leafy green vegetables.

• Vitamin K2 originates from bacteria. This is found in certain animal-derived foods as well as fermented foods. If you’re wondering where vitamin K is produced in the body, most menaquinones are also made by bacteria living in our digestive tract. It’s uncertain how much we actually get from vitamin K produced this way, but it’s presumed that it meets at least some of our daily needs. 

How Much Vitamin K Do You Need? 

While many nutrients have a Recommended Dietary Allowance (RDA), vitamin K has an Estimated Average Requirement (EAR). This is the average daily amount of vitamin K estimated to meet the requirements of 50% of healthy people. The EAR for vitamin K is as follows:  

• Birth to 6 months: 2 mcg  

• 7–12 months: 2.5 mcg  

• 1–3 years: 30 mcg  

• 4–8 years: 55 mcg  

• 9–13 years: 60 mcg  

• 14–18 years: 75 mcg 

• 19+ years, males: 120 mcg  

• 19+ years, females: 90 mcg 

Vitamin K Deficiency 

Most people in Western countries like the United States get enough vitamin K from their diet alone, and true vitamin K deficiency reports are rare. It’s most likely to occur in the event of severe malnutrition.  

Still, there are certain groups of people who are considered to be at a higher risk for developing vitamin K deficiency. Two of the highest-risk groups include infants not given the standard vitamin K1 supplement at birth and individuals with malabsorption disorders that can prevent optimal nutrient absorption.  

True vitamin K deficiency can contribute to excessive bleeding, poor bone development, and an increased risk of heart problems. 

Getting Too Much Vitamin K

Excessive intake of fat-soluble vitamins can be concerning because of how they are stored in the body. Unlike excess water-soluble vitamins, which are excreted in the urine, fat-soluble vitamins accumulate in the fatty tissues and organs. 

This can have toxic effects in some cases, particularly when overconsumption is due to the use of supplements. However, there is no established Upper Limit—the maximum daily intake unlikely to cause adverse health effects—for vitamin K due to its low potential for toxicity from foods or supplements.   

Vitamin K Foods 

Vitamin K is found in a wide variety of foods, which explains why not getting enough of this nutrient is uncommon for most people. It’s likely found in several foods you already eat and others you might consider adding to your diet. Let’s take a look at food sources of vitamin K1 and vitamin K2.  

Some food sources of vitamin K1 include: 

• Leafy greens, such as spinach, arugula, lettuce, collards, and turnip greens 

• Cruciferous vegetables, like broccoli, Brussels sprouts, and kale 

• Roasted soybeans 

• Carrot juice 

• Okra 

• Canned pumpkin 

• Blueberries 

• Grapes 

• Cashews 

Find vitamin K2 in the following foods:  

• Natto, a sticky Japanese fermented soybean dish 

• Chicken breast 

• Eel 

• Certain cheeses, like cheddar, Munster, and aged Gouda 

• Beef liver 

• Sauerkraut and kimchi 

• Fermented pickles 

• Egg yolk 

• Tempeh 

Should You Take a Vitamin K Supplement?

Some people may benefit from a vitamin K supplement, such as Vitamin Code D3 & K2 Gummies in raspberry lemon flavor. Plus, many daily multivitamins include 100% of the daily value of vitamin K, which may be helpful for some people like post-menopausal women and athletes.  

Always speak to your healthcare provider before adding any new supplement to your routine to ensure it’s safe and appropriate.  

Potential Interactions 

Because of vitamin K’s involvement in blood clotting, it’s important for individuals taking anticoagulant medications, such as Warfarin (Coumadin®), to be aware of their intake of the nutrient. These types of drugs have the opposite effect of vitamin K, which can interfere with their effectiveness. 

Maintaining a consistent intake of vitamin K—meaning not making significant changes in existing vitamin K intake habits—when on anticoagulant medications is key. For instance, if you’re prescribed this medication, it’s not a good time to start eating a big bowl of spinach every day if you haven’t been doing that already. If you take these types of drugs, work with your doctor or registered dietitian to ensure your dietary vitamin K intake is stable.  

Tips for Increasing Your Vitamin K Intake 

If you’re not sure whether you’re eating enough vitamin K in your diet, here are some ways you can incorporate the vitamin K foods above: 

• Try natto on top of steamed rice for lunch 

• Enjoy a mixed green salad or add leafy greens to sandwiches and wraps 

• Add greens to homemade pesto sauce tossed with noodles 

• Sauté collards or turnip greens alongside your meal 

• Use canned pumpkin in homemade muffins and pumpkin bread 

• Toss blueberries in oatmeal or smoothies 

• Enjoy a glass of carrot juice in the morning 

• Try sauerkraut on sandwiches, burgers, or with Buddha bowls 

Takeaway 

Vitamin K is an important nutrient involved in many aspects of health, including keeping your bones strong and allowing your blood to form clots when necessary. Both vitamin K1 and K2 are found in a variety of plant, animal, and fermented foods that can be easily incorporated into your diet. While most people meet their daily needs for vitamin K through food, some may consider a vitamin K supplement to help fill in the gaps, with the guidance of their healthcare provider. 

References 

1. Tsugawa N, Shiraki M. Vitamin K Nutrition and Bone Health. Nutrients. 2020;12(7):1909. Published 2020 Jun 27. doi:10.3390/nu12071909 

2. Capozzi A, Scambia G, Migliaccio S, Lello S. Role of vitamin K2 in bone metabolism: a point of view and a short reappraisal of the literature. Gynecol Endocrinol. 2020;36(4):285-288. doi:10.1080/09513590.2019.1689554 

3. Vitamin K: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements. Updated 29 March 2021. Accessed 12 April 2023. Available from: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/  

4. Eden RE, Coviello JM. Vitamin K Deficiency. [Updated 2022 Jul 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536983/ 

5. Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press (US); 2001.