Get to Know Vitamin K

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Get to Know Vitamin K

With vitamin K, we’ve reached the end of our vitamin journey (see the links at the bottom of this article for our full vitamin rundown). Vitamin K is actually a generic name for a group of vitamins, and as you’ll see, this vitamin plays a few unique roles in the body.

What is vitamin K?

Vitamin K gets its name from the German word Koagulationsvitamin. This fat-soluble vitamin consists of a family of compounds, including phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2). Phylloquinone is found primarily in green vegetables and is the main dietary form of vitamin K. Menaquinones, on the other hand, are produced by bacteria in the gut and are also found in animal-based foods and fermented foods.

What does vitamin K do?

Vitamin K’s job is to make proteins for blood clotting (hence the name Koagulationsvitamin) and healthy bones and tissues. Prothrombin, or clotting factor II, is a vitamin-K-dependent protein that is directly involved in blood clotting. This is important to know if you take a blood thinner drug, such as warfarin (brand name Coumadin). Vitamin K can counteract the effect of warfarin, leading to the production of clotting factors, causing the blood to clot. Changes in the amount of vitamin K that you consume can affect how warfarin works. Your health care provider may advise you to maintain a consistent intake of vitamin K if you take warfarin.

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In addition to helping to make prothrombin, vitamin K is needed to make osteocalcin, a protein that’s found in bone, and matrix Gla-protein (MGP), which is present in vascular smooth muscle, bone, and cartilage.

Vitamin K in the body is found in the liver, brain, heart, pancreas, and bone. Also, gut bacteria make vitamin K, helping to meet some of the body’s requirement for this vitamin.

Because vitamin K is involved in promoting bone health, researchers believe that this vitamin may reduce the risk of bone fractures, especially in postmenopausal women, who are at risk for osteoporosis. Low levels of vitamin K are linked with low bone density; data from the Nurses’ Health Study indicate that women consuming at least 110 micrograms of vitamin K daily are 30% less likely to break a hip compared with women who consume less than 110 micrograms. And, Framingham Heart Study data shows a link between a high vitamin K intake and a lower risk of hip fracture in both men and women, and higher bone mineral density in women. But more research is needed to establish this vitamin’s role in reducing bone fractures.

Vitamin K may also play a role in fighting heart disease. A study published in 2021 in the Journal of the American Heart Association followed more than 53,000 Danish adults and tracked hospitalizations for heart disease, stroke and peripheral artery disease (PAD). People with the highest vitamin K intake from leafy green vegetables and vegetable oils were 21% less likely to be hospitalized for these events compared to people with lower vitamin K intakes. The authors speculated that vitamin K may work to fight heart disease by blocking inflammation and calcium buildup. However, more research is needed to understand the possible role of vitamin K in heart disease prevention.

What foods have vitamin K?

Food sources of phylloquinone (vitamin K1) include:

  • Green leafy vegetables, such as spinach, kale, broccoli, lettuce, collards
  • Some fruits, such as blueberries and figs
  • Vegetable oils, especially soybean and canola oils
  • Salad dressings made with vegetable oils
  • Fortified meal replacement shakes

Food sources of menaquinones (vitamin K2) include:

  • Meat
  • Cheese
  • Eggs
  • Soybeans

Vitamin K is found in multivitamin/mineral supplements, as well as supplements of just vitamin K or vitamin K along with some other nutrients.

How much vitamin K do you need?

The Recommended Daily Allowance for vitamin K is:

  • For adult men 19 years and older: 120 micrograms (mcg)
  • For women 19 years and older: 90 mcg
  • For pregnant or breastfeeding women: 90 mcg

What are signs of vitamin K deficiency?

Most people in the U.S. get enough vitamin K from foods, and bacteria in the gut makes some, too, so a deficiency is rare. But there are people who may have trouble getting enough of this vitamin:

  • Infants who don’t get a vitamin K injection at birth
  • People who have cystic fibrosis, celiac disease, ulcerative colitis, Crohn’s disease, short bowel syndrome, gallbladder disease, or liver disease
  • People on long-term hemodialysis
  • People who have had bariatric (weight-loss) surgery

A vitamin K deficiency can cause:

  • Bruising
  • Excessive bleeding
  • Heavy menstrual periods
  • Stomach bleeding with possible vomiting with blood
  • Osteoporosis

Vitamin K can be affected by taking antibiotics for more than a few weeks. The antibiotics can kill off bacteria that make vitamin K. Also, bile acid sequestrants, which are used to lower cholesterol levels and the drug orlistat (a weight-loss drug) can decrease the amount of vitamin K that your body absorbs.

If you take any of the above medications or take supplements that contain vitamin K, talk with your health care provider to learn if these might interfere with how your body absorbs and uses vitamin K. Vitamin K deficiency is treated by taking this vitamin orally or as an injection.

What are signs of vitamin K toxicity?

Vitamin K has not been found to be harmful, but if you take warfarin, the blood thinner, and you don’t keep your vitamin K intake consistent, you may develop blood clots if you consume more than your usual amount of vitamin K.

Other things to know about vitamin K

Newborns in the U.S. are given vitamin K injections to help prevent bleeding. This is because babies are born without bacteria in their intestines, and they don’t get enough vitamin K from breast milk.

To help your body absorb vitamin K from food, eat foods rich in vitamin K with a healthy fat source, such as a vegetable oil, avocado, nuts, or olives.

Get to Know Vitamin A

Get to Know Vitamin B1

Get to Know Vitamin B2

Get to Know Vitamin B3

Get to Know Vitamin B5

Get to Know Vitamin B6

Get to Know Vitamin B7

Get to Know Vitamin B9

Get to Know Vitamin B12

Get to Know Vitamin C

Get to Know Vitamin D

Get to Know Vitamin E

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES on social media

A Registered Dietitian and Certified Diabetes Educator at Good Measures, LLC, where she is a CDE manager for a virtual diabetes program. Campbell is the author of Staying Healthy with Diabetes: Nutrition & Meal Planning, a co-author of 16 Myths of a Diabetic Diet, and has written for  publications including Diabetes Self-Management, Diabetes Spectrum, Clinical Diabetes, the Diabetes Research & Wellness Foundation’s newsletter,, and

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