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Vitamin K
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Food Nutrition

Vitamin K

Vitamin K is essential for blood clotting and the development of healthy bones and tissues.

Overview

Vitamins are substances that your body needs to grow and develop normally. Vitamin K helps your body by making proteins for healthy bones and tissues. It also makes proteins for blood clotting. If you don't have enough vitamin K, you may bleed too much.

Important Considerations

Newborns have very little vitamin K. They usually get a shot of vitamin K soon after they are born.

If you take blood thinners, you need to be careful about how much vitamin K you get. You also need to be careful about taking vitamin E supplements. Vitamin E can interfere with how vitamin K works in your body. Ask your health care provider for recommendations about these vitamins.

Sources

There are different types of vitamin K. Most people get vitamin K from plants such as green vegetables, and dark berries. Bacteria in your intestines also produce small amounts of another type of vitamin K.

Frequently Asked Questions

Newborns are born with very low levels of vitamin K because it does not cross the placenta easily, and their gut bacteria, which produce some vitamin K, have not yet established themselves. Without this initial dose, babies are at risk for Vitamin K Deficiency Bleeding (VKDB), a serious condition that can cause internal bleeding, including in the brain. The injection ensures they have enough vitamin K to clot blood properly in the first few weeks of life.
The most common sign of vitamin K deficiency is excessive bleeding or bruising, such as nosebleeds, bleeding gums, or blood in the urine or stool. In severe cases, it can lead to internal bleeding. However, true dietary deficiency is rare in healthy adults because vitamin K is widely available in foods and produced by gut bacteria. Deficiency is more common in people with malabsorption disorders, those on long-term antibiotics, or those with liver disease.
Vitamin K directly counteracts the effects of warfarin and other vitamin K antagonist blood thinners. Warfarin works by blocking the action of vitamin K, so consuming large amounts of vitamin K-rich foods or supplements can reduce the effectiveness of the medication and increase the risk of blood clots. Patients on these medications should maintain a consistent intake of vitamin K rather than avoiding it entirely, and they must inform their doctor before taking any new supplements.
The best sources of vitamin K1 are dark green leafy vegetables, such as spinach, kale, collard greens, and Swiss chard. Other good sources include broccoli, Brussels sprouts, and avocados. Vitamin K2, which is important for bone and heart health, is found in fermented foods like natto, cheese, and egg yolks, as well as in some animal products. Incorporating a variety of these foods into your diet helps ensure adequate intake.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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