Chances are you’ve heard of vitamin K. Maybe you’ve spotted the name on the back of the label on a bag of spinach. But what is vitamin K, and what benefits does it offer? Here’s a refresher in the latest installment of our Simple Food Terms Explained series.

What Is Vitamin K?

Vitamin K is the generic name for a family of chemical compounds. These compounds consist of phylloquinone (vitamin K1), and several menaquinones (vitamin K2). Most natural sources of dietary vitamin come from vitamin K1, which is also easier to digest and carries less risk of toxicity.

In any form, vitamin K is important for the formation of proteins involved in blood clotting.

What Are The Benefits Of Vitamin K?

Vitamin K is primarily useful for treating issues with blood clotting. These issues include:

  • Infants with hemorrhagic disease caused by low vitamin K levels. A shot of vitamin K1 into the muscle is the most effective treatment.
  • People with low levels of prothrombin, a blood clotting protein. Vitamin K1 is taken orally or intravenously to treat and prevent excessive bleeding.
  • People with an inherited disease called vitamin K-dependent clotting factors deficiency (VKCFD). These people are prone to excessive bleeding as well, which can be treated with oral ingestion or an injection of vitamin K1.
  • People who have taken too much of the blood-thinning medication warfarin. Excessive blood thinning can be dangerous, so warfarin patients with low vitamin K levels may be advised to take a vitamin K supplement along with their warfarin.

When blood cannot clot, the results can be dangerous, potentially leading to internal bleeding and hemorrhage. Healthy levels of vitamin K are vital to prevent excessive bleeding or even bleeding out.

A specific form of vitamin K2 may also be an effective treatment in preventing osteoporosis, strengthening bones and reducing the risk of fractures in older women who are at risk. However, it doesn’t seem to have a benefit for men or for women whose bones are healthy.

Who Should Avoid Vitamin K Intake?

People who are on warfarin (also known as Coumadin) should avoid vitamin K unless otherwise directed by a doctor. Warfarin is prescribed to slow blood clotting, so too much vitamin K will cancel its effects. Warfarin patients should have regular blood tests to make sure their medication is working as intended.

Vitamin K1 intake may also decrease blood sugar, so diabetics should be cautious about taking too much vitamin K through diet or supplements. This is especially true for people taking diabetes medications that lower blood sugar, such as glimepiride, glyburide, insulin, pioglitazone, rosiglitazone, or others.

Which Foods Are Good Sources Of Vitamin K?

Adult men need approximately 120 mcg of vitamin K per day, while women need 90 mcg. Many foods are naturally rich in vitamin K, so deficiencies in healthy adults are rare. Vitamin K is also a part of many multivitamins and supplements.

Sources of vitamin K1 include:

  • leafy green vegetables, such as spinach, kale, and broccoli
  • canola oil
  • soybean oil

Sources of vitamin K2 include:

  • meats
  • eggs
  • fermented foods, such as cheese and soybeans

People with liver diseases or conditions that inhibit their body’s ability to absorb nutrients, such as celiac disease, ulcerative colitis, and cystic fibrosis, are more likely to be deficient in vitamin K. These people will need to make sure they’re eating enough vitamin-K rich foods in their diet.

Vitamin K is fat-soluble, so it’s best to eat foods rich in vitamin K along with a source of dietary fat, such as butter or oils, to reap the full benefits.