Vitamin K is a fat-soluble micronutrient that is less talked about than other vitamins but performs several important functions in the body. It exists in two forms, phylloquinone (vitamin K1) and menaquinone (vitamin K2). Phylloquinone is the primary form in green leafy vegetables like kale, collard greens, and spinach. Menaquinones can be found in animal and fermented foods and can also be produced by the human body's bacteria.

Vitamin K plays a role in the production of blood clotting and bone-building proteins such as prothrombin and osteocalcin. The vitamin is present throughout the body, including in the liver, heart, brain, pancreas, and bones.

66.9% of Americans are deficient in vitamin K. Deficiencies can cause an increased risk of uncontrolled bleeding, weakened bones and osteoporosis, and a heightened risk of cardiovascular disease.

What is Vitamin K?

Vitamin K is a coenzyme for carboxylase, an enzyme necessary for producing proteins that regulate blood clotting and bone metabolism. It also plays a key role in regulating prothrombin (clotting factor II), a plasma protein directly involved in blood clotting.

Some anticoagulants like warfarin impede vitamin K activity, making it essential for those taking these drugs to maintain consistent vitamin K intake.

Vitamin K is also crucial for activating Matrix Gla protein (MGP), a potent inhibitor of soft tissue calcification, which is a significant reason why vitamin K is important for cardiac health.

Vitamin K is absorbed in the small intestine and transported through the lymphatic capillaries to the liver and other body parts, including the heart, brain, pancreas, and bone. Most of it is metabolized and excreted quickly, resulting in lower blood levels and tissue stores than other fat-soluble vitamins. Although gut bacteria produce vitamin K, it is still unknown how much the body absorbs and utilizes from this source.

What is Vitamin K's Role in The Body?

Vitamin K plays several roles in the human body:

• Bone Health: Vitamin K plays a role in bone metabolism and helps to direct calcium into the bones where it is needed for strength and density. A lack of vitamin K has been linked to an increased risk of osteoporosis, a condition characterized by weak and fragile bones. Some studies have linked higher vitamin K intake to higher bone mineral density and lower risk of fractures. Vitamin K deficiency is also associated with osteopenia, a reduction in bone mineral density that weakens the bones, resulting from a decreased mineral content and a disrupted bone structure.
• Blood Clotting: Vitamin K acts as a coenzyme for the carboxylase enzyme, which is necessary to produce hemostasis proteins. Most vitamin K1 is stored in the liver to synthesize clotting factors. In contrast, K2 vitamins are incorporated into low-density lipoproteins (LDL) and released into the bloodstream. Prothrombin is a key component in blood clotting and a vitamin K-dependent protein in the plasma.
• Heart Health: Vascular calcification is a risk factor for coronary heart disease as it reduces arterial elasticity. Vitamin K-dependent protein matrix Gla-protein (MGP) may play a role in preventing vascular calcification. Inadequate vitamin K status may lead to undercarboxylated MGP, which could increase the risk of coronary heart disease. Observational studies have shown that dietary menaquinone intake is inversely associated with coronary calcification, meaning higher menaquinone intake is linked to a lower risk of coronary heart disease mortality.

How to Test Vitamin K Levels

Vitamin K status is usually not assessed except for those taking anticoagulants or having bleeding disorders. To prevent bleeding, it's crucial to identify and address vitamin K deficiency promptly. Populations with a higher risk of suffering from vitamin K deficiency include individuals with dietary limitations or malnutrition, lipid absorption issues, cancer, kidney disease, newborns, and the elderly. A lack of vitamin K can also affect bone mineralization and contribute to osteoporosis, as vitamin K is needed for the carboxylation of osteocalcin in bones.

Different laboratory tests can be performed to assess vitamin K levels:

• Prothrombin time: this test measures the time it takes for the blood to clot. A deficiency in vitamin K is indicated by an extension of the prothrombin time (excessive bleeding time). The prothrombin time has historically been used to assess vitamin K status. However, it is only considered abnormal if there is a significant decrease of around 50% in prothrombin activity.
• Vitamin K1 and Vitamin K2: The most common method to assess vitamin K levels is to measure the amount of phylloquinone (vitamin K1) in the blood, which indicates the vitamin's availability. A practitioner may also test the levels of vitamin K2 in the blood. However, the evidence is not yet clear on whether K2 is a helpful marker or not.

How to Make Sure You are Getting Enough Vitamin K in Your Diet

Men are advised to consume 120 micrograms daily, while women are recommended to have 90 micrograms daily. Deficiencies can occur in individuals with malabsorption conditions, in those who heavily consume alcohol, or in those taking drugs that disrupt vitamin K metabolism.

A normal diet should provide enough vitamin K for the body. Vitamin K can be found in the following foods:

The Adequate Intakes (AIs) for Vitamin K are:

Both forms of vitamin K can be found in supplement form. While vitamin K1 is more frequently used in single dietary supplements and multivitamins, the natural long-chain menaquinone-7 (MK-7), vitamin K2, has been shown to increase serum levels more effectively.

Summary

Vitamin K is a crucial nutrient that plays a vital role in several aspects of human health. It is essential for blood clotting, bone health, and heart health. For example, it helps the body produce clotting factors, which are proteins responsible for stopping bleeding when we get injured. Without adequate vitamin K, the blood may not clot properly, leading to an increased risk of bleeding and bruising. Vitamin K also helps to direct calcium into the bones, where it is needed for strength and density. A lack of vitamin K has been linked to an increased risk of osteoporosis, a condition characterized by weak and fragile bones. Some studies have suggested that vitamin K may help to reduce the risk of heart disease by improving arterial health and reducing the calcification of the arteries.

Vitamin K is generally best consumed through dietary sources such as leafy greens, broccoli, Brussels sprouts, and fermented dairy products. However, supplementation is also available for those who require additional support. Vitamin K has the potential to reach toxic amounts when supplemented since it is fat-soluble. It can also interfere with blood thinning medications. Therefore supplementation is only recommended at the discretion and recommendation of a knowledgeable healthcare practitioner.