What vitamin helps blood to clot and control bleeding?

January 1, 2026 •

4 min read

A single dose of vitamin K is recommended for all newborns to prevent life-threatening bleeding disorders. This critical fat-soluble nutrient is the primary vitamin that helps blood to clot and control bleeding throughout life, playing a vital role in hemostasis.

Quick Summary

Vitamin K is a fat-soluble nutrient crucial for producing proteins required for blood clotting. Found in leafy greens and produced by gut bacteria, a deficiency can cause excessive bleeding.

Key Points

Vitamin K is the clotting vitamin: It is a fat-soluble nutrient essential for producing the proteins required for blood coagulation.
Two main forms exist: Vitamin K1 (phylloquinone) is found in plants like leafy greens, and Vitamin K2 (menaquinone) is produced by gut bacteria and found in fermented foods.
Deficiency leads to bleeding: Insufficient vitamin K impairs clotting, leading to excessive bleeding and easy bruising.
Newborns are at high risk: Because they are born with low vitamin K stores, newborns receive a prophylactic injection to prevent life-threatening bleeding.
Dietary sources are key: A diet rich in foods like kale, spinach, and broccoli provides adequate vitamin K for most healthy adults.
Medication interactions are a risk: People on blood thinners like warfarin must maintain a consistent vitamin K intake to ensure the medication works as intended.

The Essential Role of Vitamin K in Coagulation

Vitamin K is a fat-soluble vitamin best known for its critical function in blood coagulation, or clotting. Without adequate vitamin K, the body cannot produce the specific proteins needed to form clots, a process that is essential for stopping wounds from bleeding and for healing. This vital process, known as hemostasis, protects us from excessive blood loss from even minor injuries. The importance of vitamin K is demonstrated by the standard practice of administering a vitamin K injection to all newborns, as they are born with very low levels and are at risk for life-threatening bleeding disorders.

The Vitamin K Cycle: How It Works

To be active, vitamin K undergoes a metabolic process known as the vitamin K cycle. Within the liver, vitamin K acts as a co-enzyme for an enzyme called gamma-glutamyl carboxylase. This enzyme activates several key coagulation factors—including factors II (prothrombin), VII, IX, and X—by adding carboxylic acid groups to their glutamate residues. This modification allows these clotting factors to bind to calcium ions, which is a crucial step in the coagulation cascade that ultimately leads to the formation of a fibrin clot. A deficiency interrupts this cycle, resulting in the production of inactive clotting factors that cannot bind calcium and, consequently, impaired blood clotting. This is also the mechanism by which the anticoagulant medication warfarin works, by blocking the action of an enzyme in the vitamin K cycle, effectively inhibiting clotting.

Forms of Vitamin K: K1 vs. K2

Vitamin K exists in two primary natural forms, each with different sources and functions in the body.

Vitamin K1 (Phylloquinone):

Found primarily in green leafy vegetables, including spinach, kale, and broccoli.
Directly involved in the liver's production of blood-clotting factors.
Absorbed in the small intestine along with other dietary fats.

Vitamin K2 (Menaquinone):

Produced by bacteria in the lower intestinal tract.
Also found in fermented foods like natto, and in some animal products, such as cheeses and eggs.
Plays a significant role in bone and cardiovascular health, including helping to prevent arterial calcification.

Comparison of Vitamin K1 and Vitamin K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Source	Green leafy plants	Gut bacteria, fermented foods, animal products
Main Function	Primarily blood clotting in the liver	Bone health and cardiovascular health
Absorption	Absorbed from plant foods in the small intestine	Absorbed from gut bacteria and foods; longer half-life
Stability	Relatively stable during cooking	Varies depending on the specific menaquinone (MK)

Dietary Sources of Vitamin K

For most adults, maintaining an adequate intake of vitamin K is achievable through a balanced and varied diet. The most common form, K1, is abundant in many vegetables. List of key food sources:

Kale
Spinach
Collard greens
Turnip greens
Brussels sprouts
Broccoli
Lettuce, especially romaine
Cabbage
Vegetable oils, particularly canola and soybean
Natto (fermented soybeans)
Meat, eggs, and dairy (smaller amounts, primarily K2)

What Causes a Vitamin K Deficiency?

While clinically significant vitamin K deficiency is rare in healthy adults, certain conditions and medications can increase the risk. The most susceptible groups include newborns, who are born with low stores, and individuals with certain health issues. Risk factors for a deficiency include:

Newborns: Limited vitamin K transfer across the placenta and low levels in breast milk increase risk, which is why prophylactic injections are standard practice.
Malabsorption Disorders: Conditions like celiac disease, cystic fibrosis, and ulcerative colitis can impair fat absorption, reducing vitamin K uptake.
Liver Disease: Since the liver produces clotting factors, severe liver disease, such as cirrhosis, can affect vitamin K utilization.
Prolonged Antibiotic Use: Certain antibiotics can destroy the gut bacteria that produce vitamin K2.
Medications: Drugs like bile acid sequestrants and the weight-loss drug orlistat can interfere with vitamin K absorption.

Risks of Deficiency and Toxicity

The most significant risk of vitamin K deficiency is excessive or uncontrolled bleeding, which can manifest as easy bruising, nosebleeds, blood in the urine or stool, or heavy menstrual bleeding. In severe cases, it can lead to internal hemorrhages, especially in the brain, which can be life-threatening. In infants, severe bleeding, particularly into the brain, is a serious complication of deficiency.

Conversely, toxicity from dietary or supplemental vitamin K1 and K2 is extremely rare. There is no established tolerable upper intake level (UL) for these forms. However, a synthetic form known as vitamin K3 (menadione) can be toxic and is no longer used in supplements. An allergic reaction is possible with supplements, particularly with intravenous administration of K1.

Recommended Dietary Intake

The National Academy of Science Food and Nutrition Board provides Adequate Intake (AI) recommendations for vitamin K. For adults, the daily AI is 120 micrograms ($μg$) for men and 90 $μg$ for women. It is important to note that individuals on blood-thinning medication like warfarin must maintain a consistent daily intake of vitamin K from food, as fluctuations can affect the medication's efficacy.

Conclusion

Vitamin K is an indispensable fat-soluble vitamin that plays a central role in blood coagulation, effectively helping blood to clot and controlling bleeding. By enabling the production of key clotting factors, it provides a crucial defense mechanism against excessive blood loss. Ensuring sufficient intake through a diet rich in leafy greens and other sources is vital for adults, while newborns require prophylactic administration to mitigate the high risk of deficiency. Maintaining awareness of dietary sources and potential deficiency risks, especially for individuals with malabsorption issues or those taking certain medications, is essential for promoting overall health and preventing dangerous bleeding complications.

For more in-depth information, you can consult the NIH Office of Dietary Supplements fact sheet on Vitamin K.

Frequently Asked Questions

Newborns have low vitamin K levels at birth because it does not cross the placenta easily and breast milk contains only small amounts. A vitamin K shot is given shortly after birth to prevent a serious bleeding disorder known as Vitamin K Deficiency Bleeding (VKDB).

While rare in healthy adults, a deficiency can cause symptoms such as easy bruising, nosebleeds, bleeding gums, blood in the urine or stool, and excessive bleeding from wounds. In severe cases, internal bleeding may occur.

Toxicity from naturally occurring Vitamin K1 and K2 is extremely rare, and no upper intake limit has been established. However, a synthetic form, menadione (K3), can be toxic and is not used in supplements.

Warfarin works by blocking the enzyme that activates vitamin K, which inhibits the production of clotting factors. Individuals on warfarin must maintain a consistent daily intake of vitamin K to avoid dangerous fluctuations in its effect.

Excellent food sources include green leafy vegetables like kale, spinach, and turnip greens, as well as broccoli, Brussels sprouts, and fermented foods like natto.

Bacteria in the large intestine can synthesize vitamin K2 (menaquinone). While this contributes to overall intake, most experts agree that dietary intake, particularly of K1 from plants, is essential to meet the body's needs.

Yes, vitamin K is also involved in producing proteins necessary for healthy bones. Some studies have linked low vitamin K levels to lower bone mineral density and an increased risk of hip fractures.

Prolonged use of antibiotics, especially certain types like cephalosporins, can destroy the vitamin K-producing bacteria in the gut and potentially lead to a deficiency.