What Causes Vitamin K Deficiency Bleeding? A Comprehensive Guide

October 29, 2025 •

4 min read

According to the American Academy of Pediatrics, infants who do not receive a prophylactic vitamin K shot are 80 times more likely to develop late vitamin K deficiency bleeding (VKDB). Understanding what causes vitamin K deficiency bleeding is vital for preventing this serious condition, which affects both vulnerable newborns and specific populations of adults.

Quick Summary

Vitamin K deficiency bleeding (VKDB) is caused by factors including inadequate dietary intake, poor fat absorption from underlying medical conditions, long-term antibiotic use, or the effects of certain medications that interfere with vitamin K metabolism.

Key Points

Infants are uniquely vulnerable: Newborns are born with low vitamin K stores and immature gut flora, making them highly susceptible to VKDB without a prophylactic injection.
Fat malabsorption is a key cause in adults: Since vitamin K is fat-soluble, digestive and liver disorders that impair fat absorption are major risk factors for adult deficiency.
Medications can trigger deficiency: Anticoagulants like warfarin and long-term broad-spectrum antibiotics are common culprits that interfere with vitamin K function and synthesis.
Gut bacteria play a role: While less significant than diet for healthy adults, the disruption of gut bacteria by antibiotics can reduce the body's internal production of vitamin K2.
Dietary intake matters, but less so for healthy adults: Inadequate dietary vitamin K is rarely the sole cause of deficiency in otherwise healthy adults, but becomes a factor with severe malnutrition or restrictive diets.
Prevention is crucial: In newborns, prophylaxis with a vitamin K shot is the best preventative measure, while in adults, addressing underlying medical conditions and managing medication is key.

The Essential Role of Vitamin K

Vitamin K is a fat-soluble vitamin critical for the body's natural blood clotting process. Its primary function involves assisting specific enzymes in the liver to activate proteins known as clotting factors. Without sufficient vitamin K, the liver cannot produce enough of these factors, which impairs the body's ability to stop bleeding effectively. This defect in coagulation is the underlying cause of VKDB.

Why are Newborns Prone to VKDB?

Vitamin K deficiency bleeding in newborns is a distinct and serious concern, and it is a medical emergency that can lead to severe bleeding, including life-threatening intracranial hemorrhage. Several physiological factors place infants at a high risk:

Limited placental transfer: Only minimal amounts of vitamin K cross the placenta during pregnancy, meaning newborns have very low vitamin K reserves at birth.
Immature gut flora: A baby's intestinal tract is relatively sterile at birth and lacks the bacteria that produce menaquinones (vitamin K2). It takes time for these gut bacteria to colonize.
Low vitamin K in breast milk: While breast milk is the ideal nutrition, it contains low levels of vitamin K compared to infant formula. Exclusively breastfed infants who do not receive vitamin K prophylaxis are at an increased risk for late VKDB.
Maternal medication use: Certain medications taken by the mother during pregnancy can increase the infant's risk. This includes anticonvulsants (e.g., phenytoin, carbamazepine) and antituberculosis drugs (e.g., rifampin, isoniazid).
Underlying infant conditions: Some congenital or acquired conditions in infants, such as liver disease (e.g., biliary atresia, neonatal hepatitis) or malabsorption issues (e.g., cystic fibrosis), can impair vitamin K absorption and utilization.

What Causes VKDB in Adults?

While less common in healthy adults, VKDB can occur due to various health issues and lifestyle factors. In these cases, the deficiency typically stems from impaired absorption rather than a lack of dietary intake alone.

Medical conditions causing fat malabsorption

Since vitamin K is a fat-soluble vitamin, its absorption relies on the presence of dietary fat and a healthy digestive system. Conditions that disrupt fat absorption can lead to a deficiency:

Biliary tract diseases: Conditions causing a blockage in the bile ducts, like gallstones or cirrhosis, prevent bile salts from reaching the intestine. Bile salts are necessary for fat and fat-soluble vitamin absorption.
Gastrointestinal disorders: Inflammatory bowel diseases like Crohn's disease, celiac disease, and severe chronic diarrhea impair the intestinal lining's ability to absorb nutrients.
Cystic fibrosis: This genetic disorder causes the body to produce thick mucus that can block pancreatic and bile ducts, leading to malabsorption.
Surgical resection: Removal of parts of the small intestine, especially the ileum, can significantly reduce the area available for absorbing nutrients.

Drug-induced vitamin K deficiency

Several types of medications can interfere with vitamin K metabolism or synthesis:

Anticoagulants (warfarin): These 'blood thinners' are designed to inhibit the enzyme responsible for recycling vitamin K in the body, which is how they prevent blood clots.
Prolonged antibiotic use: Long-term or broad-spectrum antibiotic therapy can wipe out beneficial bacteria in the gut. As these bacteria are a source of menaquinones (vitamin K2), this can contribute to deficiency, especially in patients with poor dietary intake.
Other medications: Certain anticonvulsants (phenytoin, barbiturates), salicylates (aspirin in high doses), and cholestyramine (a bile acid sequestrant) have been associated with impaired vitamin K metabolism.

Dietary and lifestyle causes

While dietary deficiency is rare in healthy adults, it can occur in some circumstances:

Severe malnutrition: Conditions like severe alcoholism, eating disorders, or long-term parenteral (IV) nutrition without proper supplementation can lead to insufficient intake.
Extremely low-fat diets: Because vitamin K is fat-soluble, it requires dietary fat for optimal absorption. Very restricted low-fat diets can therefore increase the risk of deficiency.

Comparison of Causes: Infants vs. Adults


Cause	Infants	Adults	Remarks
Inadequate intake/stores	Primary cause, due to low placental transfer and low breast milk content.	Rare cause, unless severe malnutrition or specific diet restrictions are present.	Healthy adults can typically get sufficient vitamin K from food and gut bacteria.
Malabsorption	Can occur due to underlying conditions like liver disease or cystic fibrosis.	Common cause, resulting from diseases like celiac disease, Crohn's, or biliary obstruction.	Requires bile for proper absorption in both populations.
Medications	Induced by drugs taken by the mother (e.g., anticonvulsants) that cross the placenta.	Caused by drugs like warfarin and prolonged use of broad-spectrum antibiotics.	Drug effects vary depending on the specific medication and dosage.
Gut bacteria	Newborns have a sterile gut, leading to low bacterial production of menaquinones.	Antibiotic use can disrupt the gut microbiome, impacting vitamin K2 production.	The contribution of gut bacteria is more significant for menaquinone (K2) synthesis.

Conclusion

Vitamin K deficiency bleeding is a severe condition resulting from the body's inability to produce adequate clotting factors. While it is a critical concern in newborns due to naturally low reserves and maternal factors, in adults, it almost always stems from an underlying medical issue, malabsorption, or medication use rather than a poor diet alone. Identifying and addressing these underlying causes is essential for preventing dangerous and potentially life-threatening bleeding episodes.

For more information on nutrition, consult resources like the Harvard T.H. Chan School of Public Health's The Nutrition Source.

Frequently Asked Questions

Newborns are born with low vitamin K stores due to poor placental transfer. Combined with a sterile gut and low vitamin K content in breast milk, this places them at high risk for bleeding.

Fat malabsorption disorders are the most common cause in adults. These include liver disease (like cirrhosis), cystic fibrosis, celiac disease, and Crohn's disease, all of which interfere with the absorption of fat-soluble vitamins.

Yes, prolonged courses of broad-spectrum antibiotics can disrupt the gut bacteria that produce vitamin K2. This can contribute to a deficiency, especially in individuals with poor dietary intake.

The liver is responsible for producing the clotting factors that depend on vitamin K. Liver diseases, such as cirrhosis or biliary tract obstruction, can impair this function and lead to bleeding complications.

As a fat-soluble vitamin, vitamin K needs dietary fat for proper absorption in the small intestine. A severely restricted low-fat diet can therefore increase the risk of deficiency.

It is rare for diet alone to cause a deficiency in healthy adults because vitamin K is widespread in many foods and gut bacteria also contribute to its production. Severe malnutrition is usually required for a dietary cause.

Warfarin works by blocking the enzyme that recycles vitamin K. This prevents the activation of clotting factors and is the mechanism by which the drug prevents harmful blood clots from forming.