What Does a Vitamin K Deficiency Cause? Symptoms, Risks, and Prevention

December 26, 2025 •

4 min read

Affecting blood clotting, bone health, and heart function, a vitamin K deficiency can cause a range of serious health problems if left untreated. While uncommon in healthy adults, it poses a significant risk to newborns and individuals with certain medical conditions.

Quick Summary

A lack of vitamin K impairs blood clotting, leading to easy bruising and excessive bleeding. It can also weaken bones, increasing the risk of osteoporosis, and may contribute to cardiovascular disease. Infants are particularly vulnerable to life-threatening bleeding without proper vitamin K prophylaxis at birth. The risk is also elevated in adults with malabsorption disorders or those on specific medications.

Key Points

Blood Clotting Problems: A vitamin K deficiency impairs blood clotting factors, leading to excessive bleeding and easy bruising.
Bone Weakening: Inadequate vitamin K interferes with bone mineralization, potentially causing osteopenia and osteoporosis.
Risks for Newborns: Infants are highly susceptible to life-threatening Vitamin K Deficiency Bleeding (VKDB), which can include intracranial hemorrhage.
Cardiovascular Disease: A lack of vitamin K2 can lead to vascular calcification, increasing the risk of heart disease and arterial stiffness.
At-Risk Adults: Individuals with malabsorption disorders, liver disease, or those taking certain medications are at higher risk for deficiency.
Prevention is Possible: A balanced diet rich in leafy greens and fermented foods typically provides enough vitamin K for healthy adults.
Diagnosis by Doctors: Medical professionals can diagnose deficiency through blood clotting tests and treat it with dietary changes or supplements.

Impaired Blood Clotting and Hemorrhage

The most well-known and immediate consequence of a vitamin K deficiency is impaired blood clotting, also known as coagulopathy. Vitamin K is a vital cofactor for the activation of several proteins (factors II, VII, IX, and X) that are essential for the coagulation cascade. Without sufficient vitamin K, these proteins cannot mature and function correctly, leading to delayed or ineffective clot formation. This can manifest in several bleeding-related symptoms, both minor and severe.

Common Symptoms of Impaired Clotting

Easy Bruising: Minor bumps or injuries can lead to large, purplish bruises on the skin due to easy bleeding into the skin.
Nosebleeds: Frequent and hard-to-stop nosebleeds are a classic sign of poor clotting function.
Bleeding from Wounds: Cuts or incisions may bleed excessively and for a longer duration than normal.
Internal Bleeding: More serious cases can involve bleeding in the stomach, intestines, or gums. Blood may appear in the urine or stool, sometimes presenting as tarry-black stool.
Heavy Menstrual Bleeding: Women may experience abnormally heavy menstrual periods.

Weakened Bones and Osteoporosis

Beyond its role in coagulation, vitamin K is also crucial for bone metabolism. It plays a key part in activating osteocalcin, a protein produced by osteoblasts that helps bind calcium into the bone matrix. A deficiency reduces the carboxylation of osteocalcin, hindering proper bone mineralization.

Over time, this can lead to:

Osteopenia: A condition characterized by lower-than-normal bone mineral density, which is a precursor to osteoporosis.
Osteoporosis: Severely reduced bone density, making bones weak and brittle and increasing the risk of fractures.

Risks for Vulnerable Populations: Infants and Adults

While uncommon in the average adult, a vitamin K deficiency is a critical concern for newborns and certain at-risk adults due to different physiological reasons.

Vitamin K Deficiency in Newborns

Infants are born with very low levels of vitamin K because only a small amount crosses the placenta, and breast milk contains limited quantities. Without a prophylactic injection at birth, they are susceptible to Vitamin K Deficiency Bleeding (VKDB), also known as hemorrhagic disease of the newborn. This can occur as early, classic, or late-onset bleeding, with late-onset VKDB often causing life-threatening intracranial hemorrhage (bleeding in the brain).

At-Risk Adults

Adults typically get enough vitamin K from their diet and gut bacteria. However, certain conditions and medications increase the risk of deficiency significantly.

Risk Factors and Causes in Adults:

Malabsorption Disorders: Conditions like celiac disease, cystic fibrosis, and Crohn's disease interfere with fat absorption, thereby limiting the absorption of fat-soluble vitamin K.
Liver Disease: Since the liver produces the vitamin K-dependent clotting factors, liver disorders increase the risk of bleeding.
Antibiotics: Extended courses of antibiotics can wipe out the gut bacteria that produce some of our vitamin K.
Blood Thinners: Medications like warfarin work by blocking the effects of vitamin K, which requires careful monitoring.

Comparison of Vitamin K1 and K2 Functions

Vitamin K exists in two main forms: K1 (phylloquinone) and K2 (menaquinones). While both are important for health, they have distinct roles that are compromised during a deficiency.


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)
Primary Source	Green leafy vegetables like kale, spinach, and broccoli.	Fermented foods, some cheeses, meat, and eggs. Also produced by gut bacteria.
Main Function	Acts primarily in the liver to activate proteins needed for blood coagulation.	Functions primarily in extrahepatic tissues, activating proteins involved in bone metabolism and cardiovascular health.
Deficiency Effect	Leads to impaired blood clotting and excessive bleeding.	Impacts bone mineralization (osteocalcin) and contributes to vascular calcification (Matrix Gla Protein).

The Link to Cardiovascular Health

Emerging research suggests a link between vitamin K deficiency and a heightened risk of cardiovascular disease. Vitamin K2 is particularly relevant here, as it activates Matrix Gla Protein (MGP), a potent inhibitor of soft tissue and arterial calcification. Without enough vitamin K2, MGP remains inactive, allowing calcium to deposit in blood vessels and potentially leading to arterial stiffness and clogged arteries.

Conclusion

In summary, a vitamin K deficiency causes a range of health issues, from the obvious signs of excessive bleeding and easy bruising to less apparent problems with bone density and cardiovascular health. While most adults are not at risk, special care is needed for newborns and individuals with malabsorption issues, liver disease, or those taking specific medications. Recognition of the signs and addressing the underlying cause with dietary changes or supplementation is critical for preventing serious complications. Maintaining adequate vitamin K intake, especially from sources rich in both K1 and K2, is a simple yet effective strategy for overall well-being. For more detailed information on vitamin K, consult the National Institutes of Health (NIH) website (https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/).

Prevention and Dietary Sources

Prevention is key, and maintaining a balanced diet is the best defense against vitamin K deficiency for healthy individuals. Since the body stores very little vitamin K, regular dietary intake is essential.

Food Sources for Vitamin K:

Vitamin K1 (Phylloquinone): Found in high concentrations in green leafy vegetables such as kale, spinach, collard greens, turnip greens, and broccoli.
Vitamin K2 (Menaquinones): Obtained from animal products like meat, eggs, and cheese, as well as fermented foods like natto.

Individuals with malabsorption disorders or those on specific medications should work with a healthcare provider to ensure adequate vitamin K status through diet or supplements.

Diagnosis and Treatment

Diagnosis of a vitamin K deficiency usually involves a medical evaluation and blood tests to measure clotting time, such as a prothrombin time (PT) test. In severe cases, tests may also look for specific proteins produced when vitamin K is absent or ineffective.

Treatment depends on the severity and cause of the deficiency:

Dietary Adjustments: Milder cases can often be corrected by increasing intake of vitamin K-rich foods.
Supplements: Oral or injectable vitamin K supplements may be prescribed by a doctor.
Newborn Prophylaxis: A single intramuscular vitamin K injection is standard practice for newborns to prevent VKDB.

Frequently Asked Questions

The primary and most significant symptom of a vitamin K deficiency is excessive bleeding or hemorrhage, which results from impaired blood clotting due to low levels of this essential vitamin.

Newborns with a vitamin K deficiency can develop a condition called Vitamin K Deficiency Bleeding (VKDB). This can lead to serious internal bleeding, especially in the brain, and is prevented by a standard vitamin K injection at birth.

Yes, vitamin K is important for bone metabolism and mineralization. A deficiency can reduce bone mineral density, leading to conditions like osteopenia and osteoporosis over time.

While rare in healthy adults, those with malabsorption disorders (like celiac disease or cystic fibrosis), liver disease, or who are taking specific medications (such as warfarin or certain antibiotics) are at higher risk.

Vitamin K2, a form of the vitamin, helps activate proteins that prevent vascular calcification, which is the buildup of calcium in arteries. A deficiency may therefore increase the risk of cardiovascular disease.

Yes, blood thinners like warfarin are designed to block the effects of vitamin K to prevent clotting. People on these medications require careful monitoring and consistent vitamin K intake.

Good sources of vitamin K1 include leafy green vegetables like kale and spinach, while vitamin K2 can be found in fermented foods, eggs, and some cheeses.

Doctors can diagnose a vitamin K deficiency using blood tests to measure the blood's clotting time, such as a prothrombin time (PT) test, and by assessing an individual's risk factors and symptoms.