What Happens If Vitamin K Is Low? Uncontrolled Bleeding and Beyond

October 31, 2025 •

2 min read

According to the Centers for Disease Control and Prevention (CDC), newborns who do not receive a vitamin K shot are 80 times more likely to develop late vitamin K deficiency bleeding. Knowing what happens if vitamin K is low is vital for all age groups, as it can affect everything from blood coagulation to long-term bone density.

Quick Summary

A lack of vitamin K can severely impair the body's blood clotting ability, leading to uncontrolled bleeding and easy bruising. Consequences range from mild symptoms to life-threatening internal hemorrhaging, especially in newborns, and can impact long-term bone and heart health. Deficiency is often linked to malabsorption issues, certain medications, or inadequate dietary intake.

Key Points

Impaired Blood Clotting: The most critical effect of low vitamin K is poor blood clotting, leading to excessive bleeding and easy bruising.
Risk for Newborns: Infants are highly susceptible to Vitamin K Deficiency Bleeding (VKDB), a serious, potentially fatal condition, which is why a prophylactic injection is standard at birth.
Compromised Bone Health: A long-term deficiency can weaken bones by preventing the proper activation of bone-mineralizing proteins like osteocalcin, increasing osteoporosis risk.
Increased Cardiovascular Risk: Low vitamin K, particularly K2, is linked to an increased risk of arterial calcification and heart disease due to its role in regulating calcium.
Diagnosis is Blood-Based: Vitamin K deficiency is diagnosed using blood tests like Prothrombin Time (PT) and INR, which measure blood clotting speed.
Treatable with Supplements: Treatment involves vitamin K supplements, given orally or via injection, depending on the severity of the deficiency.
Causes are Varied: Risk factors include malabsorption issues, certain medications (like warfarin and some antibiotics), liver disease, and inadequate dietary intake.

The Critical Role of Vitamin K

Vitamin K is a fat-soluble vitamin essential for several vital bodily functions, including blood clotting and bone metabolism. There are two main naturally occurring forms: vitamin K1 (phylloquinone), found primarily in plant foods like leafy greens, and vitamin K2 (menaquinone), produced by gut bacteria and found in some animal products and fermented foods. When vitamin K levels drop, the body cannot properly produce the proteins required for coagulation and other processes, leading to a cascade of health problems.

Primary Consequences: Impaired Blood Clotting

The most immediate and dangerous consequence of a vitamin K deficiency is impaired blood clotting. Without enough vitamin K, the body cannot form clots properly, leading to excessive bleeding. Symptoms include easy bruising and excessive bleeding from minor injuries. Severe cases can result in life-threatening hemorrhage.

Beyond Coagulation: Impact on Bone and Heart Health

Vitamin K is also crucial for healthy bones and cardiovascular function.

Bone Health: Deficiency can lead to low bone mineral density and potentially osteoporosis.
Cardiovascular Health: Low levels may contribute to arterial stiffness and increase the risk of cardiovascular disease.

Special Vulnerability: Vitamin K Deficiency in Newborns

Newborns are highly susceptible to Vitamin K Deficiency Bleeding (VKDB). VKDB has three forms: early, classical, and late-onset, the latter being the most dangerous and often involving severe bleeding. A prophylactic vitamin K injection at birth is standard to prevent VKDB.

Causes and Risk Factors for Low Vitamin K Levels

Risk factors include malabsorption disorders, certain medications (antibiotics, warfarin), inadequate diet, and liver disease.

A Comparison of Vitamin K1 and K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinones)
Primary Source	Plant-based foods, especially green leafy vegetables	Animal products (meat, eggs, cheese) and fermented foods (natto)
Production	Synthesized by plants for photosynthesis	Synthesized by bacteria in the gut; also occurs in fermented foods
Absorption	Absorbed in the small intestine; absorption improved with dietary fat	Absorbed more readily than K1, especially the MK-7 subtype
Storage Location	Primarily stored in the liver, also in the pancreas and heart	Concentrates in the brain, kidneys, and bone
Primary Function	Essential for blood coagulation (clotting)	More involved in bone mineralization and cardiovascular health

Diagnosis and Treatment Options

Diagnosis involves evaluating symptoms, risk factors, and blood tests like Prothrombin Time (PT), INR, and PIVKA-II.

Treatment includes vitamin K supplementation, addressing underlying conditions, managing medications like warfarin, and newborn prophylaxis. In severe bleeding cases, fresh frozen plasma may be needed {Link: Medscape emedicine.medscape.com/article/126354-treatment}.

Conclusion

Low vitamin K can lead to severe bleeding and long-term health issues like osteoporosis and increased cardiovascular risk. Newborns and individuals with certain conditions or on specific medications are at higher risk. Maintaining adequate intake and newborn injection are key. Consult a healthcare provider for concerns {Link: Medical News Today www.medicalnewstoday.com/articles/219867}.

Frequently Asked Questions

The primary sign of a vitamin K deficiency is excessive bleeding or easy bruising, which occurs because the body cannot produce enough of the proteins needed for proper blood clotting.

Newborns are at high risk because very little vitamin K is passed to them through the placenta, breast milk contains low levels of the vitamin, and their gut bacteria (which produce K2) have not yet developed.

Yes, a long-term deficiency can contribute to bone problems such as osteopenia and osteoporosis. Vitamin K is necessary to activate osteocalcin, a protein that helps bind calcium to the bone matrix.

Conditions that cause poor fat absorption, such as cystic fibrosis, celiac disease, and Crohn's disease, can lead to vitamin K deficiency. Liver disease and obstructions of the biliary tract can also impact vitamin K levels.

Good sources of vitamin K1 include leafy greens like kale, spinach, and broccoli. Foods rich in vitamin K2 include fermented foods like natto, as well as eggs, cheese, and meat.

Treatment for vitamin K deficiency involves administering vitamin K supplements, either orally or via injection, depending on the severity and cause. In severe bleeding cases, fresh frozen plasma may also be given.

Yes. Even if you eat a diet rich in vitamin K, a deficiency can occur due to an underlying health condition that impairs fat absorption or liver function, or due to taking medications that interfere with vitamin K metabolism.