How do I know if my vitamin K is low?

October 13, 2025 •

5 min read

While true vitamin K deficiency is rare in healthy adults, it can lead to serious health issues, primarily affecting blood clotting. Knowing the warning signs is crucial for identifying risk factors and understanding how do I know if my vitamin K is low?

Quick Summary

A vitamin K deficiency can manifest as uncontrolled or excessive bleeding and unexplained bruising. Risk factors include certain medications, malabsorption issues, and liver disease. A medical diagnosis relies on blood tests that measure blood clotting time and rule out other potential causes.

Key Points

Excessive Bleeding: A primary indicator is bleeding that is unusually heavy or prolonged, including nosebleeds, bleeding gums, or heavy menstrual flow.
Easy Bruising: Unexplained and frequent bruising, or bruises that are larger than expected from a minor injury, can signal a deficiency.
Gastrointestinal Distress: Tar-like stools or bloody vomit are red flags for internal gastrointestinal bleeding, which is a severe symptom.
Risk Factors are Key: Individuals with malabsorption disorders, liver disease, or who take certain medications (like warfarin or long-term antibiotics) are at higher risk.
Professional Diagnosis: Only a healthcare professional can confirm a deficiency using specific blood tests like Prothrombin Time (PT) and International Normalized Ratio (INR).
Infant-Specific Symptoms: For newborns, signs can include bleeding around the belly button or excessive bruising, which necessitates immediate medical care.

Understanding Vitamin K and Its Functions

Vitamin K is a crucial fat-soluble nutrient, known primarily for its essential role in the production of proteins needed for blood clotting (coagulation). Without sufficient vitamin K, the liver cannot produce these clotting factors, which can lead to uncontrolled bleeding and other health problems. Beyond its function in hemostasis, vitamin K is also vital for bone metabolism, helping to build and maintain healthy, strong bones.

There are two main forms of vitamin K: K1 (phylloquinone) and K2 (menaquinone). Vitamin K1 comes primarily from plant sources, particularly leafy green vegetables, while vitamin K2 is found in some animal products and fermented foods and is also produced by bacteria in the gut. A balanced diet typically provides sufficient vitamin K, but certain conditions or lifestyle factors can interfere with its absorption and utilization, potentially leading to a deficiency.

Key Symptoms of Vitamin K Deficiency

The primary symptom of a vitamin K deficiency is abnormal or excessive bleeding, due to the impaired ability of the blood to clot effectively. In adults, this can manifest in several ways:

Signs in Adults

Easy bruising: Noticing bruises appearing with minimal or no apparent injury is a common indicator.
Excessive bleeding: Bleeding that lasts longer than normal from wounds, cuts, or injection sites.
Nosebleeds or bleeding gums: Frequent or prolonged bleeding from the nose or gums can be a symptom.
Heavy menstrual bleeding: In women, an unusually heavy menstrual period (menorrhagia) may be a sign.
Blood in stool or urine: Stool that appears dark and tarry or bright red blood in urine can indicate internal bleeding.
Small blood clots under fingernails: These tiny blood clots, known as splinter hemorrhages, can be a sign of a deficiency.

Signs in Infants and Newborns

Vitamin K deficiency is a more significant concern in newborns, a condition called Vitamin K Deficiency Bleeding (VKDB). Signs to watch for include:

Bleeding: This can occur from the umbilical cord, nose, mouth, circumcision site, or in the gastrointestinal tract.
Jaundice: A yellowing of the skin or eyes, especially if it appears after the first two weeks of life.
Bruising: Bruises that appear on the head or face.
Lethargy or irritability: Unusual sleepiness or extreme irritability can signal a more serious underlying issue, such as intracranial hemorrhage.

Who is at Risk for Vitamin K Deficiency?

While uncommon in healthy adults, certain individuals are at a higher risk of developing a vitamin K deficiency. These risk factors typically relate to issues with absorption, metabolism, or dietary intake.

Malabsorption disorders: Conditions that affect the body's ability to absorb fat-soluble vitamins, such as celiac disease, cystic fibrosis, inflammatory bowel disease, or chronic diarrhea.
Liver disease: The liver is responsible for producing vitamin K-dependent proteins. Impaired liver function can reduce the production of these clotting factors, increasing bleeding risk.
Medication use: Long-term use of certain antibiotics can wipe out the gut bacteria that produce vitamin K2. The blood-thinning drug warfarin works by interfering with vitamin K metabolism, requiring careful monitoring.
Newborns: Infants are born with very low levels of vitamin K because only small amounts cross the placenta. This, combined with low levels in breast milk and a sterile gut initially, puts them at risk for VKDB unless they receive a prophylactic vitamin K shot after birth.
Poor diet: A diet consistently low in fat or vitamin K-rich foods can contribute to a deficiency, though this is less common.

How Vitamin K Deficiency is Diagnosed

If a doctor suspects a vitamin K deficiency based on your symptoms and risk factors, they will likely order blood tests to measure the blood's clotting ability.

Diagnostic Blood Tests

Prothrombin Time (PT) and International Normalized Ratio (INR): The primary diagnostic tools are blood tests that measure how long it takes for your blood to clot. A prolonged PT and elevated INR are indicators of a potential vitamin K deficiency. If your INR is too high, it means your blood is clotting too slowly.
Vitamin K response test: This test is often used to confirm the diagnosis. A small dose of vitamin K is administered, and the PT/INR is re-evaluated. If the clotting time returns to a normal range, it confirms that a vitamin K deficiency was the cause.

Dietary Sources and Management

For those at risk or diagnosed with a mild deficiency, increasing dietary intake of vitamin K is often the first step. Here are some of the best food sources:

Leafy greens: Spinach, kale, Swiss chard, mustard greens, and collard greens are excellent sources of Vitamin K1.
Cruciferous vegetables: Broccoli, Brussels sprouts, and cabbage also contain significant amounts.
Vegetable oils: Soybean and canola oil are good sources.
Fermented foods: Natto (a Japanese fermented soybean food) is a rich source of Vitamin K2.
Animal products: Liver, meat, and eggs contain smaller amounts, particularly of Vitamin K2.

A Comparison of Vitamin K Forms


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Source	Plant-based foods (leafy greens, vegetables)	Synthesized by gut bacteria; found in animal products and fermented foods
Key Function	Primarily involved in blood clotting	Important for bone metabolism and cardiovascular health
Absorption	Primarily absorbed in the small intestine	Also absorbed in the small intestine, with some produced in the large intestine
Dietary Intake	Most common form in Western diets	Found in smaller quantities in most Western diets, unless consuming specific fermented foods

Conclusion: When to See a Doctor

Understanding how do I know if my vitamin K is low? starts with recognizing the signs of uncontrolled bleeding and easy bruising. While adult deficiency is not common, it is a serious issue that requires medical attention. Infants, especially those who are breastfed and have not received a prophylactic injection, are particularly vulnerable. If you experience persistent bleeding, unexplained bruising, or have a condition that puts you at risk, it is crucial to consult a healthcare provider for proper diagnosis and management. Timely intervention, which may involve dietary adjustments or supplements, can prevent serious complications related to improper blood clotting and bone health.

For more information on the dietary requirements and benefits of vitamin K, the National Institutes of Health (NIH) Office of Dietary Supplements provides reliable resources. National Institutes of Health (NIH) Office of Dietary Supplements

Frequently Asked Questions

The main sign of a vitamin K deficiency in adults is abnormal bleeding and easy bruising. This can manifest as prolonged bleeding from minor cuts, nosebleeds, bleeding gums, or very heavy menstrual periods.

Yes, newborns are at a higher risk of vitamin K deficiency because they are born with low levels, and breast milk has a low vitamin K content. This is why they are typically given a prophylactic vitamin K injection at birth to prevent a condition known as Vitamin K Deficiency Bleeding (VKDB).

A doctor confirms a vitamin K deficiency with a blood test called a Prothrombin Time (PT) and International Normalized Ratio (INR). These tests measure how quickly the blood clots. A prolonged PT and elevated INR suggest a deficiency.

Yes, certain medications can cause a deficiency. Long-term use of broad-spectrum antibiotics can kill the bacteria in the gut that produce Vitamin K2. Additionally, blood-thinning medications like warfarin intentionally interfere with vitamin K's blood-clotting action.

Excellent food sources of vitamin K include green leafy vegetables like kale, spinach, and collard greens (K1), as well as fermented foods like natto, and certain animal products (K2).

A vitamin K deficiency from dietary intake alone is rare in healthy adults because the vitamin is widely available in many foods, and gut bacteria produce some K2. However, it can be a factor in individuals with very poor nutrition or those on very low-fat diets.

Conditions that impair fat absorption, such as celiac disease, cystic fibrosis, and inflammatory bowel disease, can reduce the absorption of vitamin K, as it is a fat-soluble vitamin.