Vitamin K deficiency means the body does not have enough vitamin K to make blood clot normally. This can lead to easy bruising or bleeding, although low intake alone may not cause symptoms. Deficiency is uncommon in healthy adults, but can occur when the body cannot absorb fat well, with certain medicines, or in newborns who have not received vitamin K at birth. Treatment depends on the cause.
What Does Vitamin K Do in the Body?
Vitamin K is a fat-soluble vitamin, meaning it dissolves in fat. The body needs it to produce proteins that help blood clot and stop bleeding after an injury. Vitamin K also supports normal bone health. Two main forms are vitamin K1, found mostly in plant foods, and vitamin K2, found in some animal and fermented foods and produced by certain intestinal bacteria.
According to the Merck Manual Consumer Version, vitamin K deficiency is uncommon in healthy adults because food usually supplies enough of the vitamin and intestinal bacteria produce some vitamin K. However, having a condition that affects absorption or taking certain medicines can increase the risk.
What Causes Vitamin K Deficiency?
Low vitamin K can result from not getting enough through food, difficulty absorbing it, or problems affecting how the body uses it. In adults, poor absorption is often a more important concern than a low intake alone.
- Limited dietary intake: Eating very few vitamin K-rich foods over time may contribute to inadequate intake, particularly when the overall diet is restricted.
- Digestive conditions that affect absorption: Conditions such as celiac disease, cystic fibrosis, and certain forms of inflammatory bowel disease can interfere with the absorption of fat and fat-soluble vitamins.
- Conditions affecting bile flow: Problems involving the bile ducts can reduce the body's ability to absorb dietary fat and vitamin K.
- Digestive surgery: Surgery involving parts of the small intestine or certain weight-loss procedures may reduce nutrient absorption.
- Some medicines: Prolonged antibiotic treatment may reduce vitamin K availability. Orlistat and bile acid-binding medicines, such as cholestyramine, can also interfere with its absorption.
- Warfarin treatment: This medicine interferes with vitamin K's role in blood clotting. Its effect is different from a dietary deficiency, but the medicine and changes in vitamin K intake must be considered together.
The National Institutes of Health (NIH) Office of Dietary Supplements explains that conditions affecting absorption, certain medicines, and changes in vitamin K intake can all be relevant when assessing vitamin K status. People taking medicines that affect vitamin K should review dietary or supplement changes with their healthcare professional rather than making sudden changes themselves.
What Are the Signs of Low Vitamin K?
Vitamin K deficiency mainly affects the body's ability to form blood clots. When a deficiency becomes significant, bleeding may occur more easily or last longer than expected. However, these symptoms can also occur for many other reasons and are not specific to vitamin K deficiency.
- Bruising easily or developing unexplained bruises.
- Frequent nosebleeds or bleeding from the gums.
- Bleeding from small cuts that takes longer than expected to stop.
- Heavier or longer menstrual bleeding than usual.
- Blood in the urine or stool.
- Black, tarry stools, which may indicate bleeding in the digestive tract.
- Bleeding that continues from a wound, surgical incision, or injection site.
According to MedlinePlus, a service of the U.S. National Library of Medicine, people with vitamin K deficiency may be more likely to experience bruising and bleeding. The pattern of symptoms, medical history, medicines, and examination findings help clinicians determine which explanation is most likely.
When should bleeding be assessed urgently?
Seek urgent medical care for bleeding that will not stop, vomiting blood, red blood in the stool or urine, black tarry stools, or substantial unexplained bruising. Heavy bleeding, fainting, or symptoms suggesting significant blood loss require emergency assessment. Do not wait for a vitamin test before seeking help when bleeding is significant.
Why Is Vitamin K Deficiency Different in Newborns?
Newborns naturally have very little vitamin K stored in their bodies. They receive limited amounts before birth, and their intestines initially contain few of the bacteria that can produce it. Breast milk also contains relatively little vitamin K. As a result, newborns are particularly vulnerable to vitamin K deficiency bleeding if they do not receive preventive vitamin K after birth.
The U.S. Centers for Disease Control and Prevention (CDC) explains that vitamin K deficiency bleeding can occur during the first six months of life, sometimes without warning signs before serious bleeding develops. A vitamin K injection shortly after birth is the recommended prevention strategy in the United States.
Parents and caregivers should contact a healthcare professional urgently if a baby develops unexplained bruising, bleeding from the nose or umbilical cord, unusual paleness, or other concerning symptoms. A newborn who has not received the vitamin K injection needs prompt discussion with a pediatric healthcare professional about prevention. A normal-looking baby cannot be assumed to be protected from deficiency-related bleeding.
How Is Vitamin K Deficiency Diagnosed?
A healthcare professional considers symptoms, dietary habits, medical history, digestive conditions, recent procedures, and medicines when evaluating possible vitamin K deficiency. Easy bruising alone does not establish the cause. Other conditions, including liver disease, platelet disorders, and the effects of anticoagulant medicines, can also lead to abnormal bleeding.
Blood tests commonly include measurements of clotting time. The prothrombin time (PT) and international normalized ratio (INR) help show how long blood takes to clot. Vitamin K deficiency can prolong these results, although the findings are not specific to deficiency and may also be affected by medicines or liver problems. In selected cases, a clinician may request a vitamin K blood level.
The MSD Manual Professional Edition describes clotting tests as an important part of evaluating suspected vitamin K deficiency. A healthcare professional interprets the results alongside the clinical history and other possible causes before deciding whether replacement is needed.
A Practical Guide to Getting Enough Vitamin K
Which foods contain vitamin K?
For most people, a varied diet is the simplest way to obtain vitamin K. Leafy green vegetables are especially useful sources of vitamin K1. Other vegetables, some vegetable oils, and selected animal and fermented foods also contribute to intake.
- Green leafy vegetables: Spinach, kale, collard greens, Swiss chard, mustard greens, and lettuce.
- Other vegetables: Broccoli, Brussels sprouts, cabbage, and cauliflower.
- Vegetable oils: Soybean oil and canola oil.
- Other sources: Soybeans, eggs, certain cheeses, meat, and fish.
Because vitamin K is fat-soluble, it is absorbed better when eaten with some fat. For example, adding a little vegetable oil to cooked greens or eating them as part of a balanced meal can help with absorption. People who have a condition that impairs fat absorption may still need medical assessment even when they eat vitamin K-rich foods regularly.
How much vitamin K do people need each day?
Vitamin K needs depend on age and sex. The following are U.S. adequate intake estimates from the NIH Office of Dietary Supplements. They are general dietary reference values, not blood-test targets or proof that an individual has a deficiency.
- Birth to 6 months: 2 micrograms (mcg) per day.
- 7–12 months: 2.5 mcg per day.
- Children aged 1–3 years: 30 mcg per day.
- Children aged 4–8 years: 55 mcg per day.
- Children aged 9–13 years: 60 mcg per day.
- Adolescents aged 14–18 years: 75 mcg per day.
- Adult men aged 19 years and older: 120 mcg per day.
- Adult women aged 19 years and older: 90 mcg per day, including during pregnancy and breastfeeding.
These values are intended to guide intake in generally healthy people. Infants have separate nutritional needs, and their vitamin K injection at birth serves a different purpose from meeting daily dietary needs. Anyone with a diagnosed deficiency or a condition affecting absorption may need an individualized plan.
What practical food changes can help?
Start with regular meals rather than a sudden increase in supplements or large quantities of a single food. Include a leafy green vegetable or another vitamin K source in meals throughout the week, rotate among different vegetables, and maintain an overall balanced diet. People who avoid particular foods can discuss suitable alternatives with a dietitian or healthcare professional.
Food changes are useful for maintaining adequate intake, but they may not correct a confirmed deficiency when poor absorption or another medical condition is involved. A clinician can help identify the underlying problem and decide whether dietary changes alone are appropriate.
Should You Take Vitamin K Supplements?
Vitamin K supplements are available in different forms, including vitamin K1 and vitamin K2. They may be appropriate when a healthcare professional identifies a deficiency or a specific need. The choice of product, dose, and route depends on the person's condition, medicines, and ability to absorb the vitamin.
Do not start high-dose vitamin K supplements to treat unexplained bruising or bleeding without medical guidance. Unnecessary supplementation may complicate medicine management, particularly for people taking warfarin. When a deficiency is confirmed, treatment may involve vitamin K by mouth or by injection, depending on the cause and the clinical situation.
What if you take warfarin?
Warfarin reduces the activity of vitamin K to help prevent harmful blood clots. A sudden change in vitamin K intake can alter how warfarin works. People taking it generally need a consistent amount of vitamin K in their diet rather than avoiding leafy green vegetables altogether.
Keep your intake reasonably consistent from day to day, and tell your anticoagulation team or prescribing clinician before making major dietary changes or starting supplements. Your clinician may need to check your INR more closely after a significant change. Do not adjust your warfarin dose or take vitamin K to counteract its effects unless instructed by your healthcare professional.
What Is the Best Next Step if Low Vitamin K Is Suspected?
If you are concerned about your intake, review your usual eating pattern and include a variety of vitamin K-rich foods where appropriate. If you have persistent unexplained bruising, unusual bleeding, a digestive condition that affects absorption, or a history of relevant surgery, arrange a medical evaluation. Bring a list of medicines and supplements to the appointment so potential interactions can be reviewed.
If testing confirms deficiency, the priority is to correct the low vitamin K and address the reason it developed. Improving dietary intake may be sufficient for some people, while others need prescribed replacement or further investigation. With the right evaluation and treatment, vitamin K deficiency can often be managed effectively.