Vitamin K is important for blood clotting, bone health, and more. The main symptom of a vitamin K deficiency is excessive bleeding caused by an inability to form blood clots.
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If a person is taking a blood thinner, such as warfarin, it is important that they get the same amount of vitamin K every day.
In this article, we look at the function of vitamin K in the body, as well as the symptoms and treatments for a vitamin K deficiency.
Vitamin K comes in two forms:
- vitamin K1, or phylloquinone, which occurs in leafy green vegetables such as spinach and kale.
- vitamin K2 or menaquinone, which occurs in animal-based foods, including butter and egg yolks, and fermented foods, such as kefir. The intestine also creates some of this vitamin.
Both vitamin K1 and vitamin K2 produce proteins that help the blood clot. Blood clotting or coagulation prevents excessive bleeding internally and externally.
If a person has a vitamin K deficiency, that means the person’s body cannot produce enough of these proteins, increasing the risk of excessive bleeding.
Most adults obtain an adequate supply of vitamin K through the foods they eat and through what their body naturally produces.
Certain medications and medical conditions can reduce vitamin K production and inhibit absorption, meaning adults can become deficient.
Vitamin K deficiency is much more likely to occur in infants. When it does, it is known as vitamin K deficiency bleeding or VKDB.
Adults are at an increased risk of vitamin K deficiency and the associated symptoms if they:
- take blood thinners, or anticoagulants, which prevent blood clots but inhibit vitamin K activation
- take antibiotics that interfere with vitamin K production and absorption
- do not get enough vitamin K from the foods they eat
- take extremely high doses of vitamin A or E
Some medical conditions can make vitamin K deficiency more likely to develop, such as conditions where the body is less able to absorb fat. This is known as fat malabsorption.
Conditions associated with fat malabsorption include:
- celiac disease
- cystic fibrosis
- an intestinal or biliary tract (liver, gallbladder, and bile ducts) disorder
- having had part of the intestine removed, such as during bariatric surgery
There are several reasons why newborn babies are more prone to vitamin K deficiency:
- breast milk is low in vitamin K
- vitamin K does not transfer well from the placenta to the baby
- a newborn’s liver is unable to use vitamin K efficiently
- a newborn’s gut cannot produce vitamin K2 in the first few days of life
- 120 micrograms (mcg) for males
- 90 mcg for females
Foods that are high in vitamin K include:
- green leafy vegetables, including spinach, kale, lettuce, and broccoli
- vegetable oils
- some fruits, such as blueberries and figs
- meat, including liver
- green tea
People can also take vitamin K supplements. It is best to talk to a doctor before taking these as they could interfere with existing medications.
There are several symptoms associated with vitamin K deficiency. The main symptom is excessive bleeding.
Excessive bleeding may not be immediately evident, as it might only occur if the person gets a cut.
Additional signs of excessive bleeding can include:
- bruising easily
- small blood clots appearing under the nails
- bleeds in mucous membranes that line areas inside the body
- stool that is dark black, tar-like, or contains blood
When looking for signs of vitamin K deficiency in newborn babies and infants, doctors will also look for:
- bleeding from the area where the umbilical cord has been removed
- bleeding in the skin, nose, gastrointestinal tract, or other areas
- bleeding at the penis if the baby has been circumcised
- sudden brain bleeds, which are deemed severe and potentially life-threatening
To diagnose a vitamin K deficiency, a doctor will ask about a person’s medical history to see if they have any risk factors.
The doctor may use a coagulation test called the prothrombin time or PT test. They take a small blood sample and then add chemicals to observe how long it takes to clot.
Blood typically takes 11 to 13.5 seconds to clot. If it takes longer than this it may indicate a vitamin K deficiency.
People may need to avoid foods with high levels of vitamin K before taking this blood test.
If a person develops a vitamin K deficiency, a healthcare provider will give them a vitamin K supplement called phytonadione.
The person usually takes the supplement orally, though injections are also available if the person’s body is less able to absorb the supplement by mouth.
The dosage depends on the age and health of the individual. The usual dose of phytonadione for adults ranges from
A doctor will also consider whether a person is taking anticoagulants, as these can interact with vitamin K.
Vitamin K administered at birth, usually as a shot, can prevent a deficiency in newborn babies.
The American Academy of Pediatrics recommend that newborns receive a single shot of
A vitamin K shot is especially important for newborns under certain conditions. Risk factors for vitamin K deficiency bleeding include:
- premature delivery
- maternal use of antiseizure drugs, anticoagulants, or drugs for tuberculosis
- babies who have fat malabsorption due to gastrointestinal or liver disease
- newborns who do not receive an injection of vitamin K at birth
It is up to the parents to decide whether their baby receives a vitamin K injection. Experts recommend the injection as it can protect against problems such as intracranial hemorrhage, brain damage, and infant death.
Vitamin K deficiency in adults is very rare, as most people get sufficient vitamin K from their diet. If a deficiency does develop and remains untreated, it may result in excessive bleeding.
In infants, administering vitamin K at birth can prevent some problems from developing, including excessive bleeding.
A diet high in foods that contain vitamin K can help prevent vitamin K deficiency.