Vitamin K deficiency in adults is rare but does occur in infants. The main symptom of a vitamin K deficiency is excessive bleeding caused by an inability to form blood clots.

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.

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Vitamin K is found in some plant foods, such as leafy green vegetables, and is also produced by the body.

Vitamin K comes in two forms.

The first type is known as vitamin K-1 or phylloquinone and can be found in plants, such as spinach and kale.

The second is known as vitamin K-2 or menaquinone and is found in the body and created naturally in the intestinal tract.

Both vitamin K-1 and vitamin K-2 produce proteins that help the blood to clot. Blood clotting or coagulation prevents excessive bleeding internally and externally.

While vitamin K deficiency is rare, it means a 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.

However, 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 anticoagulants that 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

Other people who may be diagnosed with vitamin K deficiency have a condition that results in the body being unable to absorb fat properly. This is known as fat malabsorption.

People who have problems absorbing fat may have an associated condition, such as:

There are several reasons why newborn babies are more prone to vitamin K deficiency. These are:

  • drinking breast milk that is low in vitamin K
  • vitamin K does not transfer well from a mother’s placenta to her baby
  • a newborn baby’s liver is unable to use vitamin K efficiently
  • a newborn’s gut cannot produce vitamin K-2 in the first few days of life

Dieticians and nutrition experts recommend that adult males consume at least 120 micrograms (mcg) per day of vitamin K and women consume 90 mcg per day.

Foods that are high in vitamin K include green, leafy vegetables, prunes, and fermented dairy products.

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A person with vitamin K deficiency may bruise easily.

There are several symptoms associated with vitamin K deficiency, but the main one is excessive bleeding. Excessive bleeding may not be immediately evident, as it may only occur if a person is cut or wounded.

Additional signs of excessive bleeding can also 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. This test draws blood using a small needle. Chemicals are added to the blood, which is then observed to see how long it takes to clot.

If a person’s blood takes longer than 13.5 seconds to clot, the doctor may suspect a vitamin K deficiency.

Certain foods have high levels of vitamin K and should not be eaten before a test. These include some liver products, cauliflower, broccoli, chickpeas, kale, green tea, and soybeans.

If a person is diagnosed with vitamin K deficiency, they will be given a vitamin K supplement called phytonadione.

Phytonadione is usually taken orally, though it can also be given as an injection if a person has difficulty absorbing the oral supplement.

The dosage given depends on the age and health of the individual. The usual dose of phytonadione for adults ranges from 1 to 25 mcg.

A doctor will also consider whether a person is taking anticoagulants, as these can interact with vitamin K.

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Newborn babies may need a vitamin K supplement.

Vitamin K administered at birth can prevent a deficiency occurring in newborn babies. It is usually given as a shot.

The American Academy of Pediatrics recommend that newborns receive a single shot of 0.5 to 1 mcg of vitamin K-1 at birth.

A vitamin K shot is especially important for newborns under certain conditions. Risk factors for vitamin K deficiency bleeding include:

  • babies that are born prematurely
  • babies with mothers taking anti-seizure drugs, anticoagulants, or drugs for tuberculosis
  • babies who have fat malabsorption due to gastrointestinal or liver disease
  • newborns not given vitamin K at birth, breast-fed exclusively and exposed to antibiotics

It is up to the parents to decide whether or not their baby receives a vitamin K injection, although it is usually recommended.

Vitamin K deficiency in adults is very rare. However, if a deficiency is left untreated, it may result in excessive bleeding.

In infants, it is essential to administer vitamin K at birth to prevent poor outcomes from excessive bleeding, such as intracranial hemorrhage, brain damage, and infant death.