What Is Vitamin K and Why Does Your Baby Need It?

Vanessa Raymond Fact Checked
Baby in diaper stretching
© Diane Durongpisitkul / Stocksy United

Since 1961, the American Academy of Pediatrics has recommended that newborns receive a vitamin K injection within hours of birth. But recently, there’s been an increase in the number of parents who refuse vitamin K for their babies, and a corresponding increase in vitamin K deficiency bleeding.

Why does your baby need a shot of this vitamin that you may have never even heard of?

We took our questions about vitamin K to Elizabeth Flanigan, M.D., M.P.H., a UW Medicine specialist in neonatal-perinatal medicine who works in the Neonatal Intensive Care Unit (NICU) at University of Washington Medical Center and Valley Medical Center.

Q: What does vitamin K do?

A: Vitamin K is an essential vitamin that serves an important function in the formation of blood clots, and it also prevents abnormal bleeding. Low levels of vitamin K raise the risk of uncontrolled bleeding.

Q: Why is vitamin K important for my newborn baby?

A: Babies lack sufficient vitamin K at birth, which puts them at risk for vitamin K deficiency bleeding, a form of uncontrolled bleeding that can occur quickly and without warning in the brain or intestines. This form of uncontrolled bleeding can be life-threatening and may also lead to severe (irreversible) brain damage. 

A vitamin K injection after birth protects babies from this risk.

Q: Why don’t infants have enough vitamin K?

A: There is poor transfer of vitamin K across the placenta so even moms with good levels of vitamin K aren’t able to transfer it to their infants.

Also, human breast milk contains only very small amounts of vitamin K. That means that the babies of moms who breastfeed exclusively within the first 6 months of life do not receive enough vitamin K in their diet.

Babies begin to get vitamin K when they begin eating solid foods, typically around 6 months of age. 

Q: Is vitamin K a vaccine?

A: No, vitamin K is not a vaccine. Vitamins are essential nutrients that can’t be made by the body.

Vaccines work by triggering a baby’s immune system, but vitamin K doesn’t trigger the baby’s immune system. People confuse vitamin K with vaccines because it’s given by injection.

Q: Does the vitamin K shot have thimerosal in it?

A: No. (Thimerosal is a mercury-based preservative that has been used in the United States in medicines and vaccines.)

Q: Which infants are at greatest risk for vitamin K deficiency?

A: Infants of mothers who breastfeed exclusively are at the greatest risk for a deficiency because human breast milk does not contain sufficient quantities of vitamin K to prevent bleeding in infants.

Q: Is there a delayed or alternative schedule for administering vitamin K?

A: A delayed or alternative schedule for vitamin K does not work for babies. This is because a vitamin K injection given shortly after birth protects infants during the period of their highest risk: days to weeks after birth.

Some other countries use oral vitamin K but this form is not commercially available in the United States, and not approved by the FDA. Also the oral form of vitamin K does not protect the infant as well as the one dose given as an injection, and the bleeding can still occur.

Q: Why do some parents worry about giving their babies a vitamin K injection?

A: Parents have many reasons for declining treatments on the behalf of their newborns. Some cite not wanting to expose their infants to things that are seen as unnatural or harmful. Others confuse vitamin K with a vaccine and they have concerns about vaccines. Others are concerned about risk of side effects or complications.

One of the frequently-cited concerns is the possible risk of cancer. This concern originated from two studies (both published by same author) that suggested an association between the vitamin K injection and increased risk for some cancers in children in the United Kingdom.

This association has since been refuted. There have been many more studies—including one using the same data as the original articles—that did not show the same association or risk of cancer

In 2003, the American Academy of Pediatrics issued a policy statement reaffirming their recommendation that vitamin K be administered upon birth.

Q: When will my baby receive a shot of vitamin K?

A: Babies receive a shot of vitamin K within the first six hours after birth.

Q: Are there any side effects from a vitamin K injection?

A: Not really, although there can be pain during the injection itself and there can be a small amount of redness or bruising at the site of the injection.

Q: What do you recommend to parents?

A: I want new parents to understand what vitamin K is and why it is so important for their baby. Although these bleeds are rare, they are devastating to the families because they can be fatal or lead to severe, long-term neurologic consequences in those babies who survive. It is all the more tragic because these bleeds are preventable.

Vitamin K is a shot I recommend for all newborns. It’s that simple.