Part 3 - Vitamin K for newborns: Injection vs oral, & K1 vs K2

By Dr. Sarah Slater, DNP, CPNP-PC, ECS Specialist

There is a lot of fear and confusion surrounding the “best” way to give vitamin K to newborns, especially when families are choosing between injection and oral dosing.

In the United States, the standard recommendation is the vitamin K injection. It is quick, it is given once, and it virtually eliminates the risk of missed doses or absorption problems. This recommendation does not mean that oral vitamin K is unsafe or ineffective. Instead, it reflects how our healthcare system functions. At a population level, the system prioritizes the option with the lowest chance of error across millions of families.

That distinction matters, because science tells us something important. Oral vitamin K does work. It is safe. And it has been well studied. The key factor is not whether oral vitamin K works, but how it is given.

Large European studies show that oral vitamin K can be highly effective when it is given correctly, consistently, and for a long enough period of time. This is especially true for healthy, full-term infants with normal liver function and normal fat absorption. One of the most helpful examples comes from Denmark.

Denmark studied an extended oral vitamin K1 regimen in which babies received weekly doses over the first few months of life, rather than a single dose or a short series. In a national cohort of nearly 400,000 infants, this weekly oral regimen resulted in zero cases of vitamin K deficiency bleeding. Protection was comparable to the vitamin K injection, as long as families followed the protocol consistently. Breastfeeding rates in Denmark are high, so these outcomes were not simply explained by formula feeding, which still does not provide adequate vitamin K. The success of this approach depended on ongoing dosing and strong parental adherence, which was reported to be very good.

This contrasts with shorter oral regimens, such as the commonly cited three-dose protocol given at birth, around one week, and again at four to six weeks. Studies from Germany, Switzerland, and the Netherlands show that while this three-dose approach significantly reduces early and classic vitamin K deficiency bleeding, it does not fully protect against late vitamin K deficiency bleeding, even when families follow it correctly. Because of this, several countries moved away from short oral regimens and adopted extended weekly or daily dosing schedules that more closely mimic the steady vitamin K exposure seen in formula-fed infants.

Taken together, this research shows that oral vitamin K can work very well, but only when everything goes right. It requires the correct form of vitamin K, the correct dose, the correct formulation, and consistent dosing over time. If doses are missed, spit up, poorly absorbed, or stopped too early, the risk of bleeding increases. If a baby has an unrecognized absorption issue, the risk also increases. This is why the injection remains the default recommendation in the United States. Not because oral vitamin K is inferior, but because the injection removes variables that can interfere with absorption and reliability.

A major source of confusion comes from misunderstanding the two different forms of vitamin K, which are often grouped together even though they serve very different roles in the body. These forms are K1 and K2.

Vitamin K1, also called phylloquinone, is the form that prevents bleeding. It comes from the diet, especially green leafy vegetables, and it is not made by the body. Breast milk does not contain enough vitamin K1 to protect newborns. Vitamin K1 is fat soluble, meaning it must be given with something fatty, such as breast milk or formula, to be properly absorbed. Babies are born with very low vitamin K1 stores and typically do not reach protective levels until around twelve weeks of age.

Vitamin K1’s job is to activate clotting factors, especially a protein called prothrombin. Prothrombin helps make blood clot. A helpful way to think about this is that prothrombin is the car, and vitamin K1 is the fuel. Without fuel, the car cannot run. Without vitamin K1, prothrombin exists, but it does not function. This is why vitamin K1 must be supplemented to protect a newborn from bleeding.

This also explains another common myth. Some parents assume they can replace vitamin K1 with products such as vitamin D plus K2 drops. Unfortunately, this does not work. Vitamin K2 does not prevent newborn bleeding and does not protect against vitamin K deficiency bleeding. This misunderstanding alone accounts for a significant number of preventable cases.

Vitamin K2, also called menaquinone, serves a different role in the body. Its primary function is helping move calcium into bones and teeth and keeping calcium out of blood vessels. Although vitamin K2 is produced by gut bacteria, newborns are not born with those bacteria. Even so, vitamin K2 plays no role in preventing newborn bleeding.

This information can feel complex, but the takeaway is simple. Oral vitamin K1 can be highly effective when used correctly and consistently in ideal circumstances, as shown by Denmark’s weekly dosing data. However, the vitamin K injection remains the most reliable and forgiving option when the goal is to protect every baby, including those with hidden absorption risks.

This conversation is not about right versus wrong. It is about understanding the science, the trade-offs, and the level of reliability families are comfortable with when making an informed decision. Many parents are capable of following oral regimens well. The problem is that they are not always given the information, support, or trust needed to make that choice confidently.

What I love most about practicing Direct Primary Care with Balanced Kids is the close, real relationship I get to have with families.

I want families to know that I am not constrained by insurance rules or health system pressures. I am not forced into rushed visits or volume-based care. That gives me the time and space to walk through these decisions in detail and support truly individualized choices.

If you have a full-term, healthy newborn and choose oral vitamin K1, I will support you. I will teach you exactly how to give it, how often to give it, and what matters most to keep your baby protected.

If you forget a dose, don't panic! I am a text away, and we will talk through the next steps together.

If you later realize that remembering weekly dosing is not working for your family, that is okay too. I can come to you and administer preservative-free vitamin K by injection at any time. All that matters to me, is that your baby is protected.

It does not need to be complicated or stressful. What's important is that your baby receives vitamin K1, and my role is to make that as easy, flexible, and supported as possible for your family.

Here is a link to explore the Denmark Study at your leisure CLICK HERE.

Stay tuned for the final part of our Balanced Kids Vitamin K Series - Part 4: Safety, Mistrust, and Informed Choice — Bringing the Vitamin K Conversation Full Circle.