A new Swedish study on vitamin K has been getting a lot of attention. I’ve seen headlines and social media posts saying that babies who don’t receive the vitamin K injection are “50% more likely to bleed” or have “three times the risk of a brain bleed.”

Those statements certainly got people’s attention.

I wrote a social media post looking at problems with interpreting these figures from the abstract alone, which most people were doing at the time.

Now that I have read the full paper, I wanted to take a deeper dive into what the researchers actually found, what the numbers mean for individual babies, and some important limitations that are getting lost in the headlines.

I also highly recommend Dr Sara Wickham’s discussion of this paper in her newsletter (sign up for her newsletter if you haven’t already). Sara has literally written the book on vitamin K and informed decision-making, and her article: Sara Wickham: Vitamin K – evidence, risk and informed choice, raises several of the issues I discuss here.

Her website also has an excellent collection of vitamin K resources, and her book Sara Wickham: Vitamin K and the Newborn is a valuable resource for parents who want to explore this decision in much greater depth.

First, what did the study actually do?

The researchers looked at more than 2 million babies born in Sweden between 2003 and 2021, all born at 35 weeks or later.

Of the 2,020,302 babies included, 24,089 had no record of receiving intramuscular (IM) vitamin K at birth, meaning the vitamin K injection. The researchers then used Swedish health registers to look for recorded bleeding diagnoses during the first six months of life.

That wording matters.

I think it really important to note that the conclusion in the paper frames the issue in terms of increasing parental “refusal”, even though the researchers did not have information about why IM vitamin K was not recorded for individual babies. 

The study did not compare a clearly defined group of babies whose parents declined all vitamin K with a group who accepted it.

It compared babies with a record of intramuscular vitamin K with babies who had no record of intramuscular vitamin K.

More on this later.

A question about newborn vitamin K physiology

There is also a broader question worth keeping in mind.

Newborn babies naturally have lower levels of several vitamin-K-dependent clotting factors than adults. But their entire clotting system is also physiologically different, with a different balance of clotting and anti-clotting factors. This is known as developmental haemostasis (Favaloro & Lippi, 2017)

So it is reasonable to ask whether “lower than adult levels” should always be described as a deficiency or whether this is part of normal newborn physiology for most babies.

This is an important question, and one Dr Sara Wickham explores in much greater depth in her work on vitamin K and informed decision-making.

For parents wanting to explore this further, Sara’s website and her book Vitamin K and the Newborn are excellent resources. The book also includes a really useful decision-making tool to help parents work through the evidence, options, uncertainties and their own priorities.

But here is the really important issue: “bleeding” was not the same as VKDB

This is probably the most important limitation when trying to translate this study into meaningful information for parents.

The study was about vitamin K, but its primary outcome was not confirmed vitamin K deficiency bleeding (VKDB).

Instead, the researchers searched Swedish health registers for a broad range of standard diagnostic codes used in health records.

These included diagnoses related to vitamin K deficiency and haemorrhagic disease of the newborn, but also much broader categories of intracranial, gastrointestinal, respiratory, umbilical and soft-tissue bleeding.

The authors explicitly acknowledge this limitation.

They did not have the laboratory results or detailed clinical information needed to determine whether individual bleeding episodes met established diagnostic criteria for VKDB.

As they explain, their outcome captured:

“all atraumatic bleedings regardless of aetiology.”

They also acknowledge that this broader definition helps explain why the bleeding rates in their study are substantially higher than those reported in studies looking specifically at confirmed VKDB.

The phrase “atraumatic bleeding” can also be misleading.

It might sound as though these were spontaneous bleeds caused by an underlying clotting problem. But that is not what “atraumatic” establishes in this dataset.

It primarily describes how the bleeding was classified and coded.

This distinction is crucial.

We cannot take the figure of 1 in 157 and say:

“One in 157 babies who don’t have the vitamin K injection will develop VKDB.”

Nor can we say that 1 in 454 babies without documented IM vitamin K experienced a brain bleed caused by vitamin K deficiency.

That is not what this study measured.

It measured whether babies received one of a broad range of recorded bleeding diagnoses.

It cannot tell us how many of those diagnoses represented genuine vitamin K deficiency bleeding.

Why does it matter that these were not confirmed VKDB cases?

Because vitamin K does not prevent every type of bleeding.

Vitamin K is essential for normal blood clotting, and that can easily lead people to assume that giving vitamin K would prevent any bleeding episode.

But that is not how it works.

If a baby has a bleed primarily because of something else, for example, hypoxia, infection, a vascular abnormality or another coagulation disorder, giving vitamin K would not necessarily prevent that bleed.

That distinction is particularly important because some reporting of this paper gives the impression that the additional bleeding diagnoses in babies without documented IM vitamin K represent cases that would have been prevented by the injection.

But because the study did not establish the cause of those bleeds, it cannot tell us that.

Some of the gastrointestinal, soft-tissue, umbilical or intracranial bleeds captured in the study may indeed have been caused by vitamin K deficiency and therefore potentially preventable with vitamin K.

Others may have had completely different causes.

Without the babies’ clinical histories, clotting results and investigation findings, we simply don’t know which was which.

The study showed an association between documented IM vitamin K and fewer recorded bleeding diagnoses.

It did not establish that every additional bleed in the no-documented-IM group was caused by vitamin K deficiency or would have been prevented by vitamin K.

And that matters enormously when these findings are translated into information for parents.

The researchers argue that the relative differences between the groups are still useful when looking at the association between IM vitamin K and bleeding.

I can see the statistical argument they are making.

But that is not quite the same question a parent is trying to answer.

A parent considering vitamin K generally wants to know:

What is the chance that my baby will develop vitamin K deficiency bleeding if I choose this option versus that option?

This study cannot give us a precise answer to that question. It tells us that babies without documented IM vitamin K had more recorded bleeding diagnoses, but it does not tell us the absolute risk of confirmed VKDB or how many of those additional bleeds would actually have been prevented by vitamin K.

“No documented IM vitamin K” does not necessarily mean “no vitamin K”

You might notice I keep using the phrases “documented IM vitamin K”

This is another important distinction that gets lost very quickly once a study reaches the media.

The study determined whether a baby had received IM vitamin K from a checkbox in the birth record.

The authors acknowledge that this checkbox has never been formally validated, and that differences in electronic medical record systems may have resulted in babies being misclassified.

So the main comparison is not:

Vitamin K versus no vitamin K.

It is:

Documented intramuscular vitamin K versus no documented intramuscular vitamin K.

A word about the language of “education” and “refusal”

In their abstract, the authors concluded that their findings demonstrate a “need for continued education of parents and caregivers.”

And, in the Clinical and Research Implications section of the paper, they go further:

“Educational efforts to address parental refusal of intramuscular vitamin K should begin early…”

This seems like a big leap when they didn’t collect information on why babies potentially didn’t get IM vitamin K. They also admitted that it may have simply not been documented, but babies might actually have got it.

There are several possible reasons a baby might end up in the “no documented IM vitamin K” 

The study itself raises these possibilities:

Vitamin K may have been given by neonatal staff but not recorded in the maternal delivery chart. The authors specifically worried about this for babies admitted to a neonatal unit.

Documentation may have been poorer when a baby was unwell at birth. The researchers specifically mention babies with a low Apgar score as being at risk of “suboptimal documentation” of vitamin K.

Regional documentation problems. One region was excluded because more than 80% of babies had no recorded IM vitamin K, which the authors considered much more likely to reflect documentation error than true non-administration.

Under-reporting in non-hospital settings. The authors say the high proportion of home-born babies without documented IM vitamin K may partly reflect under-reporting outside hospitals.

The recording system itself may have misclassified babies. Vitamin K status was based on a checkbox in the delivery record, and that variable had not been validated.

Some babies received oral vitamin K rather than IM vitamin K. From 2012 onward, 1,457 babies in the group without recorded IM vitamin K had a recorded oral dose, so “no IM record” definitely did not always mean “no vitamin K”.

There was generally more missing information in the no-recorded-IM group. That included maternal and birth data, which adds to the concern that this group may have had more incomplete records overall.

Then there are some plausible possibilities that the paper does not specifically demonstrate, such as a rapid birth, transfer between care teams, or somebody simply forgetting to tick the box.

The researchers also did not have information on why IM vitamin K was not given.

Yet they suggested parental refusal is likely to explain many cases, but they did not actually have that information for individual babies.

That makes headlines about “parents refusing vitamin K” really inappropriate.

REFERENCES

Simatou E, Tsamantioti E, Hallström A, Stephansson O, Razaz N, Persson M, Bolk J. Vitamin K Prophylaxis in Newborns and Bleeding in Infancy. JAMA Pediatrics. Published online July 13, 2026. doi:10.1001/jamapediatrics.2026.2606.

Favaloro EJ, Lippi G. Translational aspects of developmental hemostasis: infants and children are not miniature adults and even adults may be different. Annals of Translational Medicine. 2017;5(10):212. doi:10.21037/atm.2017.04.18.