Vitamin K and childhood cancer

Medical misinformation from the CDC and more

Apr 03, 2025

Most parents who decline the vitamin K shot mere hours after the birth of their new baby do so out of a general skepticism for public health guidelines. Some mistakenly believe the shot is a vaccine. Few are well-educated on the genuine risks associated with the shot and fewer still are aware that it has been linked to childhood cancer.

Few, but presumably enough to prompt the CDC to include a reference to this supposedly debunked association on its FAQ page:

There are short and longer responses to this piece of misinformation. The short response is:

a) The “small study” was not small — it was a nationwide study of a snapshot in time (a week, to be precise) of births across the United Kingdom.

b) There were actually two studies — the one the CDC is referring to, and a follow-up study conducted by the authors of the first study, due to their concern at their findings.

c) If one includes the follow-up study among the “multiple larger studies” the CDC describes, then the results were mixed. Some studies (including but not confined to the follow-up) confirmed an association. Others had inconclusive findings.

d) Proving conclusively that one factor causes another is extremely difficult and rarely happens in modern medicine. However, the bar for safety is (or at least should be) set much higher when the drug concerned is something that “every newborn is expected to get.” Literally billions of people are affected, when one considers that vitamin K has been given as prophylaxis for over 60 years.

And now for the longer response.

The expected and unexpected risk factors for cancer

The background to this story comes in the form of a study published in 1989 by the Oxford Survey of Childhood Cancers, which revealed associations between childhood cancer and a number of factors: the mother undergoing an X-ray during pregnancy; use of pethidine (Demerol) during labor; vaccines; and other drugs used by the mother including fever-reducers and pain-relievers.

This was a retrospective study of 8,059 children who died of cancer, compared with a number of controls. Some of the findings raised eyebrows in the scientific community and a number of researchers decided to make an investigation of their own.

The result was an article published a year later in the British Journal of Cancer titled, “Factors associated with childhood cancer in a national cohort study.”

Since the original retrospective study had certain drawbacks (primarily, imperfect recall of information such as when hospital staff or parents are asked which drugs they used), these researchers conducted a new study based on data from mothers and babies who had been followed from birth, in an attempt to confirm or refute the Oxford findings.

The data had been collected from 1970 onward, on 16,193 babies born in a single week in April of that year. The children had been followed up during the first seven days of life and then at ages five and ten. 33 of the children had developed cancer by age ten which translated to a rate of 2.04 per 1,000 births.

For the purposes of the study, the records of each child who developed cancer were matched with three controls, using computerised matching to assign controls with similar backgrounds, such as the age of the mother at the birth. As they had expected, the authors of the study confirmed associations between maternal X-rays, smoking during pregnancy, and use of analgesic drugs (such as pethidine) during labor with later cancer diagnoses of the children. These associations were all statistically significant.

However, the study’s authors also made some unexpected findings:

Unexpected statistically significant associations were found with delivery of the child outside term, and drug administration in the first week of life. The latter was found in the absence of an association with neonatal abnormalities in the child and relates mostly to the administration of prophylactic drugs such as vitamin K.

Being born before 39 weeks of pregnancy or after the 41^st week appeared to be linked with a subsequent cancer diagnosis; this was the first unexpected finding. The other surprising finding was related to drugs given to the baby in the first week of life. In most cases, the drug concerned was vitamin K (which, during the period concerned in the UK, was given intramuscularly, in accordance with official policy).

Intramuscular Vitamin K doubles the risk

In most of the cases of childhood cancer (31 out of 33), at least two risk factors were present in the child. Analysis of the data also revealed a highly significant proportional relationship between risk factors and diagnosis, i.e., the more risk factors present, the greater the likelihood of being diagnosed with cancer (P<0.0001).

The researchers then conducted a logistic regression analysis in order to discover which of the risk factors were independently associated with cancer and which only increased the likelihood of the diagnosis but did not appear to prompt it. The results of the logistic regression analysis were:

Maternal smoking was independently associated with cancer diagnosis (OR 2.5).
Administration of drugs (primarily vitamin K) to the baby in the first year of life was independently associated with cancer diagnosis (OR 2.6).
Pethidine (Demerol) in labor was independently associated with cancer diagnosis (OR 1.7).
Other factors such as maternal X-rays appeared surprisingly not to be independently associated with cancer development.

Plus a possible link to colostrum deprivation

The researchers added that only 9 out of the 33 babies (28 percent) who later developed cancer were ever breastfed by their mothers, as opposed to 46 of the 99 controls (46 percent). They wrote that this was “a difference that was suggestive but not statistically significant.” Nonetheless, in light of what we have discussed in part one of this article, relating to the importance of colostrum for vitamin K, this difference may be more significant than the researchers realized. Furthermore, babies fed formula are exposed to high levels of vitamin K in their “milk,” adding to their total exposure.

In any case, the finding that most alarmed them, given the widespread administration of vitamin K to babies, was one they had not expected to find and had not even been looking out for:

“The association with vitamin K was unexpected and fitted no prior hypothesis.”

Vitamin K administration appeared to increase the likelihood a child would develop cancer before the age of 10 by a factor of 2.6.

The researchers thus concluded that,

It is important that this association with a certainly useful drug be tested in another series of cases.

And who followed up? Not mainstream science…

Did the scientific community share their concern and leap to conduct additional studies? Not precisely. In fact, not at all. In the end, it was the same group of researchers who unearthed more data in order to test their findings. The CDC makes no mention of the existence of this follow-up study. No more does the American Academy of Pediatrics. Only “by chance,” while looking at a study published in the New England Journal of Medicine in 1993 did we discover this second study referenced in a footnote.

The follow-up study was published in the British Medical Journal (BMJ) in 1992. This is no fringe publication; it is one of the most respected medical journals in the world. The title of the study is: “Childhood cancer, intramuscular vitamin K, and pethidine given during labour.”

Objective: To assess unexpected associations between childhood cancer and pethidine given in labour and the neonatal administration of vitamin K that had emerged in a study performed in the 1970 national birth cohort.
Design and setting: 195 children with cancer diagnosed in 1971-March 1991 and born in the two major Bristol maternity hospitals in 1965-87 were compared with 558 controls identified from the delivery books for the use of pethidine during labour and administration of vitamin K.

The results of their analysis confirmed a significant association between vitamin K administration and cancer (with the risk almost doubled). With regard to use of Demerol during labor, however, no significant association was confirmed.

Results: Children of mothers given pethidine in labour were not at increased risk of cancer (odds ratio 1.05) ... but there was a significant association (p=0.002) with intramuscular vitamin K (odds ratio 1.97, 95% confidence interval 1.3 to 3.0) when compared with oral vitamin K or no vitamin K.

The researchers also examined oral vitamin K supplementation and found that it did not appear to increase the risk of a later cancer diagnosis:

There was no significantly increased risk for children who had been given oral vitamin K when compared with no vitamin K (odds ratio 1.15, 95% confidence interval 0.5 to 2.7).

To rule out the effect of various other factors, the researchers repeated their analysis taking into account the type of delivery and admission to the NICU, but this did not affect the results. They also excluded all cancers detected in the first year of life, in case they were already present before administration of vitamin K and could not be linked — but the significant association between vitamin K and cancer remained. The researchers then checked the data for associations between other known risk factors and cancer, to ensure that the data being used were typical, and found that all other results were as expected, and thus,

... there was little to suggest that the effect of intramuscular vitamin K was an artefact consequent on other variables.

Notably, the link between leukemia and vitamin K was stronger than a generalized risk of cancer — the likelihood of developing this form of cancer following intramuscular (IM) vitamin K at birth was multiplied by 2.65 (with a 95% confidence interval of 1.32 to 5.24).

A cost-benefit analysis

The authors of the study were not unaware of the potential risks of withholding vitamin K from newborns. In order to compare the risks with those they discovered in their analyses, they used data from a nationwide study conducted in the UK between 1987 and 1990 (the study we cited in part two of this series), while noting that similar rates of infant hemorrhaging had been found in Germany:

A recent British study identified cases in the British Isles during 1987-90. The authors showed that the risk varied from 4.4 per 100,000 in those given no vitamin K prophylaxis to 1.4 per 100,000 in those given oral vitamin K and 0.11 per 100,000 in those given intramuscular vitamin K. A similar study in Germany produced similar results (7.2, 1.4, 0.25 respectively).
These figures provide the means to calculate the possible benefits in a population with 700,000 births annually [among which around 980 cases of cancer would ordinarily be detected].

The researchers then calculated that in the event vitamin K IM supplementation doubled the risk of developing cancer:

If no baby received any vitamin K then there would be about 30-60 cases of late hemorrhagic disease and no extra cancers.
If all babies received oral vitamin K there would be about 10 cases of late hemorrhagic disease and no extra cancers.
If all babies received intramuscular vitamin K there would be one case of late hemorrhagic disease and 980 extra cancers.

Around 3.6 million babies are born each year in the United States. So let’s consider the hypothetical case where they are all getting the IM vitamin K shot. Around 5,040 children will develop cancer who would not have otherwise.

And the authors of the study conclude, as most of us likely would as well:

The prophylactic benefits against haemorrhagic disease are unlikely to exceed the potential adverse effects from intramuscular vitamin K. Since oral vitamin K has major benefits but no obvious adverse effects this could be the prophylaxis of choice.

When is a deficiency not a deficiency?

Although their findings appeared to strongly favor oral supplementation with vitamin K for all newborns, the researchers remained troubled by the basic premise of modern medicine with relation to vitamin K. How is it logical, they argued, that after so many years of evolutionary change, all human beings are still born deficient in a vital substance and need supplementation? One does not have to believe in evolution in order to share this skepticism — it is even more inconceivable that God would have created man in need of an injection mere hours after birth.

It has always seemed physiologically perverse that evolution should have permitted the development of what is termed vitamin K deficiency in normal term infants who are breast fed, resulting in a small but definable risk of haemorrhagic disease of the newborn. The most likely explanation for this situation is that there is some evolutionary advantage that outweighs this risk.
The finding of an increased incidence of childhood cancer in children given intramuscular vitamin K in the neonatal period suggests that a relative deficiency in vitamin K during this critical phase of rapid growth and development may protect vulnerable tissues from mutagenesis. The protection afforded by oral vitamin K against haemorrhagic disease does not appear to carry the same risk of inducing malignancy, so it may be prudent to use oral rather than intramuscular vitamin K.

Thus they surmised that there is likely some evolutionary advantage inherent in the low levels of vitamin K seen in newborns. Perhaps low levels of vitamin K are actually desirable in important ways. Well, not “perhaps,” it turns out. This had already been demonstrated in animals:

Rather than vitamin K being harmful, the deficiency state might be protective. Experiments with rodents have indicated a significant reduction in tumour growth in animals made artificially deficient in vitamin K.

When is science not scientific?

The findings on cancer reductions in rodents due to vitamin K deficiency were published in 1977. Why did no one wonder whether the same might apply to humans? In fact, some people did wonder and they also investigated. In the 1980s, Drs. LG and ED Israels at the University of Manitoba started researching vitamin K and rodent cancer — and then human cancer. They published a series of studies on their research in the 1990s, by which time they had contacted the authors of the two British studies, to explain the plausibility of their findings. Other concerned researchers also contacted them.

The authors of the UK study wrote:

... the vitamin K results were unexpected, although we have since become aware that the hypothesis had already been raised in Canada (LG Israels, personal communication) and Germany (AH Sutor, personal communication).

And yet, despite the fact that vitamin K was by then being given to millions of babies each year, it seems that no one beyond a handful of scientists had seen fit to wonder whether injecting so much of this substance into a tiny newborn was truly safe:

This study provides an example of the unexpected generation of a hypothesis as the result of a data trawl followed by the testing of that hypothesis on a different data set. These appear to be the only two studies that have ever looked at intramuscular vitamin K in relation to cancer. The fact that both, although methodologically different, have shown similar results strengthens each of these results.

In the fourth and final part of this series, we will discuss the response of the scientific community to this association between intramuscular vitamin K and childhood cancer, as well as the true rates of hemorrhage in young babies.

Disclaimer: The information contained in this article is for educational and information purposes only and is not intended as health, medical, financial, or legal advice. Always consult a physician, lawyer, or other qualified professional regarding any questions you may have about a medical condition, health objectives, or legal or financial issues.