The Vitamin K Shot: What It Is For, How Well It Works, and Why Fewer Babies Are Getting It

A plain-language guide to a 2026 review of newborn vitamin K prophylaxis — the biology, the evidence, the alternatives, and the questions families most often ask

Newborn babies are born with very little vitamin K, the nutrient the body needs to make blood clot, and for six decades a single injection given shortly after birth has protected them from rare but devastating bleeding. A 2026 review gathers what is known about why babies are so vulnerable, how well the injection and its oral alternatives actually work, and why a growing number of families are choosing to decline it.

Why a healthy baby needs something added at birth

Almost everything a newborn needs is already built in. Vitamin K is the striking exception, and the reason is not diet or bad luck — it is the ordinary sequence of how a baby is made. Vitamin K is the ingredient the liver uses to switch on several of the proteins that make blood clot. Without enough of it, those proteins are still produced, but in an inactive form, so a baby can bleed even though nothing is wrong with the blood itself.

A newborn is short of vitamin K at four points at once, and a 2026 review by paediatricians and neonatal specialists at the University of Catania in Sicily, Italy, sets these out clearly [1]. Very little vitamin K crosses the placenta during pregnancy — levels in cord blood are dozens of times lower than in the mother. The baby's liver, which stores vitamin K, is not yet efficient at taking it up. The long-lasting forms of vitamin K that make up around 90% of an adult's liver stores are essentially absent at birth. And the gut bacteria that produce vitamin K in older children and adults have not yet arrived; a newborn's intestine is close to sterile in the first days of life [2].

Breast milk, which is the best food for a baby in almost every other respect, contains very little vitamin K — far less than infant formula, which is fortified with it [1]. This is worth stating plainly because it is so often misunderstood: exclusively breastfed babies are at higher risk of vitamin K deficiency bleeding, not lower. That is not a reason to avoid breastfeeding. It is the reason the vitamin K dose exists.

What can happen without it

Doctors group vitamin K deficiency bleeding, or VKDB, into three types by when it appears. Early bleeding, in the first 24 hours, is usually linked to medicines the mother took during pregnancy. Classic bleeding, between days two and seven, tends to show up as oozing from the skin, the umbilical stump, or the gut, and is rarely life-threatening. Late bleeding, from two weeks up to six months in exclusively breastfed babies, is the form everyone is trying to prevent: it often appears first inside the skull, with little warning [1].

The numbers give a sense of the scale. Without any prevention, late bleeding affects somewhere between 10 and 80 babies in every 100,000. In countries where all babies receive vitamin K, that falls below 3 in 100,000. Among babies who survive bleeding into the brain, 40% to 55% are left with lasting neurological problems. Looked at another way: before prevention became routine, roughly 1,700 babies per 100,000 had some form of this bleeding; afterwards, around 1 per 100,000 [1]. It is genuinely rare, and it is genuinely serious. Both halves of that sentence are true, and families deserve to hear both.

How the injection became standard — and then became controversial

The American Academy of Pediatrics first recommended giving vitamin K by injection to all newborns in 1961, and it still recommends a single 1 mg intramuscular dose for babies over 1500 g, with a smaller weight-based dose for the smallest preterm babies [3]. For thirty years this was uncontroversial.

Then, in 1992, a study from Bristol in England reported a possible link between the vitamin K injection — but not oral vitamin K — and childhood cancer, and suggested that giving it by mouth might be the safer course [4]. The finding travelled far and fast. It also turned out to be wrong: no later study reproduced it, and a recent analysis of early-life nutrition and childhood leukaemia found no association at all [1]. But by then several European countries had moved to oral schedules, and the claim itself never fully disappeared from the internet. Much of today's hesitancy traces back to a single unreplicated study from more than thirty years ago.

That history is why guidelines differ from country to country. European paediatric guidance now accepts three options: a single 1 mg injection at birth; three 2 mg oral doses at birth, at four to six days, and at four to six weeks; or 2 mg by mouth at birth followed by 1 mg weekly for three months. The oral route is not considered suitable for premature or unwell babies, or for those with liver or gut conditions that stop them absorbing it [5].

How well does it actually work?

Very well — with an important caveat about what kind of evidence exists.

Compared with no prevention at all, the injection reduces vitamin K deficiency bleeding by roughly 97% to 98%. In data gathered from national monitoring programmes across four countries, babies who got the injection had about one-fiftieth the risk of late bleeding compared with babies who got nothing. Compared with the injection, a single oral dose left babies at roughly 24 times the risk. Multiple oral doses came much closer to the injection, and the difference was small enough that it could have been chance [6].

The caveat is that most of this comes from tracking large populations over time rather than from randomised trials, in which babies would be assigned to one approach or another by chance. For late bleeding — the most serious form — no such trial has ever been done. That is not evasion; it is simply the honest state of the evidence, and it reflects an ethical reality: once an inexpensive treatment appears to prevent brain bleeds in newborns, it becomes very difficult to justify withholding it from half of a study group in order to prove the point more formally.

Fewer babies are getting it, and it is showing up in the data

Two large recent studies have measured what happens when coverage slips. In the United States, a study of more than five million newborns found that the share not receiving the injection rose from 2.92% in 2017 to 5.18% in 2024. The increase was concentrated in vaginal births and in birth settings that use fewer medical interventions, and it started before the pandemic [7].

In Sweden, researchers followed 2,020,302 babies born between 2003 and 2021 and identified 24,089 with no record of having received the injection. The share without it fell in the early years, to 0.66% in 2006, then more than doubled to 1.50% by 2021. Babies who did not receive it were about one and a half times as likely to have a bleeding episode in their first six months, and about three times as likely to have bleeding inside the skull [8].

Where a baby is born matters a great deal. Declining the injection is uncommon in hospitals — between 0% and 3.2% in the United States — but reaches around 14.5% at home births and 31% in freestanding birth centres [9]. And the reasons differ around the world. A survey of 685 doctors across 38 countries found that in wealthier countries the main obstacle is families declining the injection, while in lower-income countries it is that the vitamin is simply not available [10].

The reasons families give are worth taking seriously rather than dismissing. Most concerns are about the injection itself — the pain, the idea of a needle in the first hour, questions about the other ingredients in the vial — rather than about vitamin K [1]. Many parents are drawn to keeping birth as free of intervention as possible. A smaller group has encountered the disproven cancer claim. If the pain is the concern, it is worth knowing that holding the baby skin-to-skin, breastfeeding, or giving a little sugar solution during the injection measurably reduces distress, and any unit can offer this.

What families and researchers are still working out

A few genuinely open questions remain, and they are mostly about what happens after the first dose. One study of healthy, exclusively breastfed, full-term babies found that a daily oral top-up from discharge until 14 weeks lowered a blood marker of vitamin K shortage more effectively than the single injection at birth had [11]. Another found that exclusively breastmilk-fed premature babies developed signs of vitamin K shortage in early infancy even after receiving the injection at birth — something the researchers thought could be prevented with routine drops after going home [12]. Neither study measured actual bleeding, so these are early signals rather than a change in advice.

Researchers are also still comparing oral schedules to work out which one protects best when families follow it as intended [13][14], and there is a real gap in knowledge about the right dose for the smallest premature babies, where the entire randomised evidence base amounts to a single study of 80 infants [15].

What this means for you and your baby

If your baby has had the injection, the protection is excellent and no further action is needed. If you would prefer the oral route, it can work — but only if every dose is given, including the ones due weeks after you are home, and it is not suitable if your baby was born early, is unwell, or has a liver or gut problem. Ask for the dates in writing before you leave hospital.

The most useful thing this review says to families is about timing: most parents who decline have already decided before labour begins, so the delivery room is the worst possible place to have this conversation for the first time. If you have questions — about pain, about ingredients, about anything you have read online — the right moment to raise them is at an antenatal visit, when there is time to answer them properly and no one is in a hurry. That is a conversation your midwife or paediatrician will welcome, and it is one you are entitled to have in full.

References

  1. Mirone A, Mannino D, Leonardi R, et al. Vitamin K Prophylaxis in Newborns: A Narrative Review of the Molecular Basis, Clinical Evidence, and Comparative Effectiveness of Intramuscular Versus Oral Administration and Parental Hesitation. Int J Mol Sci. 2026;27(4):1669. doi:10.3390/ijms27041669 ↩
  2. Shearer MJ, Fu X, Booth SL. Vitamin K nutrition, metabolism, and requirements: current concepts and future research. Adv Nutr. 2012;3(2):182–195. doi:10.3945/an.111.001800 ↩
  3. Hand I, Noble L, Abrams SA. Vitamin K and the Newborn Infant. Pediatrics. 2022;149(3):e2021056036. doi:10.1542/peds.2021-056036 ↩
  4. Golding J, Greenwood R, Birmingham K, Mott M. Childhood cancer, intramuscular vitamin K, and pethidine given during labour. BMJ. 1992;305(6849):341–346. doi:10.1136/bmj.305.6849.341 ↩
  5. Mihatsch WA, Braegger C, Bronsky J, et al. Prevention of Vitamin K Deficiency Bleeding in Newborn Infants: A Position Paper by the ESPGHAN Committee on Nutrition. J Pediatr Gastroenterol Nutr. 2016;63(1):123–129. doi:10.1097/MPG.0000000000001232 ↩
  6. Sankar MJ, Chandrasekaran A, Kumar P, Thukral A, Agarwal R, Paul VK. Vitamin K prophylaxis for prevention of vitamin K deficiency bleeding: a systematic review. J Perinatol. 2016;36(Suppl 1):S29–S35. doi:10.1038/jp.2016.30 ↩
  7. Scott K, Miller E, Culhane JF, et al. Trends in Vitamin K Administration Among Infants. JAMA. 2025;335(3):272–274. doi:10.1001/jama.2025.21460 ↩
  8. Simatou E, Tsamantioti E, Hallström A, et al. Vitamin K Prophylaxis in Newborns and Bleeding in Infancy. JAMA Pediatr. Published online July 13, 2026. doi:10.1001/jamapediatrics.2026.2606 ↩
  9. Loyal J, Shapiro ED. Refusal of Intramuscular Vitamin K by Parents of Newborns: A Review. Hosp Pediatr. 2020;10(3):286–294. doi:10.1542/hpeds.2019-0228 ↩
  10. Sirachainan N, et al. International Perspectives on Vitamin K Deficiency Bleeding in Infants: A Cross-Sectional Questionnaire-Based Survey. Pediatr Blood Cancer. Published online July 8, 2025:e31889. doi:10.1002/pbc.31889 ↩
  11. Perrone S, De Bernardo G, Lembo C, et al. Vitamin K insufficiency and the prophylaxis strategy in term healthy infants: a multicentre study. Eur J Clin Invest. 2024;54:e14141. doi:10.1111/eci.14141 ↩
  12. Clarke P, Shearer MJ, Card DJ, et al. Exclusively breastmilk-fed preterm infants are at high risk of developing subclinical vitamin K deficiency despite intramuscular prophylaxis at birth. J Thromb Haemost. 2022;20(12):2773–2785. doi:10.1111/jth.15874 ↩
  13. Jullien S. Vitamin K prophylaxis in newborns. BMC Pediatr. 2021;21(Suppl 1):350. doi:10.1186/s12887-021-02701-4 ↩
  14. Takahashi D, Egami N, Ochiai M, et al. Vitamin K prophylaxis in neonates: comparing two different oral regimens. J Perinatol. 2024;44:1491–1495. doi:10.1038/s41372-024-01981-9 ↩
  15. Ardell S, Offringa M, Ovelman C, Soll R. Prophylactic vitamin K for the prevention of vitamin K deficiency bleeding in preterm neonates. Cochrane Database Syst Rev. 2018;2(2):CD008342. doi:10.1002/14651858.CD008342.pub2 ↩