This story originally appeared as an article on the Bloomberg School of Public Health website and was summarized in The Uptake, a weekly newsletter offering expert insights from the Bloomberg School of Public Health.
When a baby is born, hospital staff move quickly through a standard checklist of newborn care: taking measurements, administering antibiotic eye ointment to prevent eye infections, and giving a small injection of vitamin K.
For many parents, it barely registers in the blur of those first hours—but that one shot in the thigh muscle may be one of the most consequential interventions in a newborn's life, dramatically reducing the risk of life-threatening bleeding.
"The vitamin K shot is one of the oldest, safest, and most effective preventive interventions in newborn medicine," says Mary Beth Howard, a pediatric emergency medicine physician at Johns Hopkins Hospital and core faculty in the Center for Injury Research and Policy. "It's very important that all babies receive it."
The American Academy of Pediatrics—which first endorsed the intervention in 1961—recommends the shot be administered within six hours of birth. But amid a flood of misinformation online, more parents are refusing the shot for their newborns, sometimes with devastating consequences—highlighting the need for better communication about its benefits and the risks of forgoing it.
"No parent wants their child to bleed to death," says Andrew Thorne-Lyman, a nutritional epidemiologist and associate professor in International Health. "No parent wants their child to have hemorrhaging in their brain."
Why newborns need vitamin K
Vitamin K is essential for blood clotting, but newborns are born with very low levels of the nutrient, making them vulnerable to vitamin K deficiency bleeding, or VKDB—a condition that can cause internal bleeding in the brain, intestines, and other vital organs.
The single vitamin K injection—typically 0.5 mg to 1.0 mg given just after birth— prevents VKDB during the critical first months of life while the baby is building up their own vitamin K stores and before they start eating solid foods around 4–6 months old.
Without the vitamin K shot, the risk of bleeding is up to 81 times higher, with incidents occurring in 1 in 14,000 to 25,000 babies.
While most adults naturally maintain healthy vitamin K levels produced by bacteria in the gut and a balanced diet, the nutrient "does not cross the placenta easily," Thorne-Lyman says, and once babies are born, breast milk does not provide sufficient amounts.
The risks of skipping the shot
The consequences of VKDB can be swift and devastating—and there's no reliable way to measure a baby's risk, says Howard. What makes the condition especially dangerous is that "oftentimes these infants look completely healthy beforehand," she says. "And the only sign that something is wrong is sudden, catastrophic bleeding, when the bleeding is already severe and difficult to reverse."
Brain bleeds are among the most serious outcomes. Depending on where blood accumulates and how quickly it is detected, consequences range from neurological impairment to death. "If [the hemorrhage] is pushing against the brainstem, which regulates a baby's breathing and heart rate, and it's not detected quickly enough, that has devastating consequences," Howard says.
After bleeding begins, treatment options are limited. Vitamin K can be administered as a last resort to help stop active bleeding, but damage already done to the brain may be permanent.
Howard and Thorne-Lyman—who has studied vitamin K deficiency in Bangladesh, where the vitamin K shot is not standard practice—have both witnessed cases of VKDB manifest as brain bleeds.
Howard says the rising number of parents refusing the intervention has added a new layer of complexity to diagnosing sick infants in the ED, where the most common cause of bleeding is trauma, such as a fall.
When evaluating infants who did not receive vitamin K injections, "clinicians may need to consider serious bleeding complications when evaluating otherwise nonspecific symptoms such as lethargy, vomiting, seizures, or pauses in breathing," says Howard.
Why some parents refuse vitamin K
Parents refuse the shot for a wide range of reasons. One 2019 qualitative study found the refusal was often driven by a broad aversion to anything perceived as foreign or interventional at birth.
Increasingly, refusals are driven by misinformation circulating on social media that often conflates the shot with vaccines simply because it is an injection administered at birth. "But it's not a vaccine—it's a vitamin supplement," Thorne-Lyman stresses. Oral vitamin K—sometimes offered if parents turn down the injection—is not a reliable alternative because absorption through a newborn's gut is inconsistent, and repeat dosing would be required throughout the newborn period, says Howard.
Other reasons parents object to the birth dose:
Fear of side effects: Parents have encountered unfounded claims online about dangerous complications. In reality, decades of use support the shot's safety profile.
The cancer myth: A small study from the 1980s suggested a possible link between the shot and childhood cancer, but subsequent larger, more rigorous studies have not confirmed that association. "We have strong evidence to support that it does not increase an individual's cancer risk," Howard says.
"Breast milk is enough": Some parents mistakenly believe breastfeeding provides sufficient vitamin K—but it does not, says Thorne-Lyman. Unlike vitamin D, which can be meaningfully enriched in breast milk if the mother is sufficiently supplemented, "even if the woman is eating a good diet that's rich in vitamin K sources, there is still a possibility that their child is going to be deficient," he explains. Formula-fed infants may have somewhat lower risk because formula contains added vitamin K, but the injection is still recommended for all newborns.
Delayed cord clamping: Some families believe that leaving the umbilical cord attached longer will transfer enough vitamin K from the placenta. "Placental transfer of vitamin K is very low, including through the cord blood, so delayed cord clamping does not provide sufficient vitamin K to prevent VKDB," Howard says.
A broader dynamic is also at play: Because VKDB became so rare after the shot was introduced, many parents have no frame of reference for how serious it can be, she says. "Because the underlying disease has become invisible, it produces a level of complacency."
What parents can do
Howard's advice is straightforward: Ask questions before delivery. Unlike vaccines given at 2- and 4-month well visits, the vitamin K shot is administered in the busy and often-overwhelming hours after birth, leaving little time for informed conversation.
"Parents, unfortunately, are turning to social media rather than being able to sit down with their pediatrician," she says, urging expectant parents to raise the topic with their OB or midwife in advance. She also encourages providers to raise the topic in prenatal visits to counter misinformation and emphasize the injection's benefits.
"We know now from decades of evidence and use that it is safe, effective, and necessary to prevent vitamin K deficiency bleeding, which can have deadly, or if not deadly, lifelong consequences for an infant."
