A vitamin supplement typically conjures up an image of pills you swallow or perhaps a chewable multivitamin, but that’s not the case for vitamin K administered to newborns. It does come in oral form, but it’s the vitamin K shot that’s most common and most effective—and most recently in the news.
Many people don’t even realize that newborns receive a vitamin K shot at birth even though it’s been recommended by the American Academy of Pediatrics since 1961. And for most of the time since then, no one really questioned the potentially life-saving intervention. But a small yet concerning uptick in parents refusing the shot has occurred in recent years, as I’ve written before in 2013 and in 2014.
Now a new study in the Journal of Medical Ethics explores the reasons that somewhere between 0.5% and 3% of parents decline the shot. The reasons range from faith-based ones to beliefs that it’s “unnatural” to anxiety about pain and possible side effects. The best antidote to fear, misinformation or a general lack of information is knowledge, so let’s review the basics of what vitamin K is, why it’s needed and what it does—and doesn’t—do. Much of this information is available is also covered in the book Emily Willingham and I wrote, The Informed Parent: An Evidence-Based Resource for Your Child’s First Four Years, and the study references are available here.
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What is vitamin K?
Vitamin K is a fat-soluble vitamin that’s actually named after what it does: Koagulation, the German word for coagulation. It activates the molecules (clotting factors) that allow our blood to clot. If our vitamin K levels drop too low, though the threshold varies from person to person, we can spontaneously bleed internally. We get about 90% of our vitamin K from diet (mostly leafy green vegetables) and about 10% from bacteria in our intestines.
Why would babies need vitamin K right after birth?
The vitamin is metabolized and stored in the liver—not free-floating throughout the body—so almost none of a pregnant woman’s vitamin K crosses the placenta. All babies are therefore born vitamin K-deficient, putting them at risk for uncontrolled bleeding, called vitamin K deficiency bleeding, if their vitamin K levels drop too low and they have not received a dose to hold them over until they’re eating solid foods (and their livers have developed sufficiently to extract and use the vitamin K in food). Though uncommon, vitamin K deficiency bleeding can have catastrophic consequences, potentially resulting in gross motor skill deficits; long-term neurological, cognitive or developmental problems; organ failure; or death.
How common is vitamin K deficiency bleeding?
The three types of vitamin K deficiency bleeding—early, classic and late—can occur in the brain or in the gut. Approximately 0.25% to 1.7% of newborns who don’t receive vitamin K at birth will experience classic or early vitamin K deficiency bleeding. Classic is within the first week after birth; early is in the first 24 hours. However, nearly all early vitamin K deficiency bleeding is secondary, which means the newborn has an underlying disorder or was born to a mother who was taking medications that inhibit vitamin K, such as anti-epileptic drugs, some antibiotics, tuberculosis drugs such as isoniazid or blood thinners such as coumarin or warfarin.
Late vitamin K deficiency bleeding, occurring when a baby is between 2 and 24 weeks old, affects an estimated 4 to 10 of every 100,000 babies who don’t receive vitamin K at birth. About one in five babies who develop late vitamin K deficiency bleeding die, and two of every five who survive have long-term brain damage. Because it’s rare and internal, it’s always easy for the bleeding to go undiagnosed for too long, which probably contributes to the high mortality and long-term effects. The treatment for the bleeding is vitamin K.
What did babies do before we gave the shot?
They died or suffered the other serious long-term consequences mentioned above. Babies have always been born deficient, but again, it’s easily missed or misdiagnosed, so the condition flew under the radar for most of human history. When first discovered in 1894, vitamin K deficiency bleeding was called hemorrhagic disease of the newborn. Even then, infants suffered so many other complications and diseases before vaccines and other medical advances were widely available that such a rare condition didn’t garner much attention or resources. As neonatal care improved, it became an unacceptable risk, and we learned in 1944 how to prevent it.
Why doesn’t breastfeeding or delayed cord clamping protect babies from vitamin K deficiency bleeding?
Cord blood is an excellent source of iron, and delayed cord clamping can offer benefits, but providing vitamin K isn’t one of them. Neither does breastmilk. Since the vitamin is stored in the liver and doesn’t cross the placenta or flow freely throughout the body, cord blood doesn’t offer any more vitamin K than what a baby arrives in the world with, and breastmilk passes along a measly 1 microgram per liter, no matter how many supplements a nursing mother might take.
In fact, exclusively breastfed babies have a higher risk than formula-fed babies of developing vitamin K deficiency bleeding because most formula is fortified with vitamin K (about 55 micrograms per liter). Nearly all babies who experience vitamin K deficiency bleeding today are exclusively breastfed.
Why do babies get an injection instead of taking it orally?
To almost entirely reduce the risk of vitamin K deficiency bleeding (nothing is 100%), the intramuscular shot is the way to go. It contains 0.5 to 1 mg of (depending on birth weight) vitamin K in one dose whereas oral vitamin K requires three carefully timed administrations—which are easy to forget, especially in the hectic first weeks after a newborn’s arrival. Oral vitamin K is also less effective than the shot—particularly for late vitamin K deficiency bleeding—because the shot’s vitamin K is absorbed more easily and lasts longer. Anywhere from 1 to 6 babies out of 100,000 who receive the oral vitamin K will still develop late bleeding.
What are the harms, risks or side effects of the vitamin K shot?
Vitamin K is one of the very few interventions with just about no risk of side effects except the temporary pain of an injection. Again, nothing is 100%, but the only documented effects are bruising at the injection site in some babies. After all, it’s an essential vitamin.
But there’s more than just vitamin K in there, right? What about the other ingredients?
Aside from the vitamin K, the preservative-free shots contain polysorbate 80, propylene glycol, sodium acetate anhydrous and glacial acetic acid—all safe, standard ingredients used to help the vitamin K dissolve, maintain the shot’s moisture or adjust the pH.
What about the research showing it can cause leukemia?
Concerns about the vitamin K shot and leukemia risk stem from a relatively small case-control study (fewer than 800 children) in 1992 which has never been replicated since. The year after it was published, two much larger studies (one with nearly 1.4 million children and another with more than 50,000 children) found no link between vitamin K and cancer or any other conditions. Neither another eight studies done later. There is no mechanism that could physiologically explain how an essential vitamin could cause leukemia, and none of the other ingredients in the shot have been linked to the blood cancer.
What’s the bottom line?
The vitamin K injection at birth is the safest, most effective intervention for preventing the rare but potentially fatal condition of vitamin K deficiency bleeding.
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