Vitamin K 101: The Newborn Shot, Explained

‍What Is Vitamin K?

In addition to helping with bone development, Vitamin K is a critical nutrient your body needs to make blood clot. Clotting is how your body stops bleeding after a cut or injury. Without enough vitamin K, even a small injury can bleed for a long time and be hard to stop.

Most people get plenty of vitamin K from food, like leafy green vegetables, and from bacteria that live in the gut and make it naturally. But newborn babies are different. They are born with very little vitamin K already in their bodies, and it takes time for their bodies to start making more on their own.

Why Newborns Are at Risk

Two things leave newborns short on vitamin K:

• Very little vitamin K crosses from a mother to her baby before birth.
• A newborn's gut has not yet grown the bacteria that make vitamin K, so the baby cannot make much of their own yet.

This puts newborns at risk for a rare but serious bleeding disorder called vitamin K deficiency bleeding, or VKDB. VKDB can cause bleeding inside the body, including in the brain, and can be deadly. It is rare, which is part of why many parents and even some doctors have never seen a case — but doctors still take it seriously because of how severe it can be when it happens.

What the Shot Does

The American Academy of Pediatrics recommends that every newborn get one shot of vitamin K, usually given into the thigh muscle during the hospital stay right after birth. The shot quickly brings the baby's vitamin K up to a safe level while their body learns to make its own.

Some countries give vitamin K as drops by mouth instead of a shot. The shot works better. An oral dose does not get absorbed as well, and it has to be given more than once over several weeks to work — so a baby could miss a dose. The shot is a single, reliable dose that protects the baby from birth.

Why This Still Matters Today

Most parents choose the shot for their baby, and it works. Since the American Academy of Pediatrics first recommended it in 1961, the shot has cut cases of serious, late-onset bleeding by about 98%.

But two recent studies in JAMA and JAMA Pediatrics, covering more than 11 million US newborns from 2017 to 2025, found that a small but growing share of parents are skipping the shot - nonreceipt roughly doubled over that time, and today around 1 in 20 newborns misses it.

As more parents skipped the shot, bleeding problems in babies became more common. Among the same 11 million newborns, diagnosed vitamin K deficiency rose more than threefold, and VKDB rose more than fourfold, between 2017 and 2025. Looking at the babies who actually got diagnosed with VKDB, 4 out of 5 had not received the shot - strong evidence that the shot is what was protecting them.

One other JAMA study found that babies who skipped the shot were more likely to have any bleeding problem in their first six months, and more than twice as likely to have bleeding in the brain or to die from a bleeding problem during their hospital stay after birth. Researchers estimate that for roughly every 114 babies who go without the shot, one baby ends up with a bleeding problem the shot could have helped prevent.

VKDB is still rare overall, and the exact reasons more families are skipping the shot are not fully known. But the data are a reminder that this one quick shot continues to do an important job: protecting newborns during the weeks before their own bodies can make enough vitamin K on their own.

Sources: JAMA, November 2026 and JAMA Pediatrics, November 2026

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