Vitamin K and Vitamin K Deficiency Bleeding
Vitamin K lets your blood clot. Adults rarely run short, but every baby is born low on it. One dose at birth prevents a rare, sometimes fatal bleed, which is why it’s offered to every newborn in Australia.
Why newborns are low
- Very little vitamin K crosses the placenta.
- A newborn’s gut doesn’t yet have the bacteria that make it.
- Breast milk has only small amounts (about 1–2 micrograms per litre, versus at least 30 in formula). That’s normal, and breast milk is still best, but it’s why breastfed babies rely on the birth dose.
- A newborn liver makes clotting factors at only about a third to half of adult levels.
The three kinds of bleeding
- Early (first 24 hours): mostly in babies whose mothers took certain medicines in pregnancy, such as some seizure medicines, rifampicin or warfarin.
- Classic (first week): bleeding from the cord, gut, nose or skin. More likely if a baby is unwell or slow to start feeding.
- Late (8 days to 6 months, peak 2–8 weeks): the dangerous one. Without vitamin K it affects about 5–20 in 100,000 babies. About 3 in 10 die, and many bleed into the brain. It’s more likely in exclusively breastfed babies and babies with liver problems.
Rare, but when it happens it often happens in the brain, with little warning.
Your options at birth
Both work. The injection works best and only needs doing once.
- RecommendedOne injection at birth1 mg into the thigh muscle soon after birth (0.5 mg for babies under 1.5 kg).
- Works
- The most reliable option: fewer than 0.3 late bleeds per 100,000 babies
- Cost
- Free in Australian hospitals
- How long
- One dose
- Watch for
- A moment of crying and maybe a small bruise
One jab, done before the first nappy change.
- AlternativeThree oral doses2 mg by mouth at birth, at the newborn screening test (usually day 3–5), and in week four.
- Works
- Less reliable: about 2.5 late bleeds per 100,000 babies in Australia, higher if a dose is missed
- Cost
- Free
- How long
- Three doses over 4 weeks. The third must be given by 4 weeks of age
- Watch for
- Repeat a dose if your baby vomits within an hour. Mostly formula-fed babies don’t need the third dose. A sick baby who can’t take doses by mouth should have the injection
Works if all three happen. Put the week-four dose in your phone now.
Save your worry
Common concerns, and what the evidence says.
- “The injection causes leukaemia”This came from a 1992 study. Later, better-quality studies didn’t confirm it. Australian colleges of paediatrics, obstetrics, general practice and midwifery all recommend vitamin K at birth.
- “A natural birth or eating greens in pregnancy is enough”Neither reliably raises a baby’s vitamin K. Babies are low regardless of how they’re born.
- “Bleeding would be obvious, so we’d catch it”Late bleeding often starts in the brain. Warning signs can be subtle, like a sleepy, pale or poorly feeding baby.
- Vitamin K2 supplements for adult bones or arteriesTrials on bone density and fractures are mixed, and the heart evidence is early. Not a proven fix for people who aren’t deficient.
Adults: who runs low
- Poor absorption: coeliac disease, inflammatory bowel disease, liver or bile duct disease, cystic fibrosis, or after weight-loss surgery.
- Long courses of broad-spectrum antibiotics, especially with poor eating.
- Very poor intake, prolonged fasting or long-term intravenous feeding.
- Warfarin, which works by blocking vitamin K. That’s the point of the drug, not a deficiency.
The main sign is easy bruising or bleeding (gums, nose, heavy periods, blood in urine or stool). A blood clotting test (INR) shows it. Treatment is vitamin K by mouth or injection, plus fixing the cause. Australian adults need about 70 micrograms a day (men) and 60 (women), easily met by leafy greens, broccoli, Brussels sprouts and canola or soybean oil.
If you take warfarin
- Don’t avoid greens. Keep your vitamin K intake steady from week to week.
- A sudden jump (a new green-smoothie habit) can make warfarin work less well. A sudden drop (a week of no veg) can make it work too strongly.
- Check with your doctor or pharmacist before starting any supplement, including multivitamins.
- Newer blood thinners (apixaban, rivaroxaban, dabigatran) don’t work through vitamin K, so diet doesn’t affect them in the same way.
See your GP if
- You’re pregnant and take seizure medicines, rifampicin or warfarin: tell your maternity team so your baby’s vitamin K can be planned
- Your baby had oral vitamin K and missed a dose
- Your baby has yellow skin or eyes after 2 weeks, pale stools or dark urine (possible liver problems, which raise bleeding risk)
- You bruise or bleed easily, especially with a bowel, liver or absorption problem
- You take warfarin and plan a big change in diet
Call 000 (or your local emergency number) if a baby has bleeding that won’t stop, blood in vomit or nappies, a seizure, is unusually sleepy or floppy, vomits repeatedly or has a bulging soft spot. Seek same-day care for unexplained bruising or a nosebleed in a baby under 6 months.
Common questions
Why do newborn babies need vitamin K?
Babies are born with very little vitamin K. It crosses the placenta poorly, a newborn’s gut doesn’t yet have the bacteria that make it, and breast milk contains only small amounts. Without it, blood doesn’t clot properly, and a small number of babies bleed, sometimes into the brain.
What is vitamin K deficiency bleeding (VKDB)?
Bleeding in a baby caused by too little vitamin K. Early VKDB happens in the first 24 hours, classic VKDB in the first week, and late VKDB from 8 days to 6 months, most often at 2 to 8 weeks. Late VKDB is the most dangerous: without vitamin K it affects about 5 to 20 in 100,000 babies, about 3 in 10 of them die, and many bleed into the brain.
Does the vitamin K injection cause cancer?
No link has been confirmed. A 1992 study raised the worry about childhood cancer, but later, better-quality studies did not confirm it. Australia’s NHMRC, the RACP, RANZCOG, the RACGP and the Australian College of Midwives all recommend vitamin K at birth.
Is the injection or oral vitamin K better?
A single injection at birth is the most reliable, with fewer than 0.3 cases of late bleeding per 100,000 babies. Three oral doses also work, but less well (about 2.5 per 100,000 in Australia), and all three doses must be given on time. The injection is the preferred option.
When are the oral vitamin K doses given?
Three doses of 2 mg: at birth, at the newborn screening test (usually day 3 to 5), and in week four. The third dose must be given no later than 4 weeks after birth. Repeat a dose if the baby vomits within an hour. Mainly formula-fed babies don’t need the third dose.
Do adults get low vitamin K?
Rarely from diet alone. It’s more likely with poor absorption (coeliac disease, inflammatory bowel disease, liver or bile duct disease, after weight-loss surgery), long courses of broad-spectrum antibiotics, very poor intake, or long-term intravenous feeding. The main sign is easy bruising or bleeding.
Can I eat leafy greens on warfarin?
Yes. The key is to keep your vitamin K intake steady from week to week, not to avoid it. A sudden big increase can make warfarin work less well; a sudden drop can make it work too strongly. Tell your doctor before changing your diet or starting supplements.
Do vitamin K2 supplements help bones or the heart?
Not proven. Trials on bone density and fractures are mixed, and the evidence on heart disease and artery calcium is early. In Japan a very high-dose form is used as an osteoporosis medicine, but that isn’t the same as an over-the-counter supplement.
Weird history
- In 1929, Danish scientist Henrik Dam noticed chicks on a fat-free diet started bleeding. He named the missing factor the “coagulation vitamin”: vitamin K. He shared the 1943 Nobel Prize with Edward Doisy, who worked out its chemistry.
- Warfarin began with cattle bleeding to death after eating mouldy sweet clover hay in 1920s North America. Karl Paul Link’s lab isolated the culprit in 1939.
- Warfarin is named after the Wisconsin Alumni Research Foundation (WARF), which funded the work. It was sold as rat poison before it was a medicine. US President Eisenhower took it after his 1955 heart attack.
Helpful resources
- Pregnancy, Birth and Baby: Vitamin K at birthPlain-English guide for parents to the injection and oral options. Free, Australia.
- Better Health Channel: Vitamin K and newborn babiesVictorian Government information for parents. Free.
Evidence and more information
- NHMRC, RACP, RANZCOG, RACGP and ACM: Joint statement and recommendations on vitamin K administration to newborn infants
- StatPearls: Vitamin K deficiency
- Nutrient Reference Values for Australia and New Zealand: Vitamin K
- NIH Office of Dietary Supplements: Vitamin K fact sheet
- Nobel Prize: 1943 award ceremony speech (Dam and Doisy)
- Science History Institute: A study in scarlet (the warfarin story)
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