Last reviewed on 11 September 2026.
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This post covers its forms and scientific names, food sources, deficiency in adults, the newborn dose, and blood thinners.
What does vitamin K do in the body?
Its main job is to switch on the proteins that make blood clot. The liver makes clotting factors II (prothrombin), VII, IX and X, and vitamin K adds a chemical tag to each that lets it bind calcium and work. Without enough vitamin K the factors are still made, but they stay inactive and blood clots slowly. The same tagging activates proteins C and S, which keep clotting in check, and bone proteins such as osteocalcin. The letter comes from "Koagulation", the German and Scandinavian spelling, chosen by the Danish scientist Henrik Dam, who discovered it.
What is the scientific name of vitamin K?
Vitamin K is a family, not one compound. Vitamin K1 is phylloquinone, which appears on injection labels as phytomenadione or phytonadione. Vitamin K2 is a group called menaquinones, numbered MK-4 to MK-13 by the length of their side chain; MK-4 and MK-7 are the forms usually sold in supplements. Vitamin K3, menadione, is synthetic and no longer used in human medicine because it can damage red blood cells. All of them share the same ring structure, a naphthoquinone, which is the part that does the chemical work.
| Form | What it is | Where you meet it |
|---|---|---|
| K1 | phylloquinone | green leaves, and injection labels reading phytomenadione or phytonadione |
| K2 | menaquinones, MK-4 to MK-13 | fermented and animal foods, and supplements selling MK-4 or MK-7 |
| K3 | menadione, synthetic | no longer used in people, because it can damage red blood cells |
All of them share the same naphthoquinone ring, which is the part that does the chemical work.
Which foods provide vitamin K1?
Green leafy vegetables, by a wide margin. Spinach, methi, amaranth, mustard greens, coriander, mint, cabbage, broccoli and lettuce are all rich, and a single katori of cooked palak or methi can supply several times the daily adequate intake. Some vegetable oils, including soybean and rapeseed oil, contribute smaller amounts. Because phylloquinone is bound tightly inside the green parts of the plant and is fat-soluble, the body absorbs only a modest share from raw greens; cooking them with a little oil improves the yield.
Which foods provide vitamin K2?
Fermented foods and some animal foods. Natto, a Japanese fermented soybean dish, is by far the richest known source. Hard and soft cheeses, egg yolk, chicken, liver and butter contain smaller amounts. Data on Indian fermented foods such as idli and dosa batter, dhokla or fermented bamboo shoot are scarce, so it is honest to say their K2 content is not well measured. Bacteria in the large intestine also make menaquinones, but how much of that the body absorbs and uses is uncertain. The post on gut health basics explains what those bacteria are known to do.
How much vitamin K do adults need?
Around 90 to 120 mcg a day. US guidance sets an adequate intake of 120 mcg for men and 90 mcg for women, and no upper limit has been set because vitamin K from food and standard supplements has not been shown to cause toxicity. The body also recycles vitamin K through a chemical loop in the liver, so each molecule is reused many times, which is part of why needs are so small. Someone who eats green vegetables a few times a week, alongside dairy and eggs, is very likely above the target already.
What causes vitamin K deficiency in adults?
Rarely the diet alone. Deficiency in adults usually follows a problem with fat absorption, such as coeliac disease, Crohn's disease, chronic pancreatitis, cystic fibrosis, a blocked bile duct or bariatric surgery. Long courses of broad-spectrum antibiotics can contribute, especially in someone who is also eating very little. Liver disease causes bleeding problems of a similar kind because a damaged liver cannot make clotting factors even with enough vitamin K. Warfarin and acenocoumarol create the same effect on purpose, by blocking the vitamin's recycling.
What are the signs of vitamin K deficiency?
Bleeding that is out of proportion to the cause. Typical signs are bruising from minor knocks, gums that bleed on brushing, nosebleeds, unusually heavy periods, blood in the urine (pink, red or brown), black or bloody stools, and cuts or injection sites that keep oozing. A blood test called the prothrombin time, reported as the INR, comes back prolonged. None of these signs is specific: low platelets, inherited clotting disorders, liver disease and some blood cancers cause the same picture. Unexplained bleeding is a reason to see a doctor and get tested, not to buy a vitamin K supplement.
Why do newborn babies need a vitamin K injection?
Because every baby is born with very low vitamin K stores and cannot build them quickly. Little vitamin K crosses the placenta, the newborn gut has not yet been colonised by the bacteria that make menaquinones, and breast milk contains only small amounts. Formula is fortified, so exclusively breastfed babies are the ones most at risk. Without a dose at birth, a small number of babies develop vitamin K deficiency bleeding, which was once called haemorrhagic disease of the newborn. A single injection at birth prevents almost all of it.
What is vitamin K deficiency bleeding in babies?
It is spontaneous bleeding caused by a lack of working clotting factors, and it comes in three patterns. Early bleeding appears in the first 24 hours, mostly in babies whose mothers took certain medicines in pregnancy, including some anti-seizure and tuberculosis drugs. Classic bleeding appears between days two and seven, from the cord stump, gut or nose. Late bleeding appears from about two weeks up to six months, almost entirely in breastfed babies who did not receive vitamin K, and a large share of these cases bleed into the brain, often with no warning. The US CDC reports that babies who miss the birth dose are many times more likely to suffer this late form.
What dose of vitamin K is given to newborns in India?
Indian newborn care guidance recommends vitamin K for every baby, commonly 1 mg injected into the thigh muscle soon after birth, with a smaller dose for very small preterm babies. Oral drops used in some countries need several doses and protect less well if any are missed. Parents should accept it and ask the paediatrician any questions they have, ideally before delivery. If a baby is born at home, make sure the dose is given at the first health visit. A 1990s British report suggesting a link with childhood cancer was not confirmed by the larger studies that followed.
The newborn dose, in order
Ask before the delivery
Raise it with the paediatrician in advance, so the question is settled before the first hour after birth rather than during it.
One injection into the thigh
Indian newborn care guidance recommends it for every baby, commonly 1 mg soon after birth, with a smaller dose for very small preterm babies.
Oral drops are the weaker option
Where drops are used instead, several doses are needed and the protection falls away if any of them are missed.
A home birth needs a plan
If the baby is born at home, make sure the dose is given at the first health visit rather than quietly skipped.
Know what a missed dose risks
Late bleeding appears from about two weeks up to six months, almost entirely in breastfed babies who had no dose, and often begins in the brain without warning.
What is a vitamin K injection used for in adults?
Mainly to reverse the effect of warfarin or acenocoumarol when the INR has climbed too high or bleeding has started, always under medical care. It is given by mouth or slowly into a vein, because rare but severe allergic reactions can follow a fast intravenous dose. Doctors also use it to treat deficiency caused by malabsorption or bile duct blockage, and for poisoning with rat poisons that act like warfarin, which needs prolonged treatment. It does not reverse the newer oral blood thinners such as dabigatran, rivaroxaban or apixaban, which have their own antidotes.
Should you stop eating greens if you take warfarin?
No. Keep your intake steady instead. Warfarin works by blocking vitamin K's recycling, and the dose is set against the INR your usual diet produces. A sudden change moves the INR: a week of methi paratha every morning in winter, a green juice cleanse, or dropping greens during an illness. So the advice is to eat a similar amount of green vegetables from week to week, and to tell the doctor before a big diet change or before starting any supplement, including multivitamins that contain vitamin K. The newer blood thinners are not affected by vitamin K intake in this way.
Are vitamin K2 supplements worth taking for bones or the heart?
The evidence is limited. Japan approved a high-dose form of MK-4, menatetrenone, as an osteoporosis treatment, but trials elsewhere have given mixed results for bone density and fractures. For artery calcification and heart disease, the studies so far are small and short, and mostly measure markers in the blood rather than heart attacks or deaths. Anyone on warfarin must not start K2 without the prescriber's involvement. For bone, calcium, vitamin D, adequate protein and weight-bearing activity carry far more evidence, and the post on calcium-rich Indian foods is the better starting point.
How does vitamin K fit into a child's diet after infancy?
Once solids are established, children get enough from greens, dairy, eggs and their growing gut bacteria, and deficiency beyond infancy is rare unless a child has a malabsorption problem or liver disease. The child nutrition diet chart gives age-wise portions, and the list of all 13 vitamins places K alongside the others. NNWA's Child Nutrition course spends five weeks on feeding children and older adults, including the deficiencies both groups tend to develop, for 8,999 rupees with an NNWA certificate.
In short
Vitamin K, chiefly phylloquinone from leafy greens and menaquinones from fermented and animal foods, activates the proteins that clot blood. Healthy adults rarely lack it, so bleeding and bruising point to malabsorption, liver disease or medicines, and need a doctor. Newborns are the exception, and the single injection at birth is one of the simplest protections a baby can get.