Vitamin K

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By Nikola · Precision Nutrition L1 · Updated 5 November 2026

Vitamin K is a group of fat-soluble vitamins that your body needs to make blood-clotting proteins and certain bone proteins; K1 (phylloquinone) comes mainly from green leafy vegetables, and K2 (menaquinones) from fermented foods, animal foods and gut bacteria. EFSA sets an adequate intake of 70 µg a day for all adults, including pregnant and breastfeeding women, based on 1 µg per kilogram of body weight. Neither the EU nor the US has set an upper limit. One cup of raw spinach or ten sprigs of parsley covers the day. The main safety issue is for people on warfarin, who need to keep their vitamin K intake steady.

What vitamin K does

Vitamin K is a coenzyme for a reaction called gamma-carboxylation, which activates certain proteins. These include prothrombin and other clotting factors, and bone and blood vessel proteins such as osteocalcin and matrix Gla protein (NIH ODS).

K1 and K2 are not the same thing:

• K1, phylloquinone, is made by plants and is the main form in the diet. It is bound to the chloroplasts in leaves, so only part of it is absorbed: the body gets about 4% to 17% as much from spinach as from a tablet. Eating greens with some fat improves absorption.
• K2, menaquinones, range from MK-4 to MK-13. MK-7 is found in natto, a fermented soybean food, and in other fermented foods such as cheese; amounts depend on the bacteria and how the food is fermented. MK-4 is found in modest amounts in meat, dairy and eggs, and the body can also make it from K1. Gut bacteria make most menaquinones, especially the long-chain forms.

EFSA’s intake value covers phylloquinone only, because it found the evidence on menaquinones too limited to set a value for them.

The EU allows these health claims for foods that are at least a source of vitamin K (Regulation (EU) 432/2012):

• “Vitamin K contributes to normal blood clotting”
• “Vitamin K contributes to the maintenance of normal bones”

How much you need a day

Group	EFSA adequate intake (AI), µg/day	EFSA upper limit	For reference: NIH AI, µg/day
Men	70	not set	120
Women	70	not set	90
Pregnancy	70	not set	90
Breastfeeding	70	not set	90
Children	12 (1-3 years) to 65 (15-17 years); 10 for infants 7-11 months	not set	30 (1-3 years) to 75 (14-18 years)

Sources: EFSA 2017 (adequate intake, phylloquinone), EFSA Overview on Tolerable Upper Intake Levels (no upper limit, from the 2003 assessment), NIH ODS. EFSA uses 1 µg per kg of body weight for every age group. The US Food and Nutrition Board set no upper limit either, noting that no adverse effects from vitamin K in food or supplements have been reported.

Best food sources

Food	Vitamin K1, 100 g	Portion	Vitamin K1 per portion
Parsley, fresh	1,640 µg	10 sprigs, 10 g	164 µg
Swiss chard, raw	830 µg	1 cup, 36 g	299 µg
Brussels sprouts, raw	177 µg	1 cup, 88 g	156 µg
Spinach, raw	483 µg	1 cup, 30 g	145 µg
Broccoli, raw	102 µg	1 cup chopped, 91 g	93 µg
Kale, raw	390 µg	1 cup, 21 g	82 µg
Cabbage, raw	76 µg	1 cup chopped, 89 g	68 µg
Romaine lettuce, raw	102 µg	1 cup shredded, 47 g	48 µg
Avocado	21 µg	half an avocado, about 100 g	21 µg
Olive oil	60.2 µg	1 tbsp, 13.5 g	8 µg

Source: USDA FoodData Central, SR Legacy, checked 5 November 2026, vitamin K (phylloquinone): parsley FDC 170416, Swiss chard FDC 169991, Brussels sprouts FDC 170383, spinach FDC 168462, broccoli FDC 170379, kale FDC 168421, cabbage FDC 169975, romaine FDC 169247, avocado FDC 171705, olive oil FDC 171413. Portions are USDA household measures; half an avocado is calculated from USDA’s 201 g whole fruit. Values per portion are calculated and rounded. For K2, NIH lists natto at about 850 µg of MK-7 per 85 g.

Green leaves are the easy win. A cup of raw spinach gives twice EFSA’s 70 µg, and so do ten sprigs of parsley. Chard, Brussels sprouts, broccoli, kale, cabbage and romaine all count. A dressing with olive oil or some avocado adds a little vitamin K and the fat that helps you absorb it. Ideas: kale, apple and walnut salad, pomegranate, walnut and parsley salad or an autumn minestrone with pumpkin and cabbage.

Deficiency: signs and who is at risk

In adults, vitamin K deficiency is very rare and usually comes from poor absorption or medicines that interfere with vitamin K. The main sign is bleeding (NIH ODS).

• Newborn babies are the exception. Little vitamin K crosses the placenta, and babies can develop vitamin K deficiency bleeding, early in the first week or late at 2 to 12 weeks, the late form mostly in exclusively breastfed babies. Late bleeding can affect the brain. This is why newborns are given vitamin K1 at birth; the American Academy of Pediatrics recommends a single injection of 0.5-1 mg.
• Malabsorption: cystic fibrosis, coeliac disease, ulcerative colitis and short bowel syndrome.
• After bariatric surgery, when vitamin K status may need monitoring.

Supplements: when they make sense

Most people get enough from vegetables, and multivitamins usually contain modest amounts. Supplements use phytonadione (synthetic K1), MK-4 or MK-7; menadione (K3) damaged liver cells in lab studies and is no longer used in supplements (NIH ODS).

• Bones. The evidence is mixed. A 2006 meta-analysis, mostly of Japanese trials using 45 mg a day of MK-4, found fewer fractures, but later trials in older adults found no effect on bone density.
• Heart and arteries. In observational studies, more dietary menaquinone, but not phylloquinone, is linked with less calcification in the arteries. Trials are inconclusive: 500 µg of phylloquinone a day for 3 years made no overall difference to coronary calcification.
• Dose. The NHS says 1 mg or less a day from supplements is unlikely to cause harm.

If you take any blood-thinning medicine, do not start a vitamin K supplement on your own: see below.

Who should be careful

• Warfarin and similar anticoagulants. Vitamin K can seriously interact with these medicines. NIH advises keeping your intake from food and supplements consistent, because sudden changes can raise or lower the drug’s effect. MedlinePlus lists broccoli, Brussels sprouts, raw cabbage, kale, collard greens, spinach, lettuce, parsley and some oils among foods to keep steady. You do not have to stop eating greens: eat similar amounts week to week and talk to your doctor before any supplement.
• Newer anticoagulants. Ask your doctor or pharmacist whether diet matters for your specific medicine; the advice above is written for warfarin.
• Antibiotics. They can kill the gut bacteria that make vitamin K, which matters mainly with courses longer than several weeks and a poor diet; some cephalosporins may also block its action.
• Other medicines. Bile acid sequestrants (cholestyramine, colestipol) and orlistat reduce vitamin K absorption; orlistat taken with warfarin can change clotting times.
• High-dose vitamin E. Large doses of vitamin E may increase bleeding risk in people on anticoagulants, especially when vitamin K intake is low.

FAQ

What is the difference between vitamin K1 and K2?

K1 (phylloquinone) comes from green plants and is the main form in most diets. K2 (menaquinones, such as MK-4 and MK-7) comes from fermented foods like natto and cheese, from meat, dairy and eggs, and from gut bacteria. EFSA’s intake value of 70 µg a day covers K1 only.

Can I eat leafy greens if I take warfarin?

Yes. The advice from NIH and MedlinePlus is to keep your vitamin K intake consistent, not to avoid it. Sudden big changes, such as starting a daily spinach smoothie, can change how warfarin works, so tell your doctor before you change your diet or take a supplement.

What foods are high in vitamin K?

Green leafy vegetables and herbs. Per 100 g, fresh parsley has 1,640 µg, Swiss chard 830 µg, spinach 483 µg and kale 390 µg of K1 (USDA). For K2, natto is the richest food, with about 850 µg of MK-7 in an 85 g serving (NIH).

Related entries and articles

• Spinach, kale and chard
• Parsley, broccoli and Brussels sprouts
• Cabbage and collard greens
• Vitamin E – and why high doses matter for clotting
• Vitamin D and vitamin A – the other fat-soluble vitamins
• Kale, apple and walnut salad
• Pomegranate, walnut and parsley salad
• Autumn minestrone with pumpkin and cabbage

Sources

1. USDA FoodData Central, SR Legacy: Parsley, fresh (FDC 170416); Chard, swiss, raw (FDC 169991); Spinach, raw (FDC 168462); Kale, raw (FDC 168421). fdc.nal.usda.gov
2. USDA FoodData Central, SR Legacy: Brussels sprouts, raw (FDC 170383); Broccoli, raw (FDC 170379); Cabbage, raw (FDC 169975); Lettuce, cos or romaine, raw (FDC 169247). fdc.nal.usda.gov
3. USDA FoodData Central, SR Legacy: Avocados, raw, all commercial varieties (FDC 171705); Oil, olive, salad or cooking (FDC 171413). fdc.nal.usda.gov
4. NIH Office of Dietary Supplements: Vitamin K, Fact Sheet for Health Professionals. ods.od.nih.gov
5. NIH Office of Dietary Supplements: Vitamin E, Fact Sheet for Health Professionals (interaction with anticoagulants). ods.od.nih.gov
6. EFSA NDA Panel (2017). Dietary reference values for vitamin K. EFSA Journal 15(5):4780. efsa.europa.eu
7. EFSA: Overview on Tolerable Upper Intake Levels, version 11 (August 2025). efsa.europa.eu
8. Commission Regulation (EU) No 432/2012 – permitted health claims. eur-lex.europa.eu
9. MedlinePlus: Taking warfarin. medlineplus.gov
10. NHS: Vitamin K. nhs.uk

This page is for information only and is not medical or dietary advice.