How much vitamin K do you need per day?

The Adequate Intake for vitamin K is 120 mcg a day for men and 90 mcg for women aged 19 and over.

These are the reference amounts used on US food labels and in dietary guidance, not personal targets. What you need shifts with age, pregnancy, medication and health conditions. The % Daily Value shown on every food page here is calculated against the FDA Daily Value for vitamin K, which is 120 µg a day.

What this means for you

One hundred and twenty micrograms a day for men and 90 for women, and a single cup of cooked collards or kale blows past it several times over. Spinach, broccoli, chard and other leaves do the same.

Because greens are so concentrated, deficiency from diet alone is rare in adults. When it happens, it usually belongs to someone who cannot absorb fat properly, and the sign is bleeding rather than anything subtle.

No upper limit was set, because vitamin K has low potential for toxicity.

Not for everyone. One group has to read this differently. People taking warfarin or a similar anticoagulant need a steady vitamin K intake, because sudden changes in either direction alter how well the drug works. The rule is consistency, not avoidance, and it includes supplements and green powders.

Whether more than 120 does anything

That is the question the supplement aisle is really asking. Six cohort and case-control studies covering 93,776 people were pooled. People eating more vitamin K had about 17 per cent fewer fractures overall and about 24 per cent fewer hip fractures, and the confidence interval on each of those touches no effect, so neither stands up on its own. The shape of the curve is the useful part. Fracture risk fell as intake rose only up to about 120 micrograms a day, and then it stopped falling.

Unsettled. The trials do not settle it either. A systematic review found 36 of them, and pooling the ones in postmenopausal or already osteoporotic adults, vitamin K looked like it cut clinical fractures by 28 per cent. Keep only the trials at low risk of bias and that effect stops being statistically significant. Vertebral fractures did not move at all. Two years of supplements added 1.63 per cent to bone density at the lumbar spine, which is the sort of difference a scanner can measure without anyone being able to say it prevents a break.

So 120 micrograms is where the food data stops improving, and the trials have nothing extra to offer above it. A portion of greens clears that several times over, which is the whole of the practical advice.

For everyone not on those drugs, there is no counting to do here. Eat greens when you like them, and the requirement takes care of itself.

On the supplement question, two recent results are worth having. In 123 dialysis patients given 360 micrograms of K2 a day for two years, bone density fell faster at the wrist and slower at the spine, and the authors concluded it does not preserve bone. Pooling 14 trials in 1,533 patients, vitamin K did slow the build-up of calcium in coronary arteries, in people who mostly had kidney disease. Neither finding supports buying K2 for a healthy skeleton.

The cup of greens covers the number, and that is not the same thing

The arithmetic above is correct. Raw spinach carries 482.9 micrograms per 100 g, so one cup, about 25 g, comes to 120.7 micrograms, which is the whole daily reference intake. Raw kale is 390 per 100 g, so a cup is 97.5 and one leaf is 39. That is where the reassuring sentence on every vitamin K page comes from.

Unsettled. Then somebody measured what people actually take up. Fed a large serving of kale with oil, which is the most favourable condition anyone has tested, the bioavailability of phylloquinone came out at 4.7 per cent. Under one twentieth of what was on the plate. Plasma peaked between 6 and 10 hours at about 2.1 nmol/L and dropped away quickly, with a half-life of 8.8 hours in plasma against 215 hours in tissue. So the cup of spinach is honest arithmetic and misleading advice. What rescues it is that nobody knows what you actually need, so there is no established gap to worry about. It is still worth knowing that the comfortable sentence was built from the number in the table rather than the number in the person.

Why nobody can say whether you are short

Vitamin K carboxylates a family of proteins. The ones in the liver run blood clotting, and how much vitamin K those need is known, which is where 120 micrograms comes from. The proteins outside the liver are involved in bone and in the calcification of arteries, and how much vitamin K they need to work properly has never been established.

Unsettled. That gap is visible in the national survey. Median intake is 75.4 micrograms a day, 74.5 for men and 76.6 for women. The mean is 120.4 and the 95th percentile is 364.2, which is an extremely lopsided spread driven by whoever happened to eat a salad on the day they were asked. The survey's shortfall table holds no row for vitamin K, because there is no requirement to fall below. This is the one nutrient on this site where the share of people coming up short cannot be calculated at all, and 120 micrograms is an adequate intake rather than a measured requirement.

None of which changes what to do. Eat greens because they are good food. Add some fat to them because it probably helps. Do not treat the number as a target you are passing or failing.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Foods highest in vitamin K on this site

• Collards, frozen, chopped, cooked — 1059.4 µg per 1 cup, chopped (883% DV)
• Collards, cooked, boiled, drained — 772.5 µg per 1 cup, chopped (644% DV)
• Beet greens, cooked, boiled, drained — 697 µg per 1 cup (1" pieces) (581% DV)
• Chard, swiss, cooked, boiled — 572.8 µg per 1 cup, chopped (477% DV)
• Cress, garden, cooked, boiled — 517.6 µg per 1 cup (431% DV)

All vitamin K sources ranked →

Full guide: Vitamin K: the nutrient whose most useful fact is about a medicine