What is vitamin K2 for?

Bone is where it has its best data: 180 micrograms of MK-7 a day for three years slowed part of the bone density loss in the lumbar spine and femoral neck in healthy postmenopausal women, though not in the total hip. Beyond that, vitamin K is needed for blood clotting.

K1 or K2, MK-4 or MK-7?

K1 comes mainly from leafy greens and K2 from fermented foods and animal products. Within K2, MK-7 has a longer half-life and more potency than MK-4, and it is the form used in the three-year low-dose trial.

Can K2 be taken with anticoagulants?

Not on your own. Anticoagulants like warfarin or acenocoumarol work precisely by antagonising vitamin K, so adding vitamin K directly interferes with the treatment. The prescribing doctor decides.

Do you need to take K2 with vitamin D?

It is the usual sales argument, directing calcium to bone instead of arteries. The three-year trial with a result used MK-7 alone, so what is proven is K2’s effect on bone density, not the synergy of the bundle.

Home / Vitamin K2 / Guide

Vitamin K2 · Moderate evidence

What vitamin K2 is for and how much to take

The short answer. Vitamin K is needed for blood clotting and for bone, and that second function has a health claim recognised under European regulation. K2 as MK-7 is the form sold as a supplement, and its best trial lasted three years: in postmenopausal women, 180 micrograms a day slowed part of the bone density loss in the lumbar spine and femoral neck, but not the total hip. It is a real, limited result. What does not exist is sports evidence, and what does exist is a serious interaction with anticoagulants.

There are studies in favour, but few, with small samples or measuring markers instead of outcomes. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of vitamin K2 with their source
Effect	How much	Detail
Bone density in spine and femoral neck	less loss at 3 years	With 180 micrograms of MK-7 a day in 244 healthy postmenopausal women. It slows the age-related decline; it does not rebuild lost bone. [2]
Total hip bone density	no effect	The same trial found no effect there. A supplement that works at some sites and not others should be reported in full, not just the good half. [2]
Vitamin K status	marker improves	The ratio of uncarboxylated to carboxylated osteocalcin improved significantly. That is the marker, not the clinical outcome. [2]
Nutrient reference value	75 µg	The European labelling figure for vitamin K. MK-7 supplements usually contain between 45 and 200 micrograms. [1]
Fractures	not the measured outcome	The trial measured bone density, femoral strength indices and vertebral height loss, not fracture incidence as its main outcome. That is the leap marketing usually makes. [2]

02 How to take it

Dose. 180 micrograms of MK-7 a day, the dose from the three-year trial.
When. With a meal containing fat, because it is fat-soluble.
How long before you notice it. The trial measured at one, two and three years. This is a timescale of years, not weeks.

Details that change the result

MK-7 and MK-4 are not the same: MK-7 has a longer half-life and more potency, and it is the one used in the three-year low-dose trial.
With vitamin K antagonist anticoagulants, such as warfarin or acenocoumarol, do not touch this without your doctor: vitamin K is exactly what that drug antagonises.
It is sold together with vitamin D on the argument that it directs calcium to bone. The MK-7 trial used MK-7 alone, so what is proven is what was tested.
There is no evidence that it improves sports performance. It sits in sports supplement catalogues out of commercial habit, not data.

03 When it makes sense and when it does not

Worth it if

Postmenopausal women concerned about bone density loss, understanding that the measured effect is slowing part of the decline over three years.
With a diet very low in leafy greens and fermented foods.

Not worth it if

While taking vitamin K antagonist anticoagulants, unless explicitly advised by a doctor.
Expecting an effect on performance, strength or body composition.
Expecting results in weeks: the only trial with a relevant result lasted three years.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Reglamento (UE) 1169/2011 sobre la informacion alimentaria facilitada al consumidor, Anexo XIII: valores de referencia de nutrientes. Vitamina K, 75 ug. Es un valor de ETIQUETADO, no una dosis con efecto demostrado. https://eur-lex.europa.eu/legal-content/ES/TXT/?uri=CELEX%3A32011R1169
Knapen MHJ, Drummen NE, Smit E, Vermeer C, Theuwissen E. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499-2507. 244 mujeres posmenopausicas sanas, 180 ug/dia de MK-7 durante 3 anos: menor descenso asociado a la edad del contenido y la densidad mineral osea en columna lumbar y cuello femoral, sin efecto en cadera total, y mejora del estado de vitamina K medido por el cociente de osteocalcina sin carboxilar. doi:10.1007/s00198-013-2325-6

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about vitamin K2

Answered with the data on this page

What is vitamin K2 for?: Bone is where it has its best data: 180 micrograms of MK-7 a day for three years slowed part of the bone density loss in the lumbar spine and femoral neck in healthy postmenopausal women, though not in the total hip. Beyond that, vitamin K is needed for blood clotting.
K1 or K2, MK-4 or MK-7?: K1 comes mainly from leafy greens and K2 from fermented foods and animal products. Within K2, MK-7 has a longer half-life and more potency than MK-4, and it is the form used in the three-year low-dose trial.
Can K2 be taken with anticoagulants?: Not on your own. Anticoagulants like warfarin or acenocoumarol work precisely by antagonising vitamin K, so adding vitamin K directly interferes with the treatment. The prescribing doctor decides.
Do you need to take K2 with vitamin D?: It is the usual sales argument, directing calcium to bone instead of arteries. The three-year trial with a result used MK-7 alone, so what is proven is K2’s effect on bone density, not the synergy of the bundle.

And now, which to buy

Prices, kept apart from the evidence

This page explains what vitamin K2 does and deliberately names no brand. The comparison is the other half: 21 products from 4 stores from €0.092 per capsule, sorted by price and by how verifiable their certification is.

See the vitamin k2 comparison

Other guides

What each supplement does, with its sources