Vitamin K2: What It Does, MK-7 vs MK-4 & How Much (2026)
By Erin Rose Updated October 5, 2026 Sources
Vitamin K2 is a form of vitamin K made by bacteria. Natto is by far the richest food; cheese, eggs and meat hold small amounts. Most U.S. diets have enough vitamin K. Trials of K2 pills on bone and arteries are mixed. If you take warfarin, don’t take K2 unless your doctor says so.
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What vitamin K2 is
Vitamin K comes in two main types. K1 comes from leafy greens. K2 is a family of forms made mostly by bacteria, found in fermented and animal foods (NIH). The two K2 forms on labels are MK-7 and MK-4.
- What it does. Your body needs vitamin K, K1 or K2, to activate proteins for blood clotting, osteocalcin in bone and matrix Gla protein in blood vessels (Schurgers 2007). The idea that low vitamin K lets calcium build up in arteries comes largely from animal studies; in people it is still a hypothesis (NIH).
- MK-7 vs MK-4. MK-7 stays in the blood much longer; at the same small dose, MK-4 did not show up in the blood at all (Sato 2012). MK-7 vs MK-4.
- How much you need. Adults need 90 mcg (women) or 120 mcg (men) of vitamin K a day, K1 and K2 together; most U.S. diets have enough (NIH). There is no separate target for K2.
K2 in food
Natto, a Japanese fermented soybean food, holds about 850 mcg of MK-7 in 3 ounces. The next richest food on NIH’s list, chicken breast, rotisserie, holds 13 mcg of MK-4. Cheese, eggs and meat hold small amounts.
| Item | Value |
|---|---|
| Natto, 3 ounces | 850 mcg |
| Chicken breast, rotisserie, 3 ounces | 13 mcg |
| Ground beef, broiled, 3 ounces | 6 mcg |
| Chicken liver, braised, 3 ounces | 6 mcg |
| Ham, 3 ounces | 4 mcg |
| Cheddar cheese, 1½ ounces | 4 mcg |
| Egg, hard boiled, 1 large | 4 mcg |
| Mozzarella cheese, 1½ ounces | 2 mcg |
| Milk, 2%, 1 cup | 1 mcg |
What trials found
Here is each common claim, next to the best human trials we found.
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MixedSlowing bone loss
180 mcg of MK-7 a day for 3 years slowed bone loss at the spine and hip neck in 244 healthy women after menopause (Knapen 2013), and 90 mcg of K2 for 1 year slowed hip-neck loss in women after menopause in China (Zhang 2020). Two other trials, at 360 mcg for 1 year and 375 mcg for 3 years, found no effect (Emaus 2010; Rønn 2021). See every trial’s dose.
-
Not shownPreventing fractures
A 2019 review of 36 vitamin K trials, all forms, found no effect on spine fractures after menopause; it may lower clinical fractures, but the evidence is too weak to confirm (Mott 2019). The trials that found fewer fractures were Japanese MK-4 trials, mostly at a 45 mg drug dose, and the review of them included problematic trials (Torgerson 2018). See the MK-4 fracture record.
-
MixedSlowing calcium build-up in arteries
360 mcg of MK-7 a day for 2 years slowed new calcium build-up in the heart arteries of people with heart disease (Vossen 2026). Other trials, in diabetes, on dialysis and in heart-valve disease, found no effect (Zwakenberg 2019; RenaKvit 2021; AVADEC 2022). A 2023 review of 14 trials found a small slowing and called for better trials (Li 2023).
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Not shownRemoving calcium already in arteries
No trial shows K2 removes calcium that is already there. Even in the positive trial, calcium rose in both groups; it rose less with MK-7 (Vossen 2026).
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A link, not proofFewer heart attacks or deaths
In a Dutch study that followed 4,807 older adults for about 7 years, people who ate the most K2, mostly from cheese and meat, were less likely to die of heart disease (Geleijnse 2004). That shows a link, not that K2 caused it. No trial large enough to tell has shown K2 prevents heart attacks or strokes.
- How long trials ran. Bone trials ran 1 to 3 years; the 3-year trial measured bone at 1, 2 and 3 years (Knapen 2013). The artery trial that found slower calcium build-up ran 2 years (Vossen 2026). No trial shows a quick effect.
How much K2 to take
There is no official K2 dose. Most bottles give 100 mcg of MK-7 a day. 90 mcg is the lowest daily dose a trial reported a benefit with, and the 3-year bone trial used 180 mcg. Take it with a meal. Our K2 dosage guide covers every situation.
Side effects and cautions
No upper limit is set for vitamin K (NIH), and a US Pharmacopeia safety review found no serious risk from MK-7 supplements (Marles 2017).
- Warfarin and similar drugs. Don’t start, stop or change K2 unless the doctor who manages it says so. In healthy volunteers on a warfarin-type drug, 45 mcg of MK-7 a day lowered INR by about 40% (Theuwissen 2013). More on blood thinners.
- K blends. Some K2 products add K1 or MK-4 in large amounts; Thorne’s Vitamin K capsule holds 6,090 mcg of vitamin K in all. Read the label if you watch your vitamin K.
Which K2 to buy
Buy a K2 on a public testing list. Only 3 of the 20 K2 products we read are on one, and only one is a plain MK-7: our pick, Nature Made Vitamin K2 100 mcg, at the top of the page. If you want vitamin K1 and MK-4 too:
If price matters most. Horbaach Vitamin K2 MK-7 100 mcg costs $0.062 a day, against $0.70 for our pick, but it is not on a public testing list. Buy Horbaach Vitamin K2 MK-7 100 mcg on Amazon
See all 17 we score, with each score, cost and testing list.
When you don’t need K2
- You take warfarin or a similar blood thinner, unless your doctor says so.
- You already take a vitamin D pill with K2. Count its K2 before you add more. Vitamin D with or without K2.
- You want a sure benefit. The trials are mixed, and none shows K2 prevents fractures or heart attacks.
K2 guides
How much
Which form
Which product
With vitamin D
How we checked this
Products. We read 20 K2 products and could score 17. Scores rebuilt October 5, 2026. Every score, and why some are not scored.
Testing lists. We searched NSF/ANSI 173 by every brand and maker, and read NSF Certified for Sport, Informed Choice and Informed Sport in full, on October 5, 2026. USP’s site blocks automated reads, so its list comes from our earlier copy.
Prices. Each brand’s own list price for one pack. Amazon’s price can differ.
Sources
- NIH Office of Dietary Supplements. Vitamin K fact sheet for health professionals (intakes, food table, upper limit, warfarin, animal-data hypothesis; updated March 29, 2021; read October 5, 2026).
- Knapen MH, et al. Osteoporos Int. 2013. PubMed 23525894. Zhang Y, et al. Calcif Tissue Int. 2020. PubMed 32060566. Emaus N, et al. Osteoporos Int. 2010. PubMed 19937427. Rønn SH, et al. Osteoporos Int. 2021. PubMed 33030563. Mott A, et al. Osteoporos Int. 2019. PubMed 31076817. Torgerson DJ (caution to readers). JAMA Intern Med. 2018. PubMed 29582044.
- Vossen LM, et al. JAMA Cardiol. 2026. PubMed 42268593. Zwakenberg SR, et al. Am J Clin Nutr. 2019. PubMed 31387121. Levy-Schousboe K, et al. (RenaKvit). Clin Kidney J. 2021. PubMed 34476095. Diederichsen ACP, et al. (AVADEC). Circulation. 2022. PubMed 35465686. Li T, et al. Front Nutr. 2023. PubMed 37252246.
- Geleijnse JM, et al. (Rotterdam Study). J Nutr. 2004. PubMed 15514282.
- Schurgers LJ, et al. Blood. 2007. PubMed 17158229. Sato T, et al. Nutr J. 2012. PubMed 23140417.
- Theuwissen E, et al. J Thromb Haemost. 2013. PubMed 23530987. Marles RJ, et al. Nutr Rev. 2017. PubMed 28838081.
This page is for information. It is not medical advice.