Vitamin K2 MK-7 vs MK-4: Which Form Should You Take?

Vitamin K2 has gone from an obscure nutrient to a staple in bone and heart health stacks, often taken alongside vitamin D. But walk down the supplement aisle and you'll see two different forms on labels: MK-4 and MK-7. They're both vitamin K2, yet they behave very differently in the body. Understanding vitamin K2 MK-7 vs MK-4 is the difference between a dose that shows up in your bloodstream and one that largely doesn't.

Here's what each form is, what the research says about absorption and dosing, where the evidence is strong and where it's still mixed, and how to choose.

What Vitamin K2 Does

Vitamin K is a family of compounds. Vitamin K1 (phylloquinone) comes mostly from leafy greens and is primarily used by the liver for normal blood clotting. Vitamin K2 (menaquinones) comes from fermented and animal foods and is more associated with tissues outside the liver.

All forms of vitamin K act as a cofactor that "switches on" specific proteins. Two matter most for this discussion:

• Osteocalcin is made in bone and is involved in bone mineralization.
• Matrix Gla protein (MGP) is found in blood vessel walls, bone and cartilage, and is involved in regulating where calcium is deposited.

When vitamin K status is low, these proteins stay in an inactive, "undercarboxylated" form. Researchers have linked that state to lower bone density in some studies, which is a big reason K2 has drawn so much interest.

The NIH sets an Adequate Intake for vitamin K at 120 mcg per day for adult men and 90 mcg for adult women. Those numbers are based on vitamin K1 intake and clotting, not on optimizing K2 status.

Vitamin K2 MK-7 vs MK-4: The Key Differences

MK-4 (menaquinone-4)

MK-4 is a short-chain form found in animal foods like egg yolks, butter and meat. Your body can also make MK-4 from vitamin K1. Most of the clinical research on MK-4 comes from Japan and used pharmacological doses of 15 to 45 milligrams per day, dozens to hundreds of times the amount in typical MK-7 supplements.

MK-7 (menaquinone-7)

MK-7 is a long-chain form found mainly in natto, a traditional Japanese fermented soybean food, and in smaller amounts in some cheeses. Natto is the richest known source: about 850 mcg of MK-7 per 3-ounce serving, according to the NIH. Supplements usually provide 90 to 200 mcg.

The absorption study that shaped the debate

In a 2012 study in Nutrition Journal, researchers gave healthy young women a single 420 mcg dose of either MK-4 or MK-7 with breakfast. MK-7 was well absorbed, peaked about six hours later and was still detectable 48 hours after dosing. MK-4 was not detectable in the blood at any time point. In a second phase, 60 mcg per day for seven days raised blood MK-7 levels in every participant, while MK-4 produced no increase.

The study was small, with five women per group, but it explains a lot: at the microgram doses found in most supplements, MK-7 actually reaches the bloodstream and builds up over time, while MK-4 needs far larger doses to have an effect.

What the Research Says About K2 and Bone Health

The best-known MK-7 trial was published in Osteoporosis International in 2013. Researchers gave 244 healthy postmenopausal women 180 mcg of MK-7 or a placebo daily for three years. The MK-7 group showed favorable changes in bone mineral content, bone mineral density at the lumbar spine and femoral neck, and calculated bone strength compared with placebo. The trial was sponsored by the ingredient supplier, which is worth noting.

The NIH describes the broader picture as mixed. Some studies link higher vitamin K intake to better bone measures; others find no benefit, and calcium and vitamin D taken alongside can muddy the results. K2 is a reasonable part of a bone-health routine, but it works best alongside the fundamentals: adequate calcium and vitamin D, enough protein, and resistance training.

What About K2 and Heart Health?

This is where you'll see the boldest claims online, so let's be precise. Observational studies from the Netherlands found that people who ate more menaquinones (K2) tended to have better cardiovascular measures. Because MGP is found in blood vessel walls, there's a plausible mechanism for K2 to support healthy blood vessels.

However, observational studies can't prove cause and effect, and the NIH describes the randomized trial evidence on vitamin K and blood vessel outcomes as limited and inconsistent so far. The honest summary: K2 supports normal calcium metabolism and is a sensible part of a long-term cardiovascular wellness routine, but the research is still developing. For a broader look at everyday habits that matter for your circulation, read 6 ways to care for your heart and blood flow now.

How to Take Vitamin K2

• Choose MK-7 if you want an efficient, once-daily microgram dose.
• Take it with a meal that contains fat. Vitamin K is fat-soluble.
• Pair it with the basics. Vitamin D, calcium from food, protein and strength training all work together for bone health.
• Be consistent. MK-7 builds up in the blood over days of regular use.
• Check medications first. Vitamin K directly affects warfarin and similar anticoagulants. If you take one, don't start K2 without your doctor's guidance.

Where PureBlood Fits

PureBlood was built around the form the research favors. Each 4-capsule serving delivers 200 mcg of vitamin K2 as K2VITAL® MK-7, alongside 2,000 mg of Citrus Bergamot and 10,800 FU of Nattiase® Nattokinase, for a once-daily formula designed to support circulation, healthy calcium metabolism and cardiovascular wellness. According to CleanForm, it's non-GMO, vegetarian and free of artificial additives. Note that it is soy-derived. For a deeper look at the full formula, see our breakdown of all three PureBlood ingredients.

Vitamin K2 FAQ

Is MK-7 better than MK-4?

For typical supplement doses, MK-7 has the advantage. It's absorbed well, stays in the blood for days and raises blood levels at microgram doses. MK-4 research generally relies on much larger milligram doses.

How much vitamin K2 should I take per day?

There's no official K2-specific recommendation. Most MK-7 research and supplements use 90–200 mcg per day, and the 3-year bone trial used 180 mcg.

Should I take vitamin K2 with vitamin D?

They're commonly paired because both are involved in calcium metabolism, and many people take them together. Taking both with a meal containing fat is a practical approach.

Who should avoid vitamin K2?

Anyone taking warfarin or similar vitamin K antagonist blood thinners should not start K2 without medical supervision, because changes in vitamin K intake affect how those drugs work. If you're pregnant, nursing or managing a health condition, check with your healthcare provider.

The Bottom Line

In the vitamin K2 MK-7 vs MK-4 debate, MK-7 wins on practicality: it absorbs well, lingers in the blood and works at small daily doses, which is why it's the form used in most modern research and supplements. The bone data is encouraging, the heart data is still evolving, and K2 works best as part of a bigger routine built on good food and training. If you want MK-7 in a once-daily circulation formula, PureBlood delivers 200 mcg of K2VITAL® MK-7 per serving.

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Sources: Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. 2012. · Knapen MHJ, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013. · NIH Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement.