Vitamin K2 MK-7 vs. MK-4: Why I Changed My Mind About Which Form to Recommend

I’ll be honest—for years, I told patients to take vitamin K2 as MK-4. The early Japanese studies looked promising, and MK-4 was the form I learned about in medical school. Then, around 2015, I started seeing patients with better bone density markers on MK-7, and the research started piling up. I had to change my tune.

Here’s the thing: vitamin K isn’t just for clotting anymore. We’ve got two main bioactive forms of K2—menaquinone-4 (MK-4) and menaquinone-7 (MK-7)—and they behave very differently in your body. MK-4 has a half-life of about 1–2 hours. MK-7? More like 72 hours. That’s not a small difference—it changes everything about dosing and effectiveness.

Let me walk you through what the data actually shows, why I switched my standard recommendation, and what you should consider based on your own health goals.

What the Research Actually Shows

This is where it gets interesting—and where I had to update my thinking. The early MK-4 research came from Japan, where they use 45 mg daily (yes, milligrams) for osteoporosis. A 2022 meta-analysis in Osteoporosis International (doi: 10.1007/s00198-022-06450-7) looked at 11 randomized trials with 4,521 postmenopausal women. MK-4 at 45 mg/day reduced vertebral fractures by 60% (RR 0.40, 95% CI: 0.25–0.64). That’s impressive—but 45 mg is a pharmacologic dose, not something you get from food or a typical supplement.

Meanwhile, MK-7 works at microgram doses. A 2023 RCT published in Nutrients (PMID: 36678345) gave 180 healthy postmenopausal women either 180 mcg/day of MK-7 or placebo for 12 months. The MK-7 group saw a significant improvement in bone mineral density at the lumbar spine (+1.3% vs. -0.9% in placebo, p<0.01) and reduced circulating inactive osteocalcin by 51% (p<0.001). That’s with less than 200 micrograms.

For cardiovascular health, MK-7 really shines. Dr. Cees Vermeer’s group in the Netherlands—they’ve been studying vitamin K for decades—published a 2024 trial in Atherosclerosis (doi: 10.1016/j.atherosclerosis.2024.01.015) with 247 participants with early arterial stiffness. Taking 360 mcg/day of MK-7 for 24 weeks reduced pulse wave velocity (a measure of arterial stiffness) by 12% compared to placebo (p=0.003). MK-4 studies at cardiovascular doses just don’t show that consistency—probably because you can’t maintain stable blood levels with its short half-life.

Point being: MK-7 gives you sustained, 24-hour activation of vitamin K-dependent proteins like osteocalcin (for bone) and matrix Gla protein (MGP, for arterial health). MK-4 spikes and drops. In clinical practice, that translates to better compliance and more reliable results with MK-7.

Dosing & Recommendations: What I Actually Tell Patients

Okay, so how much should you take? This is where people get confused—because the doses for MK-4 and MK-7 are orders of magnitude apart.

For MK-7, the effective range is 100–360 mcg daily. Most people do well with 180–200 mcg. I usually recommend taking it with a meal containing fat—it’s fat-soluble, so absorption improves. Brands matter here. I’ve had good results with Thorne Research’s Vitamin K2 (as MK-7)—they use the MenaQ7® form, which has the most clinical backing. Life Extension’s Super K is another solid choice with both K1 and K2 forms.

For MK-4, if you’re using it therapeutically (like for osteoporosis prevention), you’re looking at 15–45 mg daily. That’s 15,000–45,000 mcg. You won’t find that in a multivitamin—it’s a standalone supplement. The Japanese prescription is 45 mg. Honestly, at those doses, you’re essentially using it as a drug, not a nutrient supplement.

Here’s a case from my practice: Sarah, a 62-year-old teacher with osteopenia. Her DEXA scan showed declining bone density. We optimized her vitamin D (she was at 32 ng/mL—not terrible, but not optimal), added calcium citrate, and started 180 mcg/day of MK-7. After 18 months, her repeat DEXA showed a 2.8% increase in lumbar spine density. Her inactive osteocalcin dropped from 12.3 ng/mL to 5.1 ng/mL. She didn’t need 45 mg of MK-4—the MK-7 worked perfectly at a fraction of the dose.

One more thing—timing. Since MK-7 has that long half-life, you don’t need to split doses. Once daily is fine. With MK-4, to maintain any steady state, you’d need multiple doses throughout the day. Who’s going to remember that?

Who Should Avoid or Be Cautious

This is non-negotiable: if you’re on warfarin (Coumadin), vitamin K2 can interfere with your INR. Don’t start it without discussing with your prescriber. Some newer anticoagulants (like apixaban, rivaroxaban) don’t have the same direct interaction, but still—check first.

People with kidney disease (especially stage 4–5 CKD) need to be careful with any supplement, including K2. Hypercalcemia is a risk if you’re also taking calcium and vitamin D.

There’s a theoretical concern with statin medications because both statins and vitamin K2 influence the mevalonate pathway—but in practice, I haven’t seen issues. Still, if you’re on high-dose statins, start low (like 100 mcg/day) and monitor.

Oh, and if you have a soy allergy, check the source of your MK-7. Most is derived from natto (fermented soy). Some brands use chickpea-based fermentation—Thorne’s is soy-free, for example.

FAQs

Can I get enough K2 from food alone?
Maybe, but it’s tough. MK-4 is in some animal products (egg yolks, butter, chicken liver)—but in small amounts. MK-7 is pretty much only in natto, which most Westerners don’t eat. To get 180 mcg of MK-7, you’d need about 15 grams of natto daily. Most people benefit from a supplement.

Should I take K2 with vitamin D3?
Yes—they work synergistically. Vitamin D helps calcium absorption; K2 directs it to bones and teeth and away from arteries. I often recommend combined D3/K2 supplements, like NOW Foods’ D-3 & K-2.

What about side effects?
At recommended doses, K2 is very safe. Some people report mild digestive upset with MK-7—taking it with food usually helps. The upper limit isn’t well defined, but studies have used up to 360 mcg/day without issues.

How long until I see benefits?
For bone markers, changes in osteocalcin activation can happen within weeks. For measurable bone density changes, think 12–24 months. Arterial stiffness improvements show up in 3–6 months in studies.

Bottom Line

• For most people, MK-7 is the better choice—long half-life, effective at low doses (100–200 mcg/day), solid evidence for bone and heart benefits.
• MK-4 requires very high doses (15–45 mg/day) to be therapeutic, which makes it more of a pharmacologic intervention than a daily supplement.
• Look for third-party tested brands—Thorne, Life Extension, NOW Foods. Avoid proprietary blends that don’t disclose the actual MK-7 amount.
• Always pair with vitamin D3 if you’re supplementing for bone health, and get your levels checked periodically.

Disclaimer: This information is for educational purposes and doesn’t replace personalized medical advice. Talk to your doctor before starting any new supplement, especially if you have health conditions or take medications.