Vitamin K2 MK-4 vs MK-7: Why the Form and the Dose on the Label Are Both Doing Less Than You Think

Pick up a vitamin K2 product. Look at the Supplement Facts panel. Two numbers are doing all the work: the form — MK-4, MK-7, or sometimes "vitamin K2 complex" — and the dose in micrograms. Almost everything else on the label is marketing.

If you are taking K2 for bone metabolism, cardiovascular calcification protection, or as a co-factor with vitamin D3 supplementation, the form-and-dose combination on most retail bottles is not the form-and-dose combination the clinical literature actually used. The gap between the marketing dose and the research dose is structural, and it is the single most common reason a stack of D3 + K2 ends up doing less than the consumer thinks it is doing.

This is the framework I use to read a K2 label.

What vitamin K2 actually does

Vitamin K is a co-factor for a class of enzymes called gamma-glutamyl carboxylases. Those enzymes carboxylate specific glutamic acid residues on a small set of proteins, which is the modification that lets those proteins bind calcium. Without K, those proteins are made but never activated — they circulate in their inactive ("undercarboxylated") form and the calcium-dependent function they were built for never happens.

Two of those K-dependent proteins do most of the clinical work:

Osteocalcin is produced by osteoblasts and is responsible for binding calcium into the hydroxyapatite matrix of bone. Undercarboxylated osteocalcin is a measurable serum marker of K2 inadequacy and tracks with bone-turnover dysregulation. Clinical research on osteocalcin carboxylation status uses ucOC (undercarboxylated osteocalcin) as the readout.

Matrix Gla protein (MGP) is produced by smooth muscle cells in arterial walls and is the body's primary endogenous inhibitor of vascular calcification. Undercarboxylated MGP (dp-ucMGP, the dephosphorylated-undercarboxylated form) is the serum marker that tracks K2 status in the vascular compartment, and dp-ucMGP elevation is independently associated with cardiovascular calcification progression in multiple cohort studies.

The clinical case for K2 supplementation is about activating these two protein systems. The dose required to do that is the dose the bottle should be delivering. The dose on most retail bottles is not that dose.

MK-4 versus MK-7 — the two are not interchangeable

Vitamin K2 is not a single compound. It is a family of menaquinones, named MK-n where n is the number of isoprenoid units in the side chain. The two forms that matter for supplementation are MK-4 (short chain, 4 units) and MK-7 (long chain, 7 units).

They are not pharmacokinetically interchangeable. Treating them as the same thing — which most retail bundling does — is the source of most of the dosing confusion in the K2 category.

MK-4 has a short serum half-life — roughly 1 to 3 hours — and is the form the body uses most readily for the bone-targeted carboxylation work. The clinical research on MK-4 for bone health, including the Japanese trials in postmenopausal women, uses doses of 45 mg per day, split across three administrations of 15 mg each because of the short half-life. That dose — 45,000 micrograms per day — is the form-and-dose used in the trials that produced the bone-fracture-reduction signal Japan eventually approved as a pharmacological intervention.

MK-7 has a much longer serum half-life — roughly 3 days — and shows up in the bloodstream at measurable concentrations for far longer per oral dose. Long-half-life MK-7 is the form that delivers consistent enzyme activation across the full day from a single capsule. The clinical research on MK-7 for vascular and bone carboxylation outcomes uses doses of 180 to 360 micrograms per day (a few trials go up to 720 mcg), with 180 mcg being the most-studied minimum effective dose for shifting dp-ucMGP into the carboxylated range over 8 to 12 weeks.

The two doses are not in the same numerical universe. 45,000 mcg of MK-4 versus 180 mcg of MK-7. The shared label "vitamin K2" hides that the two products are doing different things at totally different dose magnitudes.

How most retail K2 products are dosed

Walk through the K2 shelf at any vitamin retailer and three patterns repeat:

The 100 mcg MK-7 capsule. The most common standalone K2 product. Roughly half the minimum clinically studied MK-7 dose. Delivers some carboxylation effect — MK-7 is potent and even sub-clinical doses move the needle somewhat — but is below the dose that drove the dp-ucMGP-reduction outcome in the trials. The marketing copy frames it as a "preventative" dose, which is a reasonable framing only if you grade "doing less than the studies did" as preventative.

The 45 mcg MK-7 bundled with D3. Often paired with 1,000 to 5,000 IU of D3 in a single softgel. The K2 dose here is a quarter of the clinical MK-7 minimum and is essentially a marketing inclusion rather than a functional dose. The D3 may be dosed correctly, but the K2 cofactor that the bundle is supposed to deliver is structurally below threshold.

The K2 "complex" with MK-4 + MK-7. Typically 1,000–1,500 mcg MK-4 plus 50–100 mcg MK-7. The MK-4 component is 1/30th to 1/45th of the clinical bone-fracture-trial dose. The MK-7 component is below the dp-ucMGP-reduction trial dose. Bundling two underdoses does not produce an effective dose. The label looks comprehensive. The math does not work.

The high-dose MK-7 (180–360 mcg) product. Less common, usually from a brand that explicitly cites the carboxylation literature. This is the form-and-dose that aligns with the published research and is the product the educated K2 buyer is actually looking for.

The dose distribution on the K2 shelf is not random. Most retail K2 underdoses for the same three reasons most supplement categories underdose: cost (high-dose MK-7 raw material runs 4–8x the cost of low-dose), regulatory risk (the higher-dose product invites a different scrutiny), and marketing breadth (a product at 100 mcg can be bundled into everything from a multivitamin to a calcium pill without the headline dose looking out of place).

Why "K2 complex" labels are doing the least

The K2-complex label is the worst-of-both-worlds product. The MK-4 fraction (typically 1,000–1,500 mcg) is at a dose that, given MK-4's 1–3 hour half-life and once-daily administration, delivers only intermittent carboxylase substrate and at a fraction of the trial dose. The MK-7 fraction (typically 45–100 mcg) is below the dp-ucMGP-reduction threshold.

The marketing logic is "more forms = better coverage." The pharmacology says: under-dose two forms and you under-deliver two effects. The K2 buyer reading the label sees comprehensiveness. The buyer reading the trial literature sees two truncated doses stacked in one capsule.

Two scenarios in which a complex would make sense: a research-grade product with 45 mg MK-4 + 180 mcg MK-7 (functionally never produced at retail because the cost would be prohibitive), or a clinical-monitored protocol with split-dose MK-4 across the day plus a single MK-7 administration (an order-and-administration pattern almost no retail consumer is set up to execute). Outside those scenarios, the K2-complex label is marketing dress on a dosing compromise.

Reading the label in 30 seconds

Front-of-bottle "Vitamin K2" tells you nothing. Flip to the back.

Step 1. Find the form. MK-4 only, MK-7 only, or a complex.

Step 2. Find the dose in micrograms (or milligrams in the rare correctly-dosed MK-4 product).

Step 3. Map dose against form:

• MK-7 alone: 180 mcg minimum effective dose per the carboxylation literature. 200–360 mcg is the cleanest functional range. Below 100 mcg is under-dosed.
• MK-4 alone: 45 mg (45,000 mcg) per day total, split TID, is the clinical-trial bone-outcome dose. No retail product at 100–1,500 mcg per day is in the same dose universe as the trial literature.
• K2 complex (MK-4 + MK-7): read both components against the form-specific thresholds. The vast majority of complexes are sub-threshold on both.

Step 4. Check the carrier oil. MK-7 is fat-soluble and absorbs meaningfully better with a meal containing fat, and a softgel with an MCT or olive oil carrier delivers better absorption than a dry capsule taken on an empty stomach. Most reputable MK-7 products are softgels in oil for this reason.

Step 5. Check the source. Synthetic MK-7 and natto-derived MK-7 are both used commercially. Natto-derived MK-7 is typically the trans-isomer (the bioactive form) at higher purity; some cheap synthetic MK-7 contains a mix of trans and cis isomers, and only the trans isomer is biologically active. A bottle that does not specify "all-trans MK-7" or "trans-MK-7 only" is worth questioning, especially at the cheaper end of the price range.

When K2 matters most

K2 supplementation has its strongest case in three populations:

Adults supplementing vitamin D3 at clinically meaningful doses (2,000+ IU/day) without K2. D3 supplementation increases calcium absorption from the gut. Without adequate K2 to activate MGP, more of that calcium ends up deposited in arterial walls rather than directed into bone. The published case for pairing D3 with K2 specifically is about traffic-directing the calcium D3 makes available. We covered the D3 dose math in detail in vitamin D3: why 1000 IU falls short; the K2 conversation here is the cofactor side of the same protocol.

Adults with documented bone-density concerns, especially postmenopausal women. This is the population the Japanese MK-4 trials studied. The 45 mg/day MK-4 dose used in those trials is essentially a pharmacological intervention rather than a typical supplement; a 180–360 mcg MK-7 daily dose is the consumer-supplement equivalent that targets the same carboxylation system through the long-half-life form.

Adults with cardiovascular calcification risk, especially those on calcium supplementation or with elevated coronary artery calcium scores. MK-7 at clinically dosed levels has shown dp-ucMGP reduction in the populations where vascular calcification is most relevant — the population most likely to benefit from getting MGP activated.

K2 in healthy young adults eating a varied omnivorous diet with green-vegetable intake and intermittent natto or aged cheese exposure is a lower-priority intervention. The clinical case strengthens with age, with D3 supplementation, with calcium supplementation, and with documented bone or vascular signals.

The bottom line

The K2 category is full of products that look like they are dosed for the published research and are not. The MK-7 product at 100 mcg per capsule is under the trial minimum by half. The MK-4 product at 100 mcg per capsule is under the trial dose by a factor of 450. The K2 complex with 1,000 mcg MK-4 plus 50 mcg MK-7 is under-dosed on both fractions and is marketing breadth dressed up as comprehensiveness.

The functional retail K2 product is MK-7 in the 180–360 mcg per day range, as all-trans MK-7, in an oil-carrier softgel, taken with a meal containing fat. The MK-4 form is real and the bone-fracture trial data is real, but the trial dose (45 mg/day split TID) is a pharmacological intervention nobody is selling at retail; consumer K2 supplementation, if it is going to do what the consumer is buying it for, is MK-7 at the dosed range that moves the carboxylation markers.

The lesson generalizes across the transparency thread we have been pulling on. The dose on the back of the bottle is the only thing that decides whether the supplement is doing what the label is selling. K2 is no different from creatine, magnesium, zinc, electrolyte sodium, or D3. Read the label. Match the dose to the research. If the math does not work, the product does not work.