Vitamin K2 MK-7 and D3: why they're paired

By The Krevie Team | Last reviewed: May 2026

Vitamin D3 increases the amount of calcium your intestine absorbs from food. Vitamin K2 — specifically the MK-7 form — activates two proteins, osteocalcin and matrix Gla protein, that direct that absorbed calcium into bone rather than into arterial walls and soft tissue. The two nutrients work on the same calcium pathway at different steps, which is why researchers and formulators routinely pair them. Krevie's The Foundation includes both: 2,000 IU of vitamin D3 and 100 mcg of vitamin K2 MK-7.

What vitamin K2 MK-7 is

Vitamin K exists in two main dietary forms: phylloquinone (K1), found in leafy vegetables, and menaquinones (K2), found primarily in fermented foods. Within the K2 family, menaquinones are classified by chain length — from MK-4 to MK-13. MK-7, or menaquinone-7, is the longest-chain form that occurs naturally in meaningful quantities in fermented soy foods such as natto.

The distinction between K1 and K2 is more than nomenclature. K1 is taken up almost entirely by the liver, where it is used in blood coagulation. K2, because of its longer side chain, distributes more widely into extrahepatic tissues — bone and the vasculature in particular — where it activates vitamin K-dependent proteins that K1 rarely reaches in sufficient quantity.

MK-7 specifically is valued for its pharmacokinetic profile. Unlike MK-4, which has a serum half-life of a few hours, MK-7 remains detectable in circulation for more than 24 hours after a single dose, producing stable, sustained activation of vitamin K-dependent proteins. This is why the majority of published RCTs on vitamin K2 and bone health use MK-7 rather than MK-4.

The two key proteins MK-7 activates are osteocalcin, which binds calcium into the bone matrix, and matrix Gla protein (MGP), which inhibits calcium deposition in soft tissue. Both require vitamin K-dependent carboxylation to become biologically active. Without sufficient K2, these proteins remain undercarboxylated — functionally inactive.

What the research shows

The evidence base for the K2–D3 combination has accumulated across observational cohort studies, mechanistic pharmacokinetic work, and randomised controlled trials.

Kuang et al. 2020 — meta-analysis of 8 RCTs

The most directly relevant evidence for supplementation comes from this meta-analysis published in Food & Function. Kuang et al. (2020) pooled eight randomised controlled trials involving 971 participants, examining the combined effect of vitamin K and vitamin D on bone mineral density (BMD) and markers of bone quality. The combination of vitamins K and D significantly increased total BMD (pooled effect size 0.316, 95% CI 0.031–0.601), and significantly decreased undercarboxylated osteocalcin (pooled effect size −0.945, 95% CI −1.113 to −0.778). Undercarboxylated osteocalcin is the inactive form — a lower level indicates that more osteocalcin has been activated by vitamin K2. The authors noted that a more favourable effect on BMD was expected when vitamin K2, rather than K1, was used.

Schurgers et al. 2007 — MK-7 pharmacokinetics and half-life

Schurgers et al. (2007), published in Blood, directly compared absorption and biological activity of synthetic vitamin K1 and natto-derived MK-7 in healthy volunteers. The primary finding was the substantially longer half-life of MK-7 versus K1: where K1 cleared overnight, MK-7 remained elevated in serum at 24 hours and accumulated to 7–8 times higher levels during prolonged intake. MK-7 also induced more complete carboxylation of osteocalcin than K1. The authors identified a clinical caution: preparations supplying 50 mcg per day or more of MK-7 may interact with oral anticoagulant treatment — important context for anyone on warfarin.

Geleijnse et al. 2004 — The Rotterdam Study

Before the mechanism was fully understood, population-level data pointed in the same direction. Geleijnse et al. (2004) examined vitamin K dietary intake in 4,807 Dutch participants from the Rotterdam Study cohort, followed for approximately seven years. Higher dietary menaquinone (K2) intake was associated with a reduced risk of coronary heart disease mortality (RR 0.43 for the upper tertile versus lower tertile, 95% CI 0.24–0.77) and with reduced severe aortic calcification (OR 0.48, 95% CI 0.32–0.71). Phylloquinone (K1) intake showed no such associations. The authors concluded this was consistent with menaquinone's role in activating matrix Gla protein in arterial tissue — the protein that inhibits arterial calcium deposition.

The matrix Gla protein mechanism

MGP is particularly relevant to the D3 pairing question. Vitamin D3 upregulates calcium absorption; in high-dose scenarios, the concern is whether absorbed calcium distributes appropriately. MGP, when fully carboxylated by vitamin K2, inhibits calcification of soft tissue and arterial walls. Inactive MGP (ucMGP) is measurable in blood and has been used as a marker of vitamin K2 status in research settings. Population studies consistently show that higher levels of ucMGP correlate with poorer vascular outcomes. The mechanistic pathway — D3 drives calcium in, K2 directs calcium to bone via osteocalcin and away from arteries via MGP — underpins the biological rationale for the combination.

How K2 MK-7 and D3 are used in Krevie

The Foundation provides 2,000 IU of cholecalciferol (vitamin D3, vegan source) and 100 mcg of vitamin K2 as MK-7 (menaquinone-7) per two-capsule daily serving.

The 100 mcg dose sits within the 90–180 mcg range used across published MK-7 RCTs, including the research summarised in the Kuang et al. 2020 meta-analysis. The 2,000 IU D3 dose aligns with the middle of the research-supported range — sufficient to meaningfully support calcium absorption, while remaining well within safe upper limits established by regulators.

Both nutrients are provided at doses that correspond to published research, not rounded estimates. This reflects Krevie's product philosophy: every dose on the label matches the dose used in trials, so there is a research basis for the quantity selected — not a marketing decision.

The Foundation also contains citicoline (CDP-choline) (500 mg), pine bark French maritime pine bark extract (200 mg), and saffron extract (28 mg) — providing a complete stack of ingredients each dosed to their primary published trials. See the full product page for the complete specification.

Frequently asked questions

Do I need to take K2 with D3?

Research suggests that pairing K2 with D3 makes biological sense. Vitamin D3 increases intestinal calcium absorption; vitamin K2 (particularly the MK-7 form) activates proteins that direct that calcium toward bone rather than soft tissue. The two nutrients operate on the same calcium homeostasis pathway but at different points within it. Supplements that provide both aim to support this coordinated mechanism.

What is the difference between MK-4 and MK-7?

Both are forms of vitamin K2 but differ in chain length and pharmacokinetics. MK-4 has a short half-life of several hours, meaning it clears the bloodstream quickly. MK-7 (menaquinone-7), derived from fermented foods such as natto, has a substantially longer half-life — circulating serum levels remain elevated 24 hours after intake. This extended presence allows more consistent activation of vitamin K-dependent proteins, which is why MK-7 is the form used in most published bone and cardiovascular research.

Why is 100 mcg the commonly researched dose of K2 MK-7?

Doses in the 90–180 mcg range appear consistently in published RCTs assessing MK-7's effect on osteocalcin carboxylation and bone mineral density. The meta-analysis by Kuang et al. (2020), which pooled eight RCTs, found significant BMD improvements when K2 was used alongside vitamin D. The 100 mcg dose used in The Foundation sits within this established research range.

Does taking high-dose vitamin D3 without K2 pose any risk?

This is a mechanistic concern discussed in the research literature, not a confirmed clinical outcome for most people. The concern is that high-dose D3 can increase calcium absorption substantially; without sufficient K2 to activate matrix Gla protein and osteocalcin, some of that calcium may accumulate in soft tissue. Research from the Rotterdam cohort (Geleijnse et al., 2004, n=4,807) found dietary menaquinone intake inversely associated with aortic calcification. For this reason, many formulators pair D3 with K2 MK-7.

Can K2 interfere with anticoagulant medication?

Yes — this is clinically important. Schurgers et al. (2007) found that preparations supplying 50 mcg per day or more of MK-7 may interfere with oral anticoagulant (warfarin) treatment in a clinically relevant way. Anyone taking blood-thinning medication should consult their GP before taking a vitamin K2 supplement.

References

Kuang X, Liu C, Guo X, Li K, Deng Q, Li D. The combination effect of vitamin K and vitamin D on human bone quality: a meta-analysis of randomized controlled trials. Food Funct. 2020;11(4):3280–3297. PubMed 32219282
Schurgers LJ, Teunissen KJF, Hamulyák K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279–3283. PubMed 17158229
Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100–3105. PubMed 15514282
Vermeer C. Vitamin K: the effect on health beyond coagulation — an overview. Food Nutr Res. 2012;56. doi:10.3402/fnr.v56i0.5329
McCabe KM, et al. Vitamin K2 — a neglected player in cardiovascular health: a narrative review. Open Heart. 2021;8(2):e001715. PMC8596038

Food supplement notice: The Foundation is a food supplement, not a medicine. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking any medications — including anticoagulants — or have a medical condition, consult your GP or healthcare professional before use. The information on this page is for educational purposes and does not constitute medical advice.