Vitamin K2
For informational purposes only — not medical advice. Always consult a qualified healthcare provider before making changes to your health regimen. Full disclaimer →
- K1 and K2 are different vitamins with different tissue targets — K2 is not just another form of K1. K1 activates clotting factors in the liver. K2 (particularly MK-7 and MK-4) activates proteins in bone (osteocalcin) and arterial walls (matrix Gla protein). They are absorbed differently, distributed to different tissues, and have meaningfully different functional effects. A diet high in K1 from leafy greens does not ensure adequate K2 for extrahepatic tissue needs — these are functionally distinct vitamins that require separate consideration.
- Matrix Gla protein (MGP) is the most potent known inhibitor of vascular calcification in the body — and it requires K2 to work. MGP is secreted by smooth muscle cells and chondrocytes in arterial walls. In its inactive (uncarboxylated) form, it cannot prevent calcium deposition in vessel walls. K2 activates MGP by carboxylating specific glutamate residues. Studies measuring ucMGP (inactive MGP) as a functional marker of K2 deficiency have found that high ucMGP independently predicts cardiovascular mortality — capturing functional K2 deficiency at the arterial level regardless of dietary intake measures. The Rotterdam Heart Study, a prospective cohort of 4,807 adults, found that the highest tertile of K2 intake was associated with 57% lower risk of aortic calcification and 52% lower cardiovascular mortality.
- Standard vitamin K blood tests measure K1, not K2 — making them uninformative for assessing cardiovascular and bone K2 status. If your lab reports a normal 'vitamin K' level, it is almost certainly measuring phylloquinone (K1). This tells you about dietary green vegetable intake and liver-dependent clotting factor activity — important information for anticoagulation monitoring — but provides no direct information about K2 availability for osteocalcin and MGP activation. The appropriate functional assessments are ucOC (available at some specialty labs) and ucMGP — or, as a practical surrogate, dietary K2 assessment and empirical supplementation.
- Vitamin D and K2 are synergistic and should be considered together. Vitamin D increases osteocalcin production — but osteocalcin requires K2 for activation. Supplementing vitamin D without adequate K2 may drive production of inactive osteocalcin that accumulates without directing calcium appropriately into bone. Several longevity practitioners recommend co-supplementation with K2 whenever vitamin D supplementation is used, particularly at doses above 2,000 IU/day. Conversely, adequate K2 ensures that calcium mobilized by vitamin D signaling reaches its intended destination in bone rather than being deposited in soft tissues.
- K2 supplementation does not meaningfully interact with warfarin — K1 is the primary anticoagulant concern. Warfarin blocks Vitamin K-dependent clotting factor activation, and K1 dietary intake is the primary variable affecting warfarin dosing stability. K2 (particularly MK-7 at supplemental doses of 100–200 mcg/day) also has some clotting factor-activating activity and should be used cautiously in people on warfarin without anticoagulation monitoring. However, the clinical impact of standard supplemental MK-7 doses on warfarin INR is much smaller than the impact of variable K1 dietary intake. For people not on anticoagulants, K2 supplementation has an excellent safety profile with no known toxicity.
Why Western Diets Are Functionally K2 Deficient
Vitamin K research has historically focused on K1, because K1 deficiency produces measurable changes in blood clotting — a serious and visible clinical problem. K2 deficiency, by contrast, produces changes in bone and vascular tissue that accumulate silently over decades and only become apparent as osteoporosis and cardiovascular disease in midlife and beyond.
This time horizon has made K2 deficiency easy to overlook. K1 deficiency shows up as a bleeding tendency within days of dietary deprivation. K2 insufficiency shows up as arterial calcification and reduced bone density over years to decades — precisely the timescale that makes it relevant to longevity but difficult to study in clinical trials.
Western dietary patterns are particularly low in K2 for several reasons: fermented foods (the richest K2 source, particularly natto) are not widely consumed; the shift toward low-fat dairy removed MK-4-containing fat-soluble vitamins from dairy products; reduced consumption of organ meats and egg yolks reduced MK-4 intake; and the use of antibiotics reduces gut bacterial K2 production. The practical result is that most adults in Western countries have functional K2 insufficiency at the extrahepatic tissue level — adequate K1-dependent clotting function, but inadequate K2 for optimal osteocalcin and MGP activation.
The Calcium Traffic Director: Bone vs. Arteries
The most compelling case for K2 in longevity medicine comes from the Rotterdam Heart Study — a prospective cohort study of 4,807 Dutch adults followed for 7–10 years. Participants with the highest tertile of dietary K2 intake had a 57% lower risk of aortic calcification and a 52% lower risk of cardiovascular mortality compared to those in the lowest tertile. Critically, the association was specific to K2: K1 intake showed no significant association with either aortic calcification or cardiovascular mortality. 1
This specificity — K2 protective, K1 neutral for cardiovascular outcomes — aligns precisely with the biological mechanism: K2-dependent MGP in arterial walls prevents vascular calcification; K1 does not activate MGP effectively at physiological dietary concentrations.
The simultaneous bone benefit of K2 creates a particularly compelling longevity profile: reducing arterial calcification (one of the primary drivers of cardiovascular mortality) while improving bone mineralization (reducing fracture risk) through the same calcium-directing mechanism.
| Marker | What It Measures | Optimal | Availability |
|---|---|---|---|
| Serum K1 (standard test) | Dietary K1 intake; clotting factor activity | Normal range | Consumer labs (Ulta) |
| Serum MK-7 | Circulating K2 (MK-7) directly | Specialty reference | Specialty labs only |
| ucOC (uncarboxylated osteocalcin) | Functional K2 status in bone | < 4.5 µg/L | Some specialty labs |
| ucMGP (uncarboxylated MGP) | Functional K2 status in arteries | As low as possible | Research / specialty labs |
| Range Type | Value (ng/mL (serum K1); µg/L (ucOC)) | Notes |
|---|---|---|
| Standard Clinical Range | Serum MK-7: varies by lab and assay (no established population reference range) · Functional marker (ucOC): < 4.5 µg/L suggests adequate K2 status · Standard 'Vitamin K' test measures K1, not K2 specifically | Designed to identify disease risk — not longevity optimisation. |
| Longevity-Optimal Target | Functional: ucOC < 4.5 µg/L · ucMGP as low as possible (specialty assay) |
Associated with reduced all-cause mortality and extended healthspan.
Testing vitamin K2 status is genuinely challenging. Most consumer labs, including Ulta Lab Tests, measure total vitamin K (predominantly K1/phylloquinone), which reflects dietary green vegetable intake but does not reflect K2 status. Dedicated serum MK-7 assays require specialty labs. The most clinically useful approach for assessing functional K2 status is measuring uncarboxylated osteocalcin (ucOC) — the inactive form of osteocalcin that accumulates when K2 is insufficient to activate it. A simpler practical approach used in longevity medicine is empirical supplementation with MK-7 (100–200 mcg/day) given the strong safety profile, low dietary K2 intake in most Western diets, and mechanistic rationale. Serum K1 measurement is useful for assessing K1-dependent clotting factor status and warfarin monitoring but does not inform K2-dependent bone and vascular protein activity.
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What foods are highest in vitamin K2?
The highest K2 source by a substantial margin is natto — a Japanese fermented soybean product — which contains 800–1,000 mcg of MK-7 per 100g serving. A single serving of natto provides far more K2 than any other food source. Hard cheeses (gouda, brie) contain meaningful amounts of MK-8 and MK-9. Egg yolks contain MK-4. Butter, liver, and full-fat dairy from grass-fed animals contain modest MK-4. The low K2 content of typical Western diets is primarily because fermented foods (the richest K2 sources) are not widely consumed, and because the transition to low-fat dairy and reduced organ meat consumption removed two meaningful K2 contributors. Most adults eating a typical Western diet consume 10–40 mcg of K2 per day — well below the 100–200 mcg range studied in supplementation trials.
What is the difference between MK-4 and MK-7 supplements?
MK-4 and MK-7 are both forms of K2 but differ in side-chain length, bioavailability, and pharmacokinetics. MK-4 has a short side chain and a short half-life (hours), requiring multiple daily doses to maintain blood levels. Most studies using MK-4 for bone outcomes used pharmacological doses (15 mg three times daily — 45 mg/day), which are 100× higher than MK-7 doses used for comparable effects. MK-7 has a long side chain and much longer half-life (72 hours), allowing once-daily dosing at 100–200 mcg to maintain steady serum levels and vascular tissue distribution. MK-7 more effectively raises serum K2 levels and is better distributed to extrahepatic tissues (arterial walls, bone) compared to MK-4 at similar doses. For longevity supplementation, MK-7 at 100–200 mcg/day is the most practical approach and has the best evidence base for vascular and bone endpoints at physiological supplemental doses.
Should I supplement K2 if I'm already taking vitamin D?
This is one of the more consistently supported nutritional co-supplementation recommendations in longevity medicine. Vitamin D increases production of osteocalcin and may mobilize calcium from gut absorption — but both of these effects require K2 for appropriate downstream direction of calcium into bone and away from soft tissues. Multiple observational studies suggest that the combination of adequate vitamin D and K2 produces better bone density outcomes than vitamin D alone. The theoretical concern about vitamin D supplementation without K2 — that increased calcium absorption may contribute to vascular calcification if K2-dependent MGP activation is inadequate — is not yet conclusively proven in RCT data, but has a plausible mechanistic basis. Given K2's excellent safety profile, the combination is a low-risk, potentially significant synergy for anyone supplementing vitamin D at meaningful doses.
How does K2 affect cancer risk?
There is emerging but not yet conclusive evidence suggesting K2 may have anti-cancer properties, particularly for liver and prostate cancer, through activation of steroid and xenobiotic receptor (SXR) signaling and induction of apoptosis in cancer cell lines. The CRIB (Cancer Reduction in Bone) trial found that high-dose MK-4 reduced non-hepatic cancer incidence in a Japanese cohort, though this has not been consistently replicated. Observational data from the EPIC-Heidelberg cohort found that higher K2 intake was associated with lower prostate cancer risk. While these findings are promising, the evidence is preliminary compared to K2's bone and cardiovascular data. Cancer risk reduction is not currently a primary indication for K2 supplementation, but it adds to the overall favorable risk-benefit profile for supplementation in longevity contexts.