Vitamin K

QUICK REF

• Evidence: Coagulation 5/5 (essential) · MK-4 45mg osteoporosis (Japan) 4/5 · MK-7 180-360mcg bone 4/5 · Vascular calcification slowing 3/5 · CHD mortality 2/5 (observational) · Cognition/diabetes/cancer 2/5 or less
• Dose: General adequacy 90-120 mcg/d phylloquinone (K1) from food. Supplementation: MK-7 100-180 mcg/d once daily with fat. MK-4 5-15 mg/d if stacked; 45 mg/d only as Japanese prescription (Glakay) for osteoporosis.
• Timing: Largest fat-containing meal. MK-7 once daily (t½ 72h); MK-4 split 2-3×/d (t½ 1-2h).
• Lab/Monitor: PT/INR (normal 11-13.5 s / 0.8-1.2). Functional K status: undercarboxylated osteocalcin (ucOC, <20% optimal), dp-ucMGP (emerging vascular + heart-failure biomarker, PMID 41603031), PIVKA-II (<2 ng/mL).
• Key interactions: Warfarin/VKA (clinical — requires consistent intake, MD supervision). IV push K1 (rare anaphylactoid, slow infusion mitigates). Broad-spectrum antibiotics >2-3 weeks (modest depletion).
• STATUS (2026-04-17): ADD for newborn K1 IM prophylaxis (universal standard). CONDITIONAL for MK-7 100-180 mcg/d (adds most value if high-dose D3, postmenopausal, CKD, or malabsorption). WATCH for 2026 large-N hard-endpoint RCTs. Health utility 7/10 compound-intrinsic.

Clinical Summary

Vitamin K is an obligate cofactor for γ-glutamyl carboxylase (GGCX), which adds γ-carboxyl groups to glutamate residues in vitamin K-dependent proteins (VKDPs): clotting factors II/VII/IX/X and protein C/S/Z (hepatic), osteocalcin and matrix-Gla-protein (MGP) (extrahepatic), plus Gas6, Gla-rich protein, and periostin. Activated VKDPs bind calcium; without them, blood fails to clot, arteries calcify more readily, and bone mineralization is impaired. Vitamin K is recycled through the vitamin K cycle; VKORC1 (the enzyme warfarin inhibits) regenerates the active hydroquinone form.

Two human-relevant vitamers differ in pharmacokinetics and tissue distribution:

• Phylloquinone (K1): plant-derived, short t½ (1-2 h), hepatically concentrated, drives coagulation.
• Menaquinones (K2, MK-4 through MK-13): bacterial/fermentation-derived; MK-4 synthesized in tissues from K1 via a geranylgeranyl side-chain swap; MK-7 has the longest serum t½ (~72 h) and preferentially accumulates in bone, arterial wall, and brain.

Evidence anchors by domain:

• Coagulation & neonatal VKDB: universal IM phytonadione prophylaxis is a direct-cause, 5/5 intervention — refusal rates are rising (US 2.92% → 5.18% from 2017-2024; PMID 41359326) and documented ICH cases (PMID 41514043) are a sentinel event of the misinformation era (PMID 41916583).
• Osteoporosis: pharmacological MK-4 45 mg/d reduces fractures in Japanese postmenopausal cohorts (Cockayne 2006 MA, 7 RCTs; PMID 16801507) but failed to replicate in North American women (Binkley 2009, PMID 19113922). Physiological MK-7 180-360 mcg/d preserves bone strength and vertebral height over 3 years (Knapen 2013, PMID 23525894); 2024-2026 meta-analyses (PMIDs 39657786, 41268154, 41393956) continue to show modest BMD/ucOC benefits.
• Vascular calcification: a surrogate-endpoint story. MK-7 and K1 slow CAC progression by 6-12% over 2-3 years (Shea 2009, PMID 19386744; de Vries 2025, PMID 40077685) but do not reverse established calcification. The AVADEC K2+D3 RCT (Diederichsen 2022, PMID 35465686) is the largest hard-endpoint trial on aortic valve calcification; its 2025 substudy on epicardial fat (PMID 41100911) keeps the signal alive. dp-ucMGP now extends beyond vessels to heart failure prognosis (PMID 41603031).
• Ferroptosis axis (2024-2026 emergent mechanism): K and K-cycle enzymes protect osteoblasts (PMID 41458254), vascular smooth muscle (PMID 40992546), neurons (PMIDs 41296108, 41609979), hepatocytes (PMID 41055715), RPE (PMID 40108164), and chondrocytes (PMID 40496065) from iron-dependent lipid peroxidation. Mechanism is preclinical but unifies previously unrelated findings.

The headline population where K2 has a Hell-Yes profile is postmenopausal women on high-dose D3/calcium stacks with elevated ucOC or CAC ≥100 — the compound is cheap, safe, and the physiological case is plausible. For healthy vegetable-eaters there is no evidence of meaningful additional benefit beyond dietary adequacy.

Indications & Evidence

Legend:

• Type: DC Direct Cause · PC Probable Cause · BC Biomarker Correlation (surrogate only) · UCC Uncontrolled Confounder Correlation · OA Observed Association · AHE Adjunctive Hypothesis Explorer · ME Mechanistic Evidence · NE No/Null Evidence · FA Failed Attempt
• BH = Bradford Hill criteria met /9 (strength, consistency, specificity, temporality, dose-response, plausibility, coherence, experiment, analogy)
• Safety: -- no isolated FAERS signal · MON monitor · WARN serious signal · AVOID contraindicated
• Star ceilings per type: DC ≤5/5 · PC ≤4/5 · BC ≤3/5 · UCC ≤2/5 · OA ≤2/5 · AHE ≤2/5 · ME ≤2/5 · NE ≤1/5 · FA ≤1/5

Prescribing

Forms

Dose by indication

Absorption & timing

• Fat is required — 10-15 g fat in the co-meal increases absorption 4-6× (the single biggest lever).
• MK-7 t½ (~72 h) permits once-daily dosing without trough issues. K1 and MK-4 need 2-3×/d to maintain extrahepatic levels.
• Light- and oxidation-sensitive; opaque bottles, <25 °C, refrigeration not required.
• Isomer purity matters — independent lab surveys have found ~2/3 of US MK-7 products fail ≥98% all-trans specification. Prefer MenaQ7 branded or other products with COA showing trans-isomer >98% (PMC 9790681; Nutraceutical Business Review).

Condition-Specific Protocols

Postmenopausal osteoporosis (Western population)

• Goal: reduce bone loss rate, lower ucOC, preserve vertebral height.
• Stack: MK-7 180 mcg/d + D3 1,000-2,000 IU + elemental calcium 1,000-1,200 mg (from diet preferred) + magnesium 300-400 mg + weight-bearing exercise.
• Monitoring: DEXA every 24 months; ucOC annually if accessible; 25(OH)D 30-50 ng/mL; serum calcium normal.
• Duration: minimum 3 years before expecting BMD signal; continuous thereafter.
• Realistic expectation: fracture reduction not demonstrated at this dose in Western populations — the benefit is slower bone loss + ucOC normalization, not MK-4 45 mg-scale fracture prevention.

Osteoporosis with documented high ucOC + access to MK-4 45 mg (rare outside Japan)

• Goal: fracture risk reduction per Cockayne 2006 meta-analysis.
• Regimen: MK-4 15 mg PO three times daily with fat-containing meals.
• Monitoring: PT/INR baseline and at 1 month (to exclude occult VKA); ucOC q6mo; DEXA q24mo.
• Caveats: evidence base is Japanese-specific; Binkley 2009 (PMID 19113922) was null in North American women over 12 months. Genetic or dietary factors not fully characterized.

High-CAC subject on high-dose D3

• Goal: slow CAC progression (reversal not established — Kahn MD essay).
• Regimen: MK-7 180-360 mcg/d + D3 at dose needed to keep 25(OH)D 40-60 ng/mL + magnesium glycinate 300-400 mg/d + stop any calcium supplement above dietary unless documented deficiency.
• Monitoring: CAC scan every 2-3 years; dp-ucMGP if available.
• Realistic expectation: ~6-12% slower progression over 2-3 years in adherent subjects.

CKD 3b-5 / dialysis

• Goal: counter the near-universal functional K2 deficiency in uremia; attenuate vascular calcification.
• Regimen: MK-7 360 mcg/d (or 360 mcg 3×/wk post-dialysis per Westenfeld protocol); avoid calcium-based phosphate binders where possible.
• Caveat: many CKD patients on VKA for AF — any K2 supplementation requires nephrology + cardiology supervision.
• Evidence: Westenfeld 2012 (PMID 22169620), Naiyarakseree 2023 (PMID 37299386), Lima 2026 (PMID 41052658).

Cystic fibrosis / fat malabsorption

• Goal: normalize PT/INR and ucOC despite defective fat-soluble vitamin absorption.
• Regimen: K1 1-10 mg/d oral water-miscible with PERT + fat; parenteral K if oral insufficient. Follow PT q3-6mo; ucOC annually; DEXA q2-5y.
• Evidence: Cochrane 2020 (PMID 32497260).

Safety

Overall profile

Vitamin K is among the safest fat-soluble vitamins. No tolerable upper limit has been set by IOM or EFSA because no toxicity has been reproduced at any oral dose studied. MK-4 45 mg/d (375× the adequate intake) has been given to postmenopausal women for 2-3 years without dose-limiting toxicity. Menadione (K3) is a separate compound — banned for human OTC use since the 1960s due to hemolytic anemia and hyperbilirubinemia in infants; still permitted as an animal-feed additive.

Adverse effects

FAERS Signal Table (2026-04-17 BioMCP pull)

Interpretation per feedback_faers_supplement_noise: the K1 phytonadione numbers reflect the hospital-inpatient denominator, not oral supplementation risk. The only compound-specific signal is IV-push anaphylactoid reaction, which is well known and fully mitigated by slow infusion. Oral K1 and K2 have no distinctive FAERS signature.

Contraindications

• Absolute: active VKA (warfarin, phenprocoumon, acenocoumarol) therapy WITHOUT physician supervision. Variable K intake causes INR swings; high-dose MK-4 (≥20 mg) can fully reverse anticoagulation. Consistent 90-120 mcg/d can actually stabilize INR but only under MD direction.
• Relative: antiphospholipid syndrome or prior unprovoked VTE not on anticoagulation — theoretical concern only; no evidence of harm at physiological doses.
• Menadione (K3): contraindicated for human use; do not use supplements that list K3.

Drug interactions

Special populations

• Pregnancy: AI 90 mcg/d; no teratogenicity at supplemental doses; vitamin K antagonists (warfarin) are contraindicated — teratogenic.
• Lactation: AI 90 mcg/d; breast milk K is low (1-2 mcg/L) — does NOT replace neonatal IM prophylaxis. Masuda 2026 (PMID 41076804) shows prepregnancy obesity independently raises neonatal K deficiency risk.
• Neonates: IM K1 0.5-1 mg (0.3-0.5 mg/kg for <1,500 g) within 6 hours of birth. Oral regimen is second-line — Swiss data (PMID 41545738) confirms modern oral protocols work but are more failure-prone. US refusal climbed from 2.92% to 5.18% (2017-2024; PMID 41359326); Jacobs 2026 frames VKDB-after-refusal as a sentinel event (PMID 41916583); Vazquez 2026 reports large ICH in a refusal case (PMID 41514043). Delayed complementary feeding (PMID 41359880) and late-onset VKDB presenting as hematuria (PMID 41733089) remain clinical tripwires.
• Infants 0-12 mo: AI 2.0-2.5 mcg/d; formula is sufficient; breastfed at risk without prophylaxis.
• Children 1-18 y: AI 30-75 mcg/d; supplementation only for malabsorption, chronic antibiotics, or very low vegetable intake.
• Renal impairment (dialysis): deficiency prevalence 70-90%; investigational 360-1,080 mcg/d MK-7; clearance not a concern (hepatic metabolism).
• Hepatic impairment (Child-Pugh C): K may not fully correct PT if synthetic function is exhausted; trial parenteral K is reasonable but absence of response signals end-stage failure rather than K deficiency.

Synergies & Stacking

Individual Response Modifiers

Sex-Specific Considerations

Genetic Modifiers

Pharmacogenomic datasets continue to grow (Al Hamad 2025 PMID 41155858; Sridharan 2026 PMID 41892871), but no consumer genotyping panel currently gives K-dose-actionable output outside warfarin initiation.

Community & Anecdotal Evidence

DISCLAIMER: The content in this section is anecdotal and community-sourced. It is NOT clinical evidence. Reported subjective effects are unreliable, often contradictory, and may reflect placebo, nocebo, or selection bias. Doses cited here are what users reported taking, not what evidence supports. Safety claims in this section cannot substitute for the Safety section above.

Source Communities Surveyed

Reddit (r/Nootropics, r/Supplements, r/Biohackers, r/VitaminD, r/Osteoporosis, r/longevity), Longecity, Inspire bone-health forums, LowToxinForum, HairLossTalk/Looksmax, Phoenix Rising, Bryan Johnson Blueprint, Chris Masterjohn PhD, Rhonda Patrick, Peter Attia, Mercola (flagged), Dr. Berg (flagged), Dennis Goodman MD, Kate Rheaume-Bleue (Calcium Paradox), Weston A. Price Foundation, Japanese Glakay / natto communities.

Reported subjective effects (frequency approximate)

Common community dosing (NOT evidence-based recommendations)

Red Flags & Skepticism Notes

• "Big Pharma hides K2" (Mercola ecosystem, some UK supplement sellers, Calcium Paradox marketing) — boilerplate conspiracy that sells product; dismiss.
• Calcium Paradox (Rheaume-Bleue) — book popularized the "K2 redirects calcium" thesis; evidence base is mechanistic + Rotterdam observational, not RCT. Cardiologists dispute reversal claims.
• Weston Price "Activator X" / dental remineralization — Price's 1930s observational ethnography was real; modern claims that K2 reverses cavities are extrapolation without clinical support.
• Eric Berg DC — chiropractor, not MD; aggressive 10,000 IU D3 + "mandatory" K2 marketing; treat as commercial content, not clinical guidance.
• Mercola commercial bundling — product quality OK per iHerb reviews; rhetoric inflated; frequent conspiracy framing.
• Bryan Johnson maximalist dose (600 mcg MK-7 + 5 mg MK-4 + 1.5 mg K1) — transparent protocol but 6× Rhonda Patrick's dose with no marginal-benefit evidence.
• Isomer purity is a LEGITIMATE quality concern, not conspiracy — ~2/3 of US MK-7 products have failed all-trans ≥98% specification in independent testing. Prefer MenaQ7 branded or products with COA.

Folk vs Clinical Reality Check

Deep Dive

Mechanism (2024-2026 expansion)

The classical mechanism is γ-glutamyl carboxylase (GGCX) adding a CO₂-derived carboxyl group to glutamate residues in VKDPs, using reduced vitamin K hydroquinone as the obligate cofactor. The oxidized epoxide product is recycled by VKORC1 (the warfarin target). Zhang 2026 (PMID 41888148) and Wu 2025 (PMID 41290650) provided the first atomic-resolution structures of human GGCX, revealing the bicarbonate-mediated carboxylation/epoxidation mechanism. These structures enable rational design of next-generation anticoagulants (PMID 41428972, small-molecule GGCX inhibitor).

Ferroptosis axis: 2024-2026 work repositioned vitamin K as an anti-ferroptotic agent across tissues. FSP1 (AIFM2) reduces vitamin K to its hydroquinone form, which scavenges lipid peroxyl radicals and suppresses iron-dependent cell death. Documented across:

• Osteoblast — NRF2/FSP1 inhibits glucocorticoid-induced ferroptosis (PMID 41458254)
• Aortic smooth muscle — MK-4 ameliorates abdominal aortic aneurysm via NRF2/GCLM (PMID 40992546)
• Neurons — VKORC1L1 loss → K-cycle disorder → neuronal ferroptosis in spinal cord injury (PMID 41609979); K1 protects against OGD injury via xCT/GPX4 (PMID 41296108)
• Hepatocytes — K1 attenuates APAP ferroptotic damage via Keap1/Nrf2/HO-1 (PMID 41055715)
• Retinal pigment epithelium — K and its antagonist in ferroptosis-damaged RPE / choroidal neovascularization (PMID 40108164)
• Chondrocytes — K as anti-ferroptotic drug in OA via Gas6 (FDA drug screen, PMID 40496065)
• AD mouse model — K-Trolox hybrid anti-ferroptotic/oxytotic (PMID 40839917)

This unifies previously unrelated observations but remains preclinical — no human RCT has yet tested K as a ferroptosis-targeted therapy.

MGP / dp-ucMGP: matrix-Gla-protein is the primary extrahepatic K-dependent inhibitor of vascular calcification. Vidula 2026 (PMID 41603031) extends dp-ucMGP as a prognostic biomarker in heart failure; Viegas 2026 (PMID 41861711) engineered γ-carboxylated Gla-rich protein EVs that modulate both inflammation and vascular calcification.

Osteoporosis literature — the East-West split

Cockayne 2006 (PMID 16801507) pooled 7 RCTs showing MK-4 45 mg/d reduces hip fracture RR 0.23, vertebral 0.40. All 7 RCTs were Japanese. Binkley 2009 (PMID 19113922) ran the largest Western replication — 381 North American postmenopausal women on K1 1 mg/d or MK-4 45 mg/d for 12 months, all received Ca + D — both K arms reduced ucOC but produced NO BMD improvement vs placebo. Possible reasons: shorter duration, different genetic background (VKORC1, CYP4F2 allele frequencies differ by ancestry per PMID 41155858), higher baseline calcium intake diluting signal, different bone-remodeling set point.

2024-2026 meta-analyses (Xie 2024 PMID 39657786; Zhang 2025 PMID 41268154; Wen 2025 PMID 41393956) continue to show a modest, heterogeneous BMD signal in K2-supplemented groups. The honest reading: MK-4 45 mg is a Japanese prescription treatment, not a generalizable supplement dose; MK-7 180 mcg/d is a reasonable bone-loss-slowing tool with 3-yr evidence; neither is a standalone fracture-prevention strategy outside Japan.

Vascular calcification — surrogate endpoint trap

Rotterdam Study (Geleijnse 2004 PMID 15514282) is the observational foundation — 4,807 adults, menaquinone intake >32.7 mcg/d associated with 57% lower CHD mortality. Phylloquinone intake showed no association. Critically, this is observational data susceptible to confounding (people eating more fermented food differ systemically from those who don't).

Shea 2009 (PMID 19386744, 388 adults, K1 500 mcg/d for 3 yrs) showed 6% slower CAC progression in per-protocol analysis. Beulens 2009 (PMID 18722618, N=564 cross-sectional) showed inverse association. None of these are hard-endpoint RCTs.

Diederichsen 2022 (PMID 35465686, AVADEC, Circulation) randomized men 65-74 with aortic valve calcification to MK-7 720 mcg + D3 25 mcg/d vs placebo for 2 years — failed primary endpoint of AVC progression. The 2025 AVADEC substudy (PMID 41100911) showed K2+D3 effects on epicardial adipose tissue and systemic inflammation. de Vries 2025 (PMID 40077685) ran 1 yr MK-7 180 mcg/d in postmenopausal women — modest PWV + BP effects, not uniform.

The honest synthesis: vitamin K2 probably slows vascular calcification progression modestly in adherent subjects with existing calcification. It does not reverse established calcification (Kahn MD). It has NOT demonstrated hard-endpoint CVD reduction in RCT. The evidence fits surrogate-endpoint risk per feedback_surrogate_endpoint_pattern.

Clinical Trials (selected 2024-2026)

Guidelines (2020-2026)

Guideline gap: despite three K2 meta-analyses (Ma 2022, Zhou 2022, Su 2019), no Western medical society endorses K2 supplementation for osteoporosis or cardiovascular prevention in healthy adults. Japan remains the only country with prescription K2 (MK-4 45 mg Glakay) for osteoporosis.

Ataraxia Verdict (as of 2026-04-17)

Hype Check

Vitamin K has accumulated an outsized folk mythology around K2. The most consistent hype pattern is the "K2 redirects calcium" framing (Calcium Paradox, Mercola, Berg) which overstates what is in fact a modest surrogate-endpoint slowing of vascular calcification into a civilization-level missing-nutrient narrative. The second hype pattern is MK-4 "Activator X" dental remineralization, which rests on 1930s observational ethnography without modern clinical replication. Bryan Johnson's 600 mcg/d MK-7 is a maximalist outlier without marginal-benefit evidence. The third hype pattern is "K2 mandatory with any D3 dose" — plausible at high-dose D3 on mechanistic grounds, but no RCT establishes the ratio. The JAMA 2024 nocturnal-leg-cramps RCT was retracted (PMID 39466236 → 40314950) after being widely cited.

Evidence Classification

Star ceilings enforced per causal-taxonomy table; no indication rated above its type allows.

Evidence Gaps

• No hard-endpoint CVD mortality RCT for K2 supplementation. All mortality data is observational.
• MK-4 45 mg Western replication remains only Binkley 2009 (N=381, 12 mo, null). Longer and larger Western RCTs at the 45 mg dose do not exist.
• No RCT establishes any specific D3:K2 ratio.
• No head-to-head RCT comparing MK-4 vs MK-7 on the same hard endpoint.
• CKD/dialysis optimal K2 dose + form is still being established; VitaVasK-class trials ongoing.
• No RCT for K2 in cognitive outcomes, despite strong mechanistic rationale.
• Pediatric K supplementation beyond neonatal prophylaxis is extrapolated, not trialed.
• Pharmacogenomic K dosing (VKORC1, CYP4F2, GGCX) is validated for warfarin but not for supplementation.
• Sex-stratified evidence base for men is thin — most RCTs enrolled postmenopausal women.

Bias Flags

• Japanese MK-4 dominance — virtually all pharmacological-dose fracture evidence comes from one population, and Eisai (Glakay manufacturer) is linked to much of the dissemination ecosystem.
• NattoPharma/Kappa Bioscience / Gnosis by Lesaffre hold most MK-7 patents and sponsor a large share of MK-7 RCTs (MenaQ7 is a branded ingredient). Trial heterogeneity and publication bias plausible.
• Rotterdam Study is 20+ years old; dietary menaquinone estimation from food-frequency questionnaires is noisy and confounded by broader dietary quality.
• Observational-to-causal leap: Rotterdam → "K2 saves your heart" is exactly the surrogate-endpoint pattern flagged elsewhere in this vault.
• Community over-weighting of MK-7 PK advantage — pharmacokinetic superiority does not automatically translate to clinical superiority on hard endpoints.

Manipulation Flags

• Industry marketing: "Proprietary blend" D3+K2 products obscure doses; "clinical strength" claims without ingredient-level evidence. Isomer purity failures in ~2/3 of US MK-7 products (independent testing) mean some products are underdosed; use COA-backed brands.
• Influencer economics: Mercola and Dr. Berg derive direct commercial benefit from D3+K2 bundle sales; content is marketing, not clinical guidance. Masterjohn, Rhonda Patrick, and Attia operate with paid content but are more evidence-bounded. Bryan Johnson is transparent but runs an N=1 protocol with commercial extension.
• Cui bono pro-supplementation: NattoPharma + branded MK-7 ecosystem + preventive-cardiology practices + supplement retailers. Legitimate researchers also benefit from funding linked to K narratives.
• Cui bono anti-supplementation: Pharma bone-drug competitors (bisphosphonates, denosumab, romosozumab) have incentive to minimize K2; pharma warfarin-era incentive was to restrict K intake variability. Neither has manifest as active fearmongering in the current literature.
• Supply chain vs compound: isomer purity issue is a supply-chain concern, not an indictment of K2 itself.
• Red team (10 angles):
  1. Logical consistency — internally consistent with calcium-trafficking mechanism
  2. Evidence quality — strong for coagulation, moderate for bone, biomarker-only for vascular
  3. Cui bono — dual-sided, balanced
  4. Time horizon — decades of use; long-term safety is unusually strong
  5. Steelman against — "all K2 benefit is explained by confounded healthy-user effect + surrogate endpoints" is not fully refutable today
  6. Reversibility — stops cleanly (except MK-7 t½ delay)
  7. Second-order — supplement-driven over-emphasis may crowd out dietary improvement
  8. Historical precedent — Japanese MK-4 has 30-yr prescription-use track record
  9. Emotional loading — Calcium Paradox narrative is emotionally loaded ("hidden missing nutrient")
  10. Stranger test — would a random person with no supplement-industry exposure still conclude "take K2"? For newborns, yes. For general adults, weakly. For postmenopausal women with high ucOC, yes.

Decision Support

Health utility: 7/10 compound-intrinsic. The 7 reflects: (1) essential nutrient with universal clinical value in newborns, (2) clear benefit in specific high-value populations (postmenopausal women with bone loss, CKD, malabsorption), (3) modest but real surrogate-endpoint effects on vascular calcification, (4) very wide safety margin, (5) low cost. The score is not higher because most adults get adequate K from diet, the vascular mortality story is observational, and the dental / cognitive / cancer / testosterone claims are folk-level.

Opportunity cost: Low. $5-40/month; trivial complexity; stacks cleanly with D3/Mg/Ca; one real drug interaction (VKA). The main cost is attention — K2 mythology eats mindshare that might be better spent on sleep, exercise, and dietary improvement.

Verdict: CONDITIONAL. ADD for newborn K1 IM (absolute). ADD for MK-7 100-180 mcg/d IF on high-dose D3, postmenopausal with bone-loss markers, CKD, or documented malabsorption. WATCH LIST for healthy adult with adequate green-vegetable intake — dietary K1 plus fermented-food MK occasional is reasonable. SKIP menadione (K3). SKIP CAC-reversal claims.

Bottom Line

Vitamin K is an essential, cheap, safe nutrient whose K1 form is the universal neonatal standard of care and whose K2 menaquinones have modest-but-real effects on bone preservation and vascular-calcification slowing in specific populations. The folk mythology (Calcium Paradox, Activator X, mandatory D3:K2 ratios, CAC reversal) overstates the clinical reality, which is better described as "slows progression of surrogate endpoints at physiological doses; fracture benefit is pharmacological-dose + Japanese-population-specific." Worth taking if on high-dose D3 or in a bone/vascular-risk population; probably not worth optimizing over if you eat leafy greens daily and are otherwise healthy.

Practical Notes

Brands & Quality

• MenaQ7 (NattoPharma/Gnosis by Lesaffre) — most-studied branded MK-7; all-trans, COA available.
• Life Extension Super K — K1 1 mg + MK-4 1 mg + MK-7 100 mcg combination, third-party tested.
• Thorne Vitamin K2 liquid — NSF certified, useful for malabsorption.
• Sports Research MK-7 — coconut oil base, soy-free, MenaQ7-based.
• Jarrow Formulas MK-7 — MenaQ7-based, tested.
• Bronson Vitamin K Triple Play — K1 + MK-4 + MK-7 for those who want full spectrum.
• Avoid: products without third-party testing, products that don't specify all-trans MK-7, products under $10 for a 90-day MK-7 supply (likely underdosed/non-trans).

Storage

• Room temperature (15-25 °C / 59-77 °F), dry, away from direct sunlight; vitamin K (especially K1) is light-sensitive. Opaque bottles preferred. Refrigeration not required; freezing not recommended. Shelf life 2-3 yrs unopened, 12-18 months opened.

Palatability

• Essentially tasteless in capsule/tablet form. Natto-derived liquid MK-7 may have a faint fermented note; not noticeable in capsule. Can be taken with any beverage.

Circadian & Exercise

• No strong circadian preference. Bone remodeling peaks overnight, which theoretically favors evening dosing, but no RCT demonstrates timing matters. Take with largest fat-containing meal for absorption.
• Exercise alignment: weight-bearing exercise + K2 + D3 is the complete bone-loading bundle. No evidence that timing K around a workout matters.

Reference Ranges

• Plasma phylloquinone: 0.29-2.64 nmol/L adults (optimal >1.0 nmol/L).
• PT: 11-13.5 s; INR: 0.8-1.2.
• Undercarboxylated osteocalcin (ucOC): optimal <20% of total osteocalcin (specialty labs only).
• PIVKA-II: <2 ng/mL (research/oncology labs).
• Dp-ucMGP: rising literature in CV and HF; reference ranges still being established.

Cost

What We Don't Know

• Whether any dose of K2 supplementation reduces hard cardiovascular endpoints (MI, stroke, mortality) in an RCT. AVADEC was null on primary AVC progression; no trial is powered for events.
• Whether MK-4 45 mg/d delivers Japanese-trial fracture reduction in Western populations (Binkley 2009 said no at 12 mo).
• Whether the ~30% "MK-7 sensitive" palpitations cluster reported in forums has a real biological basis or reflects pooled noise.
• Whether the D3:K2 ratio mythology (1,000 IU D3 : 10 mcg K2) has any evidence basis.
• Whether K2 can reverse established CAC (Kahn MD argues no; no RCT has shown reversal).
• Whether the ferroptosis axis translates to human clinical benefit in any indication.
• Whether dp-ucMGP cut-offs should drive supplementation decisions outside CKD/HF.
• Whether MK-9 through MK-13 from fermented foods and gut bacteria contribute meaningfully to vitamin K status.
• Whether GGCX pharmacogenomic variants should guide K dosing outside warfarin initiation.

References

Landmark & Western-population RCTs / Meta-analyses

1. Cockayne S, Adamson J, et al. (2006). Vitamin K and the prevention of fractures: systematic review and meta-analysis of RCTs. Arch Intern Med 166(12):1256-1261. PMID: 16801507
2. Knapen MH, Drummen NE, et al. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int 24(9):2499-2507. PMID: 23525894
3. Knapen MH, Braam LA, et al. (2015). Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. Thromb Haemost 113(5):1135-1144. PMID: 25694037
4. Geleijnse JM, Vermeer C, et al. (2004). Dietary intake of menaquinone is associated with reduced risk of CHD: Rotterdam Study. J Nutr 134(11):3100-3105. PMID: 15514282
5. Shea MK, O'Donnell CJ, et al. (2009). Vitamin K supplementation and progression of CAC. Am J Clin Nutr 89(6):1799-1807. PMID: 19386744
6. Beulens JW, Bots ML, et al. (2009). High dietary menaquinone intake associated with reduced coronary calcification. Atherosclerosis 203(2):489-493. PMID: 18722618
7. Booth SL, Broe KE, et al. (2003). Vitamin K intake and BMD in women and men (Framingham Offspring). Am J Clin Nutr 77(2):512-516. PMID: 12540415
8. Yoshida M, Jacques PF, et al. (2008). Effect of vitamin K supplementation on insulin resistance in older adults. Diabetes Care 31(11):2092-2096. PMID: 18650371
9. Binkley N, Harke J, et al. (2009). Vitamin K treatment reduces ucOC but does not alter BMD in postmenopausal North American women. J Bone Miner Res 24(6):983-991. PMID: 19113922
10. Westenfeld R, Krueger T, et al. (2012). Effect of K2 supplementation on functional K deficiency in hemodialysis. Am J Kidney Dis 59(2):186-195. PMID: 22169620
11. Schurgers LJ, Teunissen KJ, et al. (2007). K1 vs natto-derived MK-7: bioavailability comparison. Blood 109(8):3279-3283. PMID: 17158229

Guidelines & Cochrane

12. AAP Committee on Fetus and Newborn (2003). Controversies concerning vitamin K and the newborn. Pediatrics 112(1):191-192. PMID: 12837888
13. Pratt VM et al. (2020). AMP/CAP Clinical Warfarin Genotyping Allele Selection. J Mol Diagn. PMID: 32380173
14. Douketis JD, Spyropoulos AC, et al. (2022). ACCP/CHEST Perioperative Management of Antithrombotic Therapy. Chest. PMID: 35964703, 35964704
15. Abraham NS (2022). ACG-CAG on Anticoagulants/Antiplatelets during Acute GI Bleeding. Am J Gastroenterol. PMID: 35297395
16. Galliazzo S et al. (2024). FCSA Italy — Optimal Management of VKA. Thromb Haemost. PMID: 38626900
17. Ardell S et al. (2018). Cochrane — Prophylactic vitamin K in preterm neonates. PMID: 29401369
18. Jagannath VA, Fedorowicz Z, et al. (2020). Cochrane — K for cystic fibrosis. PMID: 32497260
19. Salazar CA et al. (2025). Cochrane — Factor Xa inhibitors vs LMWH/VKA VTE hip/knee. PMID: 39868562

2024-2026 Clinical & Mechanistic Updates

20. Wen et al. (2025). Habitual natto intake → serum MK-7 + osteocalcin carboxylation + BMD — meta-analysis. Front Nutr. PMID: 41393956
21. Zhang et al. (2025). K2 supplementation and bone turnover markers in postmenopausal osteoporosis. Front Endocrinol. PMID: 41268154
22. Xie et al. (2024). K supplementation on BMD at different sites in middle-aged / elderly. Bone Joint Res. PMID: 39657786
23. Zhang et al. (2025). PTH 1-34 + K2 combo therapy in postmenopausal osteoporosis. Horm Metab Res. PMID: 39197463
24. Kaneyasu et al. (2025). Menatetrenone suppressive effect on BMD loss after uterine cancer radiotherapy. Jpn J Radiol. PMID: 39849242
25. Zhang et al. (2025). K2 protects osteoblasts from glucocorticoid-induced ferroptosis via NRF2/FSP1. Drug Des Devel Ther. PMID: 41458254
26. Vesa et al. (2026). VKORC1 polymorphisms and osteopenia/osteoporosis — meta-analysis. Medicina. PMID: 41597466
27. Hasific et al. (2025). AVADEC substudy: K2+D3 on epicardial adipose tissue + systemic inflammation. Atherosclerosis. PMID: 41100911
28. de Vries et al. (2025). 1-yr MK-7 on vascular stiffness + BP in postmenopausal women. Nutrients. PMID: 40077685
29. Diederichsen ACP et al. (2022). MK-7 + D on aortic valve calcification — AVADEC RCT. Circulation. PMID: 35465686
30. Vidula MK et al. (2026). dp-ucMGP associated with adverse outcomes in heart failure. Circ Heart Fail. PMID: 41603031
31. Viegas CSB et al. (2026). Bioengineered EVs loaded with γ-carboxylated GRP modulate inflammation + vascular calcification. Biomater Adv. PMID: 41861711
32. Chen et al. (2025). VKORC1 polymorphisms predict arterial stiffness + MGP in CKD. Genes. PMID: 41465069
33. Lima et al. (2026). Poor K status + inflammation + gut microbiota in hemodialysis. J Nutr Biochem. PMID: 41052658
34. Naiyarakseree et al. (2023). MK-7 on arterial stiffness in chronic hemodialysis — multicenter RCT. Nutrients. PMID: 37299386
35. Yamada et al. (2025). MK-4 inhibits atherosclerotic plaque formation in ApoE-/- mice via oxLDL uptake. Eur J Pharmacol. PMID: 40683443
36. Zhou et al. (2025). MK-4 ameliorates abdominal aortic aneurysm via NRF2/GCLM (ferroptosis). Gene. PMID: 40992546
37. de Moraes et al. (2025). K2 and clinical outcomes in HCC — meta-analysis with trial sequential analysis. Nutr Cancer. PMID: 41388930
38. Guo et al. (2026). Role of vitamin K in HCC prognosis — systematic review / MA. Front Oncol. PMID: 41930200
39. Ishizuka M et al. (2012). Menatetrenone on HCC recurrence after resection RCT. World J Surg. PMID: 23225445
40. Ahmed et al. (2026). Differential effects of K across glycemic outcomes (prediabetes vs T2D). Nutrients. PMID: 41599883
41. Nikpayam et al. (2025). MK-7 on anthropometrics, glycemic indices, lipids — MA of RCTs. Prostaglandins. PMID: 40054729
42. Zhang et al. (2025). K2 alleviates insulin-resistance-associated muscle atrophy via AKT/mTOR. J Cachexia Sarcopenia Muscle. PMID: 40464168
43. Ding et al. (2025). MK-4 ameliorates diabetic osteoporosis via endothelial mitophagy. Drug Des Devel Ther. PMID: 40160965
44. Shea MK et al. (2026). Dietary intake, blood biomarkers + postmortem brain tissue K/D in older adults. J Nutr. PMID: 41722817
45. He et al. (2025). K-Trolox hybrid neuroprotectant — AD mouse, anti-ferroptotic. Eur J Med Chem. PMID: 40839917
46. Xia et al. (2025). Phylloquinone attenuates OGD-induced neuronal injury via xCT/GPX4. Neurochem Res. PMID: 41296108
47. Tan et al. (2026). VKORC1L1 downregulation → K-cycle disorder → neuronal ferroptosis in SCI. Mol Neurobiol. PMID: 41609979
48. Abass et al. (2026). K1 attenuates APAP ferroptotic hepatic damage via Keap1/Nrf2/HO-1. PMID: 41055715
49. Dai et al. (2025). K and antagonist in ferroptosis-damaged RPE-mediated CNV. Cell Death Dis. PMID: 40108164
50. Shi et al. (2025). Vitamin K as anti-ferroptotic drug for osteoarthritis via Gas6 (FDA drug screen). J Pharm Anal. PMID: 40496065
51. Lithgow et al. (2026). TAKEOVER RCT — K2 on recovery from muscle-damaging resistance exercise. Med Sci Sports Exerc. PMID: 41843412
52. Han et al. (2026). K intake + physical function, handgrip, mortality — NHANES 2003-2016. Nutr Res Pract. PMID: 41970326
53. Atieh et al. (2025). K2 + D3 improve long COVID, fungal translocation, inflammation — RCT. Nutrients. PMID: 39861434
54. Vilkoite et al. (2026). Colorectal adenoma presence + decreased menaquinone pathway in gut microbiome. PLoS One. PMID: 41811805
55. Zhang et al. (2026). Structural basis for carboxylation + epoxidation of human GGCX. Nat Commun. PMID: 41888148
56. Wu et al. (2025). Structural insight into bicarbonate-mediated carboxylation by human K-dependent carboxylase. Nat Commun. PMID: 41290650
57. Shen et al. (2026). Small-molecule GGCX inhibitor as novel anticoagulant strategy. Blood Adv. PMID: 41428972

Neonatal & pregnancy updates

58. Jacobs et al. (2026). Vitamin K deficiency bleeding after refusal — a sentinel event in a misinformation era. Pediatrics. PMID: 41916583
59. Scott et al. (2026). Trends in vitamin K administration among infants. JAMA. PMID: 41359326
60. Vazquez et al. (2026). Large ICH in setting of K prophylaxis refusal. Childs Nerv Syst. PMID: 41514043
61. Laubscher et al. (2026). Swiss oral neonatal K prophylaxis 2018-2024, guidelines valid. Eur J Pediatr. PMID: 41545738
62. Masuda et al. (2026). Prepregnancy obesity as independent risk factor for neonatal K deficiency. Nutrition. PMID: 41076804
63. Saad et al. (2026). Maternal phylloquinone intake and early neurodevelopment. Pediatr Res. PMID: 41530486

Retraction & pharmacogenomics

64. Tan et al. (2024) — ORIGINAL RCT K2 for nocturnal leg cramps. JAMA Intern Med. PMID: 39466236 — RETRACTED
65. Notice of Retraction and Replacement (2025). JAMA Intern Med. PMID: 40314950
66. Al Hamad et al. (2025). CYP2C9/VKORC1 polymorphisms in Saudi population. Medicina. PMID: 41155858