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Vitamin K1 (Phylloquinone)
The plant form of vitamin K — ESSENTIAL and well-proven for blood clotting (it activates clotting factors). As a supplement for bone/cardiovascular health it's only modestly evidenced, and weaker than vitamin K2 for those uses.
What the evidence says
Most Vitamin K1 studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality meta-analyses and randomised trials published 1986–2026 with a typical study size of 35 participants.
Based on 87 studies · 4 meta-analyses · 75 RCTs · 35 total participants
Confidence
High confidenceBy outcome
K1's coagulation role is well established, but as a bone or cardiovascular supplement it rests on a tiny evidence base with no meta-analyses and a small RCT showing little BMD benefit.
82 rigorous studies
78 randomized trials · 4 meta-analyses · 1 systematic reviews
Our evidence rating for Vitamin K1 is accountable to this entire body of rigorous research indexed in PubMed — not a hand-picked subset.
PubMed · as of Jul 2026
7 trials ongoing or recruiting · 47 completed on ClinicalTrials.gov
3 of the completed trials have posted results
Registered trials show research momentum for Vitamin K1, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Vitamin K1 meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Vitamin K contributes to normal blood clotting”
“Vitamin K contributes to the maintenance of normal bones”
Not authorised by EFSA
“Vitamin K1 + K2 Vitamin K1 and K2 supports a healthy heart Vitamin K1 and K2 stimulates blood clotting”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Vitamin K1 (phylloquinone) is the plant form of vitamin K, abundant in leafy greens. Its essential, well-established role is in blood coagulation: it's the cofactor that activates clotting factors II, VII, IX, and X (which is why it's used clinically to reverse warfarin and treat bleeding).
As a supplement for bone density or cardiovascular health, the evidence is modest and generally weaker than vitamin K2 (menaquinone), which is preferentially used for extra-hepatic tissues like bone and arteries. Most people get adequate K1 from diet; supplemental K1 is most relevant for documented insufficiency.
NOTE: vitamin K interacts strongly with warfarin.
Cofactor for gamma-carboxylation that activates clotting factors II, VII, IX, X.
Activates osteocalcin for bone mineralization (K2 does this more efficiently in bone).
Each carboxylation oxidises vitamin K, and vitamin K epoxide reductase (VKORC1) regenerates it — which is the enzyme warfarin blocks. That shared step is why K1 intake and vitamin-K-antagonist dosing pull directly against each other.
How Vitamin K1 works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Do NOT change vitamin K intake without clinician guidance — it alters anticoagulation.
Usually met through diet (leafy greens).
Vitamin K directly opposes warfarin — changing intake destabilizes INR. Keep intake consistent and inform your clinician.
Tip: Oral forms are well tolerated
Vitamin K1 has an evidence score of 4/10 — emerging evidence based on 12 indexed studies. The plant form of vitamin K — ESSENTIAL and well-proven for blood clotting (it activates clotting factors). As a supplement for bone/cardiovascular health it's only modestly evidenced, and weaker than vitamin K2 for those uses. Representative study: PMID 28403946.
The commonly studied dose of Vitamin K1 is Dietary adequacy ~90-120mcg/day; supplements often 100-500mcg. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Vitamin K1 is with meals. Take it with food. Fat-soluble — take with a fat-containing meal.
Vitamin K1 is generally safe at recommended doses, with a few precautions worth noting. Reported side effects are uncommon and include allergic reaction (rare, IV forms). Use caution if any of these apply to you: Warfarin / vitamin-K-antagonist anticoagulant use (major interaction); Starting, stopping or changing the dose while on a vitamin-K antagonist without INR monitoring — the IOM's advice to anticoagulated patients is to keep to their normal, steady intake.
Vitamin C
Likely helpsHumans cannot synthesize this vitamin — required for collagen production, immune cell function, and iron absorption; athletes need more.
Vitamin B12
Likely helpsDrives nerve myelination, red blood cell formation, and DNA synthesis — deficiency is common in vegans, vegetarians, and older adults.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
B-Complex
Probably helpsEssential B vitamins in their active methylated forms, supporting energy production, mood, and cognitive function.
Explore: Best supplements for Body Health
Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 87 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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