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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 vitamin K2 has not shown a consistent bone or arterial benefit either.
What the evidence says
Vitamin K1 doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1986–2026 with a typical study size of 35 participants.
Based on 88 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.
74 randomised trials
82% were about Vitamin K1 in an audit of 50 of them
Every randomised or controlled trial of Vitamin K1 indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Sep 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momentum for Vitamin K1, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed.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 Oct 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. Vitamin K2 (menaquinone) reaches extra-hepatic tissues like bone and arteries more readily, but its trials have not shown a consistent bone or arterial benefit either.
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.
Carboxylates osteocalcin, a bone protein that binds calcium. Whether this makes bones stronger has not been shown.
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 88 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 vitamin K2 has not shown a consistent bone or arterial benefit either. Representative study: PMID 28403946.
Dosing for Vitamin K1: Dietary adequacy ~90-120mcg/day; supplements often 100-500mcg (a typical label dose, not the dose used in the cited trial, which used 1,000 mcg a day). 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 has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Reported side effects include allergic reaction (rare, IV forms). How often they occur is not established for all of them. 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 88 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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