Vitamin K1
Phylloquinone
TL;DR
K1 is the form that runs blood clotting and is abundant in leafy greens; the bone and arterial claims people attach to "vitamin K" mostly come from K2 trials, and K1 supplementation has largely failed to reduce fractures.
Ideal For
- People with fat malabsorption or very low vegetable intake
- Newborns, via standard prophylactic injection
Avoid If
- You take warfarin and have not discussed it with your prescriber
- You are specifically seeking bone or arterial benefit — that evidence belongs to K2
Frequently Asked Questions
Overview
Phylloquinone is the vitamin K found in green vegetables, and it is the form your liver preferentially takes up to gamma-carboxylate clotting factors II, VII, IX and X. Frank deficiency is rare outside malabsorption, newborns and long-term antibiotic use, which is why the newborn K1 injection remains one of the most cost-effective preventive interventions in medicine. Where the picture gets muddled is bone and vascular health. Osteocalcin and matrix Gla protein also require vitamin K, but they are extrahepatic, and menaquinones (K2, especially MK-7) persist in circulation far longer and reach those tissues better. Trials reflect this: the ECKO trial gave 5 mg/day of K1 to 440 postmenopausal women for two to four years and found no improvement in bone mineral density, while K2 trials have shown more consistent, if still debated, fracture signals. K1 is also the reason warfarin users are told to keep leafy-green intake steady rather than avoid it.
How It Works
- Cofactor for gamma-glutamyl carboxylase, activating clotting factors II, VII, IX, X
- Carboxylates osteocalcin, though less efficiently in bone than menaquinones
- Recycled through the vitamin K epoxide reductase cycle that warfarin blocks
Quick Facts
- One cup of cooked kale supplies many times the daily adequate intake
- ECKO trial: 5 mg/day K1 for up to 4 years did not improve bone density
- Warfarin patients need consistent, not zero, vitamin K intake
Benefits & Outcomes
No linked outcomes yet. Research is ongoing.
Supporting Research14 studies
Vitamin K supplementation and vascular calcification in people with type 2 diabetes and chronic kidney disease: a randomized controlled trial
Zwakenberg SR, de Jong PA, Bartstra JW +3 more
Vitamin K status improved markedly but there was no difference in femoral artery or coronary calcification progression versus placebo.
Vitamin K2 supplementation does not influence bone loss in early menopausal women: a randomised double-blind placebo-controlled trial
Emaus N, Gjesdal CG, Almås B +5 more
No significant difference in bone mineral density change at any measured site despite improved vitamin K status markers.
Vitamin K2 and bone health: a systematic review
Iwamoto, I., Kosha, S., Noguchi, S.
Review of vitamin K2 (menaquinone) trials, dominated by Japanese studies of high-dose MK-4 (45 mg/day), reported improved bone mineral density maintenance and reduced vertebral and non-vertebral fracture rates in postmenopausal and osteoporotic women, with effects on bone quality via osteocalcin carboxylation rather than density alone.
Evaluation of the clinical efficacy and safety of an eye counter pad containing caffeine and vitamin K in emulsified Emu oil triglycerides
Ahmadraji F, Shatalebi MA
Significant reduction in infraorbital pigmentation and wrinkle depth versus baseline and control side.
Accelerated resolution of laser-induced bruising with topical 20% arnica: a rater-blinded randomized controlled trial
Leu S, Havey J, White LE +4 more
Topical 20% arnica ointment reduced laser-induced bruising more than white petrolatum and 1% vitamin K formulations.
Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women
Knapen MH, Drummen NE, Smit E +2 more
MK-7 improved vitamin K status, decreased age-related decline in lumbar spine and femoral neck bone mineral density and reduced vertebral height loss.
Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study
Geleijnse JM, Vermeer C, Grobbee DE +5 more
Highest tertile of menaquinone intake was associated with reduced coronary heart disease mortality, all-cause mortality and severe aortic calcification; phylloquinone intake showed no association.
Effect of vitamin K supplementation on bone loss in elderly men and women
Booth SL, Dallal G, Shea MK +3 more
Phylloquinone reduced undercarboxylated osteocalcin but produced no difference in bone mineral density.
Daily vitamin K supplementation improves anticoagulant stability
Rombouts EK, Rosendaal FR, van der Meer FJ
Daily supplementation with 100 microgram of vitamin K improved the stability of anticoagulation in patients with unstable control.
Does vitamin K cream reduce laser-induced purpura?
Shah NS, Lazarus MC, Bugdodel R
Topical vitamin K after laser modestly reduced purpura severity.
Vitamin K supplementation in postmenopausal women with osteopenia (ECKO trial): a randomized controlled trial
Cheung AM, Tile L, Lee Y +3 more
Daily 5 mg vitamin K1 did not protect against bone mineral density loss in postmenopausal women with osteopenia.
Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials
Mott A, Bradley T, Wright K +5 more
No consistent effect of vitamin K on bone mineral density; fracture reductions were confined to lower-quality trials.
Vitamin K supplementation and progression of coronary artery calcium in older men and women
Shea MK, O'Donnell CJ, Hoffmann U +6 more
Vitamin K1 did not slow coronary artery calcium progression in the intention-to-treat analysis.
Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials
Cockayne S, Adamson J, Lanham-New S +3 more
Vitamin K supplementation was associated with improved bone density in all but one trial.
Safety Information
Potential Side Effects
Very well tolerated. No established toxicity for oral phylloquinone.
Contraindications
Anyone on warfarin or other vitamin K antagonists must not change intake without clinician guidance — K1 directly opposes the drug.
Drug Interactions
- Warfarin and other vitamin K antagonists
- Orlistat and bile acid sequestrants reduce absorption
Pregnancy & Breastfeeding
Pregnancy: likely_safe
Breastfeeding: likely_safe
Dosage Guidelines
Dosage Used in Studies
Consult healthcare provider
Best Time to Take
With the largest meal of the day
Best Form
Dietary leafy greens; supplement only for documented need
Bioavailability
Poorly absorbed from raw vegetables (roughly 5-10%); much better from oil-based supplements or cooked greens with fat
Forms Compared
Plant form; hepatic priority, short half-life
Different tissue distribution; where most bone and arterial evidence sits
Food & Timing
With a fat-containing meal
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.