Vitamin K1 (Phylloquinone)
Also called phylloquinone, phytonadione, phytomenadione, vitamin K-1.
Best grade C across 7 graded outcomes Vitamin Last checked
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The short answer
From 12 sourcesVitamin K1 is needed to activate clotting proteins and bone proteins such as osteocalcin. Three large trials found that K1 supplements (0.5 to 5 mg a day for 1 to 4 years) did not slow bone loss in calcium- and vitamin D-replete older adults. People on warfarin need a steady vitamin K intake.
Quick pick
From a partner brand · paid link
Solaray Vitamin K, 100 mcg, 100 Tabs
from HerbsPro
Label: 1 tablet: 100 mcg vitamin K (as phylloquinone).
Best for trying one bottle: $7.29 one-time (checked Oct 15, 2026).
Every graded outcome on this page
7 rows · line = participants- CGrade CClinical fractures (secondary outcome)Fracturesn 440
- CGrade CCoronary artery calcium progressionArterial calcificationn 388
- CGrade CInsulin resistance (HOMA-IR)Insulin resistancen 355
- DGrade DCoronary artery calcium progression in people on hemodialysisArterial calcificationn 69
- ∅No effectBone mineral density at lumbar spine and total hipBone densityn 440
- ∅No effectBone mineral density at hip, spine and whole bodyBone densityn 401
- ∅No effectBone turnover, density and hip geometryBone densityn 381
- 4 more graded outcomes, in the evidence chapter
Key facts
- What it is
- The plant form of vitamin K; phytonadione is the synthetic K1 used in supplements1
- Adequate Intake
- 120 mcg a day for men and 90 mcg for women (adults); no upper limit has been set1
- Top studied outcome
- Bone mineral density: no benefit in three trials of 381 to 452 people (graded no-effect)245
- Fracture signal
- In one 440-woman trial, fewer clinical fractures occurred on 5 mg K1 (9 vs 20), but the trial was not powered for fractures4
- Warfarin
- Sudden changes in vitamin K intake can raise or lower the effect of warfarin and similar anticoagulants1
- Status in the U.S.
- Most U.S. diets supply enough; deficiency in adults is very rare1
What it is
Vitamin K1 (phylloquinone) is the main dietary form of vitamin K, found mostly in leafy greens and vegetable oils.
How it works
EstablishedForms, side by side
3 forms named in our sources. The rest show what our data holds, and say plainly where it holds nothing yet.
Vitamin K1 (Phylloquinone) forms compared
3 forms| 3 forms | Phylloquinone / phytonadione supplements | Leafy greens and vegetable oils | Menadione (vitamin K3) |
|---|---|---|---|
| Absorption in people | Free phylloquinone is about 80% absorbed. One study found phytonadione and MK-7 supplements both well absorbed, with MK-7 lasting longer in blood.1 | K1 in plants is bound to chloroplasts: the body absorbs only 4% to 17% as much from spinach as from a tablet. Eating vegetables with some fat helps.1 | No human absorption data in our sources.1 |
| GI tolerance | No adverse effects from food or supplement vitamin K have been reported, per the Food and Nutrition Board.1 | Food sources are the main way most people meet the Adequate Intake.1 | Damaged liver cells in laboratory studies, so it is no longer used in dietary supplements or fortified foods.1 |
| Studied for | Bone density, arterial calcification and insulin resistance (0.5 to 5 mg a day; 10 mg three times a week in hemodialysis) | Observational studies of intake and bone | Not used in supplements |
- Phylloquinone / phytonadione supplements
- Absorption in people
- Free phylloquinone is about 80% absorbed. One study found phytonadione and MK-7 supplements both well absorbed, with MK-7 lasting longer in blood.1
- GI tolerance
- No adverse effects from food or supplement vitamin K have been reported, per the Food and Nutrition Board.1
- Studied for
- Bone density, arterial calcification and insulin resistance (0.5 to 5 mg a day; 10 mg three times a week in hemodialysis)
- Leafy greens and vegetable oils
- Absorption in people
- K1 in plants is bound to chloroplasts: the body absorbs only 4% to 17% as much from spinach as from a tablet. Eating vegetables with some fat helps.1
- GI tolerance
- Food sources are the main way most people meet the Adequate Intake.1
- Studied for
- Observational studies of intake and bone
- Menadione (vitamin K3)
What the human research says
Human trials only, one row per outcome. The form line shows what each trial actually tested. Grades follow our evidence-grading policy.
Trial map
7 graded outcomes, largest study first7 graded outcomes: 1 improved, 1 mixed, 5 no effect. The largest, a 2008 randomized trial of 440 people on clinical fractures (secondary outcome), found an improvement.
1Clinical fractures (secondary outcome)
Improved · Grade C · RCT, 440 people, 2008
Postmenopausal women with osteopenia (ECKO trial)
Dose, result and source| Outcome | Found | People | Study | Who was studied |
|---|---|---|---|---|
| Clinical fractures (secondary outcome) | Improved | 440 | Grade C · RCT, 2008 | Postmenopausal women with osteopenia (ECKO trial) |
| Bone mineral density at lumbar spine and total hip | No effect | 440 | No-effect grade · RCT, 2008 | Postmenopausal women with osteopenia, vitamin D replete (ECKO trial, Canada) |
| Bone mineral density at hip, spine and whole body | No effect | 401 | No-effect grade · RCT, 2008 | Men and women aged 60 to 80 who were calcium and vitamin D replete (452 randomized) |
| Coronary artery calcium progression | No effect | 388 | Grade C · RCT, 2009 | Healthy older men and postmenopausal women |
| Bone turnover, density and hip geometry | No effect | 381 | No-effect grade · RCT, 2009 | Healthy, non-osteoporotic postmenopausal North American women |
| Insulin resistance (HOMA-IR) | Mixed | 355 | Grade C · RCT, 2008 | Older adults without diabetes (ancillary analysis of the bone-loss trial) |
| Coronary artery calcium progression in people on hemodialysis | No effect | 69 | Grade D · Pilot RCT, 2023 | Adults on hemodialysis with a coronary calcium score of 30 or more (iPACK-HD, Canada; 86 randomised) |
Every graded row
7 rowsShowing 7 of 7 outcomes. Human trials only.
CGrade CClinical fractures (secondary outcome)FracturesImprovedRCT
n 440 · 2008
Improved Fewer women on vitamin K1 had clinical fractures (9 vs 20, p = 0.04). The authors note the trial was not powered for fractures and the numbers were small.
- Design
- RCT, n = 440, 2008
- Population
- Postmenopausal women with osteopenia (ECKO trial)
- Form
- Vitamin K1
- Dose
- 5 mg/day
- Duration
- 2 to 4 years
- Source
- Reference 4 · PubMed 18922041 (opens PubMed)
CGrade CCoronary artery calcium progressionArterial calcificationNo effectRCT
n 388 · 2009
No effect No difference in calcium-score progression by intention to treat (mean change 27 vs 37 Agatston units). In adherent participants and in those with existing calcification, progression was smaller on phylloquinone; the authors call this hypothesis-generating.
- Design
- RCT, n = 388, 2009
- Population
- Healthy older men and postmenopausal women
- Form
- Phylloquinone in a multivitamin
- Dose
- 500 mcg/day vs multivitamin alone
- Duration
- 3 years
- Source
- Reference 3 · PubMed 19386744 (opens PubMed)
CGrade CInsulin resistance (HOMA-IR)Insulin resistanceMixedRCT
n 355 · 2008
Mixed The effect differed by sex: HOMA-IR was lower in men on vitamin K than men on control, with no difference in women.
- Design
- RCT, n = 355, 2008
- Population
- Older adults without diabetes (ancillary analysis of the bone-loss trial)
- Form
- Phylloquinone
- Dose
- 500 mcg/day
- Duration
- 36 months
- Source
- Reference 6 · PubMed 18697901 (opens PubMed)
DGrade DCoronary artery calcium progression in people on hemodialysisArterial calcificationNo effectPilot RCT
n 69 · 2023
No effect Phylloquinone cut dephospho-uncarboxylated MGP by 86% and raised K1 levels and the carboxylated-to-uncarboxylated osteocalcin ratio versus placebo, but coronary calcification progressed no differently between groups.
- Design
- Pilot RCT, n = 69, 2023
- Population
- Adults on hemodialysis with a coronary calcium score of 30 or more (iPACK-HD, Canada; 86 randomised)
- Form
- Phylloquinone
- Dose
- 10 mg three times a week
- Duration
- 12 months
- Source
- Reference 8 · PubMed 35641194 (opens PubMed)
∅No effectBone mineral density at lumbar spine and total hipBone densityNo effectRCT
n 440 · 2008
No effect Spine density fell 1.28% vs 1.22% and hip density 0.69% vs 0.88% (no difference). K1 raised blood K1 10-fold and lowered undercarboxylated osteocalcin. It was well tolerated, with no difference in adverse effects.
- Design
- RCT, n = 440, 2008
- Population
- Postmenopausal women with osteopenia, vitamin D replete (ECKO trial, Canada)
- Form
- Vitamin K1
- Dose
- 5 mg/day
- Duration
- 2 years (extended up to 4 years for some)
- Source
- Reference 4 · PubMed 18922041 (opens PubMed)
∅No effectBone mineral density at hip, spine and whole bodyBone densityNo effectRCT
n 401 · 2008
No effect No difference in bone density change at any site. Phylloquinone raised blood K1 and lowered undercarboxylated osteocalcin; no other bone marker differed.
- Design
- RCT, n = 401, 2008
- Population
- Men and women aged 60 to 80 who were calcium and vitamin D replete (452 randomized)
- Form
- Phylloquinone in a multivitamin
- Dose
- 500 mcg/day, with 600 mg calcium and 400 IU vitamin D in both groups
- Duration
- 3 years
- Source
- Reference 2 · PubMed 18252784 (opens PubMed)
∅No effectBone turnover, density and hip geometryBone densityNo effectRCT
n 381 · 2009
No effect Both vitamin K forms lowered undercarboxylated osteocalcin but did not change bone formation or resorption markers, spine or hip density, or hip geometry.
- Design
- RCT, n = 381, 2009
- Population
- Healthy, non-osteoporotic postmenopausal North American women
- Form
- Phylloquinone (1 mg) vs menatetrenone (MK-4, 45 mg) vs placebo
- Dose
- 1 mg/day phylloquinone; all groups got calcium and vitamin D3
- Duration
- 12 months
- Source
- Reference 5 · PubMed 19113922 (opens PubMed)
What the numbers add up to
Each point is worked out from the data and the sources numbered on this page, with the arithmetic shown under it. It adds no new data and is not medical advice.
Studied doses
Doses used in research, shown against the official limits. They describe the studies, not a recommendation for you.
Studied doses in research, not advice. These are amounts used in research, not personal advice. Your clinician or pharmacist can say what fits you.
Doses studied in human trials
NIH ODS updated Mar 29, 2021Doses studied in human trials ranged from 500 mcg of phylloquinone a day for 3 years to 5 mg a day for 2 to 4 years; most trials gave calcium and vitamin D to every group. A pilot trial in people on hemodialysis used 10 mg three times a week for 12 months.2458
Intake reference: Adequate Intake for adults: 120 mcg/day (men) and 90 mcg/day (women, including pregnancy and lactation; 75 mcg at ages 14 to 18). No UL was set because of low potential for toxicity.1 No UL; the Food and Nutrition Board reported no adverse effects from vitamin K in food or supplements. NIH ODS fact sheet (updated March 29, 2021).
Interactions and safety
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
What Vitamin K1 meets
4 cited rows 6 tested togetherMedicines 4
Supplements and foods 3
- Reference summary
- Tested together in a graded trial
Choose a medicine or supplement above to read its cited rows here.
Also cited: 6 tested together
Antibiotics
NIH fact sheetReference summaryCan lower levels
Antibiotics, for example Cephalosporins such as cefoperazone: May lower vitamin K status by killing vitamin K-producing gut bacteria; supplements are usually not needed unless use is prolonged and intake is poor.
Source 1, NIH Office of Dietary Supplements (2021)
Bile acid sequestrants
NIH fact sheetReference summaryCan lower levels
Bile acid sequestrants, for example Cholestyramine, colestipol: Can reduce absorption of vitamin K and other fat-soluble vitamins; ODS suggests monitoring status with long-term use.
Source 1, NIH Office of Dietary Supplements (2021)
Orlistat
NIH fact sheetReference summaryCan lower levels
Orlistat, for example Alli, Xenical: Reduces fat-soluble vitamin absorption; combined with warfarin it might markedly raise prothrombin time.
Source 1, NIH Office of Dietary Supplements (2021)
Warfarin and similar vitamin K antagonists
NIH fact sheetReference summary
Warfarin and similar vitamin K antagonists, for example Warfarin (Coumadin), phenprocoumon, acenocoumarol, tioclomarol: ODS describes a serious and potentially dangerous interaction: these anticoagulants work against vitamin K, and sudden changes in vitamin K intake from food or supplements can increase or decrease their effect, so intake should stay consistent.
Source 1, NIH Office of Dietary Supplements (2021)
CalciumCalcium page
Tested together
Bone mineral density at hip, spine and whole body. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
Tested together
Bone turnover, density and hip geometry. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
MultivitaminMultivitamin page
Tested together
Bone mineral density at hip, spine and whole body. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
Tested together
Coronary artery calcium progression. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
Vitamin D3 vs D2Vitamin D3 vs D2 page
Tested together
Bone mineral density at hip, spine and whole body. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
Tested together
Bone turnover, density and hip geometry. Graded on the Vitamin K1 page; tested together is not a claim that they work better together.
Interactions
4 agents| Agent | What the source says | Evidence |
|---|---|---|
| Medicines1 | ||
| Warfarin and similar vitamin K antagonistse.g. Warfarin (Coumadin), phenprocoumon, acenocoumarol, tioclomarol | ODS describes a serious and potentially dangerous interaction: these anticoagulants work against vitamin K, and sudden changes in vitamin K intake from food or supplements can increase or decrease their effect, so intake should stay consistent.1 | NIH fact sheet |
| Medicines that can lower levels3 | ||
| Antibioticse.g. Cephalosporins such as cefoperazone | May lower vitamin K status by killing vitamin K-producing gut bacteria; supplements are usually not needed unless use is prolonged and intake is poor.1 | NIH fact sheet |
| Bile acid sequestrantse.g. Cholestyramine, colestipol | Can reduce absorption of vitamin K and other fat-soluble vitamins; ODS suggests monitoring status with long-term use.1 | NIH fact sheet |
| Orlistate.g. Alli, Xenical | Reduces fat-soluble vitamin absorption; combined with warfarin it might markedly raise prothrombin time.1 | NIH fact sheet |
Check with what you take
Kept on this device onlyAdd what you take. We list every interaction our evidence profiles cite between Vitamin K1 and your picks, and between your picks.
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Add a supplement or medicine you take to check it against Vitamin K1.
Starting from one medicine? The interaction checker rates how serious each pair is, on a curated list of 19 entries for 11 medicines. This cabinet has no severity rating: it lists every interaction row our supplement pages cite.
Who should be careful
5 groups- People on warfarin or similar anticoagulants
- Keep vitamin K intake consistent and involve the prescriber before starting, stopping or changing a supplement, because intake changes alter the anticoagulant effect.1
- Malabsorption or bariatric surgery
- Cystic fibrosis, celiac disease, ulcerative colitis, short bowel syndrome and bariatric surgery can lower vitamin K status; ODS says these people might need monitoring and, in some cases, supplementation.1
- Liver disease
- LiverTox rates vitamin K an unlikely cause of liver injury (likelihood score E): neither normal nor high doses have been linked to liver enzyme rises or liver injury. It notes that people with cholestatic liver disease or cirrhosis may become low in vitamin K because absorption depends on bile.12
- Newborns
- Babies are born with low vitamin K because little crosses the placenta; the American Academy of Pediatrics recommends a single 0.5 to 1 mg vitamin K1 injection at birth.1
- Pregnancy and breastfeeding
- ODS sets the Adequate Intake at 90 mcg a day in pregnancy and breastfeeding (75 mcg at ages 14 to 18) and lists no pregnancy-specific risk; no upper limit has been set. LactMed says vitamin K occurs naturally in breast milk, maternal supplements are usually not needed, and a mother's supplement is not a safe substitute for the vitamin K injection newborns receive at birth.17
Safety
3 notesLow toxicity; the warfarin interaction is the main concern.
- Upper limit
- No UL has been set, because no adverse effects from vitamin K in food or supplements have been reported.1
- Trial tolerance
- 5 mg a day for 2 to 4 years was well tolerated, with adverse effects no different from placebo.4
- Anticoagulants
- Consistency matters more than amount for people on warfarin: sudden changes can push clotting times up or down.1
Food sources
How much one serving of each food supplies, each amount with its source.
Foods by amount per serving
Show the table, with sourcesHide the table
How to read the label
What to check on the Supplement Facts panel.
How to read the label
3 checksK1 vs K2 on the label
Labels may list phylloquinone or phytonadione (K1) or menaquinones such as MK-4 and MK-7 (K2). They are different compounds with different trial data.1
Label dose vs clinical dose
Check for calcium and vitamin D
ODS notes that vitamin D and calcium given alongside vitamin K can explain mixed bone results, so combination products are hard to compare with K1 alone.1
Where to buy Vitamin K1 (Phylloquinone)
Products from brands we partner with that contain Vitamin K1 (Phylloquinone). Check the amount per serving against the doses studied above, and the label for other ingredients.
Vitamin K1 (Phylloquinone) products from partner brands
1 product Paid links · we earn a commission- Quick pickHerbsProSolaray Vitamin K, 100 mcg, 100 Tabs
1 tablet: 100 mcg vitamin K (as phylloquinone)
$7.29one-timeChecked Oct 15, 2026
Frequently asked questions
Short answers to common questions; the numbers link to the sources below.
Common questions
7 answersDoes vitamin K1 strengthen bones?
Does vitamin K1 slow artery calcification?
In a 3-year trial of 388 older adults, 500 mcg a day did not slow coronary calcium overall; a subgroup signal was called hypothesis-generating.3
Does vitamin K1 have side effects?
How much vitamin K do adults need?
The Adequate Intake is 120 mcg a day for men and 90 mcg for women. Most U.S. diets already supply that.1
Can I use vitamin K1 with warfarin?
Only with the prescriber's involvement. Vitamin K counteracts warfarin, and sudden changes in intake can make clotting times unstable.1
Is vitamin K1 safe during pregnancy and breastfeeding?
How is K1 different from K2?
K1 (phylloquinone) comes mainly from leafy greens; K2 (menaquinones such as MK-4 and MK-7) comes from bacteria and fermented or animal foods. MK-7 stays in the blood longer than K1.1
Sources
12 sources: trial abstracts, NIH fact sheets and reference databases. Numbers in the text link here.
Sources cited on this page
12 sources- 1Vitamin K: Fact Sheet for Health ProfessionalsFact sheet NIH Office of Dietary Supplements, 2021 · ods.od.nih.gov
- 2Effect of vitamin K supplementation on bone loss in elderly men and women.RCT J Clin Endocrinol Metab, 2008 · PMID 18252784
- 3Vitamin K supplementation and progression of coronary artery calcium in older men and women.RCT Am J Clin Nutr, 2009 · PMID 19386744
- 4Vitamin K supplementation in postmenopausal women with osteopenia (ECKO trial): a randomized controlled trial.RCT PLoS Med, 2008 · PMID 18922041
- 5Vitamin K treatment reduces undercarboxylated osteocalcin but does not alter bone turnover, density, or geometry in healthy postmenopausal North American women.RCT J Bone Miner Res, 2009 · PMID 19113922
- 6Effect of vitamin K supplementation on insulin resistance in older men and women.RCT Diabetes Care, 2008 · PMID 18697901
- 7Vitamin KDatabase LactMed (NCBI Bookshelf), 2026 · ncbi.nlm.nih.gov
- 8Inhibit progression of coronary artery calcification with vitamin K in hemodialysis patients (the iPACK-HD study): a randomized, placebo-controlled multi-center, pilot trial.Pilot RCT Nephrol Dial Transplant, 2023 · PMID 35641194
- 9Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials.Meta-analysis Osteoporos Int, 2019 · PMID 31076817
- 10The effect of vitamin K supplementation on cardiovascular risk factors: a systematic review and meta-analysis.Meta-analysis J Nutr Sci, 2024 · PMID 38282652
- 11The Differential Effects of Vitamin K Across Glycaemic Outcomes in Prediabetes and Type 2 Diabetes Mellitus.Meta-analysis Nutrients, 2026 · PMID 41599883
- 12Vitamin KDatabase LiverTox (NCBI Bookshelf), 2021 · ncbi.nlm.nih.gov
What changed
Every dated change to this page: what changed, who made it and why.
Change log
3 entries| Date | Change | Who and why |
|---|---|---|
| evidence, studied doses, who should be careful, FAQ | Re-checked against the NIH ODS vitamin K fact sheet (updated 2021-03-29; warfarin wording unchanged). Added the iPACK-HD hemodialysis pilot trial (PMID 35641194, graded D). Added pooled context from meta-analyses on fractures (PMID 31076817) and insulin resistance (PMIDs 38282652, 41599883) to the existing rows. Added the LactMed vitamin K record to pregnancy and breastfeeding, plus FAQ answers on pregnancy and side effects. PubMed search for 2023 to 2026 K1 trials and meta-analyses found no other qualifying study. Added the LiverTox vitamin K record (likelihood score E) as a liver note. | Writer: Kymata Health EditorialTrigger: A–Z page audit |
| all | Initial editorial evidence review (first draft). Every PMID checked against NCBI E-utilities esummary (title and year) and each cited abstract read; numbers taken from the abstracts. Erratum check: the ECKO trial (PMID 18922041) has a linked erratum; no retractions found. Funding: the bone, calcium-score and insulin trials were NIH-funded; ECKO was publicly funded with vitamin K supplied by Roche Vitamins (now DSM) and Wyeth Foundation support for assays. Safety, interactions and pregnancy text come only from the ODS fact sheet. No product links. | Writer: Kymata Health EditorialTrigger: new page |
| evidence and safety | Adversarial review: warfarin interaction now uses ODS's wording (serious and potentially dangerous) and lists tioclomarol. | Writer: Kymata Health EditorialTrigger: adversarial review |
Supplement & Nutrient Encyclopedia. Educational information only; it is not medical advice and does not replace a clinician. Dietary supplements are not intended to diagnose, treat, cure or prevent any disease. Statements about supplements have not been evaluated by the FDA.