Overview
Vitamin K1, scientifically known as phylloquinone, is the plant-derived form of vitamin K found naturally in leafy green vegetables, cruciferous vegetables, and other plant sources. As a dietary supplement, it has gained attention not only for its well-established role in blood coagulation but also for its broader effects on bone metabolism, cardiovascular health, and metabolic function.
Unlike its cousin vitamin K2 (menaquinone), which is produced by bacteria and found in fermented foods and animal products, vitamin K1 is the predominant form in the food supply and the primary target of supplementation research. It serves as an essential cofactor for activating multiple clotting factors—specifically factors II, VII, IX, and X—making it critical for hemostasis (blood clotting). Clinically, vitamin K1 is used to reverse anticoagulant overdose and treat vitamin K deficiency bleeding in newborns.
This comprehensive guide examines the evidence for vitamin K1 supplementation across multiple health domains, from its proven effects on coagulation to its emerging roles in metabolic and cognitive health.
How Vitamin K1 Works: Mechanism of Action
Vitamin K1 functions as a cofactor for the enzyme gamma-glutamyl carboxylase, which catalyzes a critical chemical reaction in the body. Specifically, this enzyme carboxylates glutamic acid residues on vitamin K-dependent proteins, enabling these proteins to bind calcium ions and become functionally active.
This carboxylation process is essential for:
- Coagulation: Activation of clotting factors II, VII, IX, and X, as well as the anticoagulant proteins C and S, which maintain the balance between blood clotting and bleeding
- Bone metabolism: Activation of osteocalcin and matrix Gla protein, which regulate bone mineralization and vascular calcification
- Vascular health: Prevention of arterial calcification through carboxylation of matrix Gla protein
After catalyzing this carboxylation reaction, vitamin K1 is converted to vitamin K epoxide. This epoxide is then recycled back to active vitamin K1 by the enzyme vitamin K epoxide reductase complex (VKORC1). This recycling pathway is crucial—warfarin and related anticoagulant drugs work by inhibiting VKORC1, thereby reducing the availability of active vitamin K and lowering clotting factor production.
Understanding this mechanism explains why vitamin K1 and warfarin have such a significant drug-nutrient interaction: consistent vitamin K1 intake is essential for those on warfarin therapy to maintain stable anticoagulation.
Evidence by Health Goal
Blood Coagulation & Hemostasis
Evidence Tier: Tier 1 (Gold Standard)
Vitamin K1's role in blood coagulation is the most well-established and clinically validated effect. This is not a debated area—vitamin K1 is essential for the synthesis of clotting factors, and supplementation is a standard medical treatment for vitamin K deficiency and anticoagulant overdose.
Fat Loss & Metabolic Health
Evidence Tier: Tier 2 (Suggestive But Unproven)
Vitamin K1 has not been proven to directly improve fat loss in humans. However, observational studies suggest associations between higher vitamin K1 intake and better metabolic markers. In a study of 101 men with high fat mass, phylloquinone intake negatively correlated with HOMA-β (a marker of insulin secretion), suggesting a potential relationship with insulin secretion regulation. In 122 women with high fat mass, phylloquinone intake correlated negatively with fasting insulin and HOMA-β by 20.7% (p=0.026), indicating potential benefits for insulin control.
These associations are intriguing but observational, meaning causation cannot be established. No randomized controlled trials demonstrate that vitamin K1 supplementation causes weight loss or fat reduction.
Energy & Glucose Metabolism
Evidence Tier: Tier 2 (Suggestive But Unproven)
One small human RCT provides encouraging but preliminary evidence. In 82 prediabetic women, vitamin K1 supplementation at 1,000 μg daily for four weeks reduced 2-hour post-oral glucose tolerance test (OGTT) glucose by 1.3 mmol/L (7.32 vs 8.62 mmol/L, p<0.05) and insulin levels by 32 μIU/mL (80.34 vs 112.43 μIU/mL, p<0.05). The same trial showed that vitamin K1 increased carboxylated osteocalcin (12.53±5.95 vs 7.43±4.85 ng/ml, p<0.001), suggesting improved metabolic osteocalcin function.
However, this is a single small study with a short intervention period. Larger, longer-term trials are needed to confirm these findings apply broadly.
Hormonal Balance & Insulin Sensitivity
Evidence Tier: Tier 3 (Probable Association)
Evidence for vitamin K1's role in hormonal balance remains inconsistent. In prediabetic women (n=82, 4-week RCT), vitamin K1 (1,000 μg daily) reduced 2-hour post-OGTT insulin by 28% and increased the insulin sensitivity index by 40%. In contrast, a 12-month RCT in 42 postmenopausal women found that vitamin K1 (1 mg daily) reduced undercarboxylated osteocalcin but did not significantly improve HOMA-IR (insulin resistance index) compared to placebo.
This inconsistency suggests that vitamin K1 may support metabolic health through multiple mechanisms, but effects are not uniform across populations or study designs.
Bone Health & Injury Recovery
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows biochemical effects on bone metabolism markers in humans, but evidence for actual improvement in injury recovery is limited and inconsistent. Most positive findings relate to bone turnover markers rather than clinical outcomes like fracture healing or recovery speed.
In a 12-month RCT of Crohn's disease patients (43 per group), vitamin K1 at 1,000 μg daily suppressed undercarboxylated osteocalcin by 81%. Hip fracture patients had significantly lower serum vitamin K1 than controls (case-control study, n=116 cases, 73 controls), with an adjusted odds ratio of 0.07 (95% CI 0.02-0.32) per ng/ml increase—a protective association, though observational in nature.
Joint Health & Cartilage Protection
Evidence Tier: Tier 3 (Probable Association)
Vitamin K1 shows a probable protective association with joint health based on observational studies linking sufficient vitamin K status to better knee osteoarthritis outcomes. Subclinical vitamin K deficiency was associated with a 1.56-fold increased risk of incident radiographic knee osteoarthritis and a 2.39-fold increased risk of cartilage lesions (n=1,180, prospective observational study).
In another observational study (n=791), participants with very low plasma phylloquinone (less than 0.2 nM) were 1.7 times more likely to have cartilage damage progression and 2.6 times more likely to have meniscus damage progression after three years compared to those with sufficient K1 levels.
These associations suggest that maintaining adequate vitamin K1 status may protect joint cartilage, but RCT evidence for direct efficacy is weak and inconsistent.
Anti-Inflammatory Effects
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows potential anti-inflammatory mechanisms, but clinical efficacy for reducing inflammation is not proven. Two RCTs in rheumatoid arthritis patients found inconsistent results:
- In one RCT (n=58), vitamin K1 at 10 mg daily for eight weeks reduced IL-6 by 27% (p=0.006) unadjusted, but this difference was not significant after adjusting for confounders.
- In another RCT (n=64), vitamin K1 at 10 mg daily for eight weeks reduced rheumatoid factor (p=0.041) within-group, but there was no significant difference between groups after adjusting for confounders.
Cardiovascular & Heart Health
Evidence Tier: Tier 3 (Probable Association)
Vitamin K1 shows probable benefits for heart health, particularly in reducing cardiovascular calcification progression and lowering aortic stenosis risk. In a large observational study of 55,545 Danish participants over 21.5 years, higher dietary vitamin K1 intake was associated with 23% lower aortic stenosis risk (HR 0.77, 95% CI 0.63-0.94) and 27% lower risk of aortic stenosis with complications (HR 0.73, 95% CI 0.56-0.95).
In another observational study of 53,372 Danish participants over 21 years, higher dietary vitamin K1 intake was associated with 21% lower atherosclerotic cardiovascular disease hospitalization risk (HR 0.79, 95% CI 0.74-0.84).
However, evidence from general population RCTs is limited and inconsistent regarding most cardiovascular outcomes.
Liver Health
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows promise for preventing coagulation disorders and reducing bleeding risk in specific liver disease contexts. In intrahepatic cholestasis of pregnancy, vitamin K1 deficiency was present in 52.3% of patients versus 2.3% of controls, and postpartum blood loss was higher in the affected group (351±104 mL vs 297±87 mL, p=0.037).
In cirrhotic patients receiving cefoperazone/sulbactam, vitamin K1 supplementation reduced the risk of PT prolongation (OR 0.211, 95% CI 0.047-0.678) and coagulation disorders (OR 0.257, 95% CI 0.126-0.499) compared to the non-supplemented group.
Cognitive Function
Evidence Tier: Tier 3 (Probable Association)
Vitamin K1 shows a probable association with better cognitive function in older adults based on observational studies, but no randomized controlled trials have tested whether supplementation actually improves cognition.
In 5,533 older adults, the highest tertile of 2-year increase in dietary vitamin K intake (median 194.4 μg daily) was associated with lower risk of Mini-Mental State Examination (MMSE) score ≤24 (OR 0.53, 95% CI 0.35-0.79, p=0.002) compared to decreased intake. In 320 cognitively normal older adults (age 70-85), higher serum phylloquinone was associated with better verbal episodic memory on delayed free recall tests (β=0.47, p<0.05 for all three recall measures).
Longevity & Mortality
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows plausible but unproven benefits for longevity through mechanisms related to cardiovascular health, bone density, and physical function. Circulating phylloquinone less than 0.5 nmol/L was associated with 19% higher all-cause mortality risk compared to greater than 1.0 nmol/L over 13 years in 3,891 adults (meta-analysis).
Higher dietary K1 intake (median 120 μg daily versus 49 μg daily) was associated with 26% lower risk of fall-related hospitalization (HR 0.74, 95% CI 0.59-0.93) over 14.5 years in 1,347 older women.
Immune Support
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows immunomodulatory potential in preliminary studies, but human evidence for immune benefits is sparse and inconsistent. In one RCT (n=64 women with rheumatoid arthritis), rheumatoid factor decreased significantly with vitamin K1 (10 mg daily for eight weeks, p=0.041), but this effect was not significant after adjusting for confounders.
A meta-analysis of 13 trials found vitamin K supplementation reduced C-reactive protein (p=0.01) and improved insulin sensitivity index (p<0.001), but had no significant effect on interleukin-6, a key inflammatory cytokine.
Muscle Growth & Athletic Performance
Evidence Tier: Tier 1 (No Proven Effect)
Vitamin K1 has not been demonstrated to promote muscle growth in humans or improve athletic performance. One RCT found it had no effect on bone loss in female endurance athletes: femoral neck bone density decreased similarly in amenorrheic (-6.5% ± 4.0%), eumenorrheic (-3.2% ± 4.1%), and estrogen-supplemented athletes (-3.9% ± 3.1%) regardless of K1 supplementation over two years (n=115).
In animal models, vitamin K1 supplementation reduced tibialis anterior muscle expression of MuRF-1 and MAFbx in LPS-induced inflammation, suggesting possible anti-catabolic effects in sepsis—but this has not been tested in humans.
Sleep
Evidence Tier: Tier 1 (No Evidence)
Vitamin K1 has not been studied for sleep effects in humans. Available literature only examines diurnal rhythms in vitamin K metabolism and absorption, describing when vitamin K is absorbed and processed throughout the day, but provides no evidence that vitamin K1 improves sleep quality, duration, or any sleep outcome.
Skin & Hair Health
Evidence Tier: Tier 2 (Suggestive)
Vitamin K1 shows promise for improving acneiform skin reactions related to EGFR inhibitor therapy in women. In a double-blind RCT, topical vitamin K1 cream (Reconval K1) significantly reduced acneiform skin reactions in women on cetuximab (EGFR inhibitor) versus placebo, though men showed no benefit.
In another double-blind RCT, topical 5% vitamin K cream performed comparably to 20% arnica for laser-induced bruise resolution over two weeks and was superior to placebo. However, evidence for vitamin K's effects on general skin or hair health is limited.
Gut Health
Evidence Tier: Tier 1 (No Proven Effect)
Vitamin K1 has not been demonstrated to improve gut health outcomes when supplemented. While vitamin K1 is involved in maintaining gut microbiota composition and may be produced by intestinal bacteria, no studies prove it actively improves gut health outcomes. In an RCT (n=80), fecal menaquinone concentrations varied widely (64-5,358 nmol daily) and partitioned individuals into two distinct groups based on microbiota composition; whole grain diet decreased fecal menaquinones versus refined grain diet.