Fat-Soluble, Human, Vitamins

Vitamin K (Phylloquinone)

18
May

Vitamin K, specifically phylloquinone (vitamin K1), is a fat-soluble vitamin essential for blood clotting, bone health, and vascular integrity. It supports immune cells like macrophages and T-cells and indirectly aids gut microbiota such as Bacteroidetes, Bifidobacterium, and Lactobacillus. Sourced primarily from green leafy vegetables, its levels are influenced by diet, gut microbiota, and lifestyle. This article provides a clear, engaging, and scientifically accurate overview of vitamin K (phylloquinone), empowering you to understand its properties, biological importance, and health implications, aligning with prior nutrient discussions.

What Is Vitamin K (Phylloquinone)?

Biological Nature and Classification

  • Composition: Fat-soluble naphthoquinone compound, primarily phylloquinone (vitamin K1, plant-derived) and menaquinones (vitamin K2, bacterial/animal-derived). Phylloquinone is the main dietary form.
  • Classification: Essential micronutrient, critical for post-translational modification of proteins involved in coagulation, bone metabolism, and vascular health.
  • Structure:
    • Phylloquinone: 2-methyl-1,4-naphthoquinone ring with a phytyl side chain, enabling fat solubility and membrane integration.
    • Hydrophobic, requiring bile acids and dietary fat for absorption.
  • Properties: Stored in the liver and adipose tissue (half-life ~1–2 days). Normal serum phylloquinone: 0.2–3.2 nmol/L. Absorbed in the small intestine, transported via chylomicrons. Sourced from diet and partially from gut bacterial synthesis (menaquinones), with function supported by dietary fat and gut microbiota.

Biological Role and Mechanism of Action

How Phylloquinone Functions in the Body

  • Blood Clotting:
    • Acts as a cofactor for gamma-glutamyl carboxylase, carboxylating vitamin K-dependent proteins (e.g., factors II, VII, IX, X, protein C, protein S) to enable calcium binding and clot formation:
Phylloquinone → Carboxylase → Gla-Proteins → Clotting Cascade
  • Bone Health:
    • Carboxylates osteocalcin and matrix Gla-protein (MGP), promoting bone mineralization and inhibiting vascular calcification:
Phylloquinone → Osteocalcin/MGP → Bone Formation + Vascular Protection
  • Immune Function:
    • Indirectly supports immune responses by:
      • Maintaining vascular integrity, aiding macrophage and neutrophil migration.
      • Supporting T-cell function via reduced oxidative stress (synergy with vitamin E).
      • Enhancing gut microbiota (e.g., Bacteroidetes, Lactobacillus) via bile acid metabolism and mucosal health.
Phylloquinone → Vascular/Gut Health → Immune Cells (Macrophages, T-Cells)
  • Anti-Inflammatory Effects:
    • Inhibits NF-κB signaling, reducing pro-inflammatory cytokines (e.g., IL-6) in immune cells like mast cells.
  • Synthesis and Distribution:
    • Absorbed in the small intestine, stored in the liver, and recycled via the vitamin K epoxide cycle.
    • Requires dietary fat (5–10 g/meal) and gut microbiota (e.g., Bacteroidetes produce menaquinones):
Phylloquinone + Fat + Gut Bacteria → Absorption → Carboxylation

Physiological Importance

  • Ensures effective blood clotting, preventing excessive bleeding.
  • Supports bone density and prevents osteoporosis.
  • Maintains vascular health, reducing calcification risk.
  • Indirectly enhances immunity and gut microbiota health.
  • Serves as a marker for nutritional and coagulation status.

Dietary Sources and Influences on Phylloquinone

Natural Sources

  • Dietary Phylloquinone (K1):
    • Green leafy vegetables: Spinach (482 µg/100 g), kale (817 µg/100 g), broccoli (102 µg/100 g).
    • Vegetable oils: Soybean oil (184 µg/100 g), canola oil (71 µg/100 g).
    • Other: Green beans (14 µg/100 g), avocados (21 µg/100 g).
    • Bioavailability: 5–20% (higher with fat, lower in raw vegetables).
  • Menaquinones (K2):
    • Fermented foods (natto: 1000 µg MK-7/100 g), cheese (20–80 µg/100 g), egg yolks (15 µg/100 g).
    • Produced by gut bacteria (e.g., Bacteroidetes, limited absorption).
  • Foods Supporting Phylloquinone Function:
    • Fat-rich foods (avocado, nuts: 5–10 g/100 g) enhance absorption.
    • Fermented foods (yogurt, kefir: 10⁸–10¹⁰ CFU/serving) support gut bacteria producing K2.
    • Calcium-rich foods (dairy, greens: 100–300 mg/100 g) complement bone health.
  • Gut Bacteria Contribution:
    • Bacteroidetes and Lactobacillus produce menaquinones, but dietary phylloquinone is the primary source.

Factors Increasing Phylloquinone Levels

  • Dietary Factors:
    • Adequate intake (90–120 µg/day) from greens or oils maintains serum levels (0.2–3.2 nmol/L).
    • Fat co-consumption (5–10 g/meal) increases absorption by 10–20%.
    • Fermented foods (1–2 servings/day) enhance K2 availability.
  • Lifestyle:
    • Balanced diet with greens (1–2 servings/day) ensures steady intake.
    • Cooking (e.g., steaming spinach) improves bioavailability by 5–10%.

Factors Decreasing Phylloquinone Levels

  • Dietary Factors:
    • Low intake (<30 µg/day) reduces serum phylloquinone (<0.2 nmol/L), impairing clotting and bone health.
    • Low-fat diets (<5 g/meal) or malabsorption (e.g., celiac disease) decrease absorption by 10–20%.
    • Antibiotic use disrupts gut bacteria, reducing K2 synthesis.
  • Lifestyle:
    • Excessive alcohol (>2 drinks/day) impairs liver storage, lowering levels by 5–10%.
    • Smoking increases oxidative stress, potentially affecting vitamin K metabolism.
  • Environmental Factors:
    • Malabsorption disorders (e.g., Crohn’s) or bile duct issues impair uptake.
    • Chronic diseases (e.g., liver disease) reduce storage and recycling.

Bioavailability and Formation

  • Phylloquinone is absorbed in the small intestine, with menaquinones partially contributed by gut bacteria (limited systemic impact).
  • Levels peak with consistent intake and decline in deficiency or malabsorption.
  • Deficiency rare in healthy adults (<0.5% prevalence) but common in newborns or malabsorption conditions.

Health Benefits and Potential Risks

Supported Health Benefits

  • Blood Clotting:
    • Ensures rapid clot formation, preventing hemorrhage (e.g., 20–30% reduced bleeding risk with adequate intake).
  • Bone Health:
    • Promotes osteocalcin carboxylation, reducing fracture risk (e.g., 10–15% lower in high K1 intake).
  • Vascular Health:
    • Inhibits arterial calcification via MGP, lowering cardiovascular risk (e.g., 5–10% reduced with adequate K1/K2).
  • Immune Support:
    • Indirectly enhances macrophage and T-cell function via vascular and gut health.
    • Supports gut microbiota (e.g., Bifidobacterium), maintaining mucosal immunity.
  • Anti-Inflammatory Effects:
    • Reduces inflammation markers (e.g., 5–10% lower IL-6 with high K1 intake).
  • Nutrient Synergy:
    • Works with calcium (1000–1200 mg/day), magnesium (300–400 mg/day), vitamin D (15–20 µg/day), and omega-3s (1–2 g/day); complements vitamin E for antioxidant effects.

Health Risks

  • Excessive Intake:
    • Rare, as no upper limit (UL) is set; high doses (>10,000 µg/day from supplements) may cause:
      • Mild gastrointestinal upset (e.g., <1% prevalence).
      • Interference with anticoagulant therapy (e.g., warfarin).
    • Causes: Overuse of K1/K2 supplements.
  • Deficiency:
    • <30 µg/day leads to:
      • Bleeding disorders (e.g., prolonged clotting time, <0.5% prevalence in adults).
      • Increased fracture risk (e.g., 10–15% higher in deficient individuals).
      • Vascular calcification (e.g., 5–10% increased risk).
    • Causes: Low intake, malabsorption, or antibiotic overuse.
  • Allergic Reactions:
    • Rare, but possible with supplements (e.g., to fillers in capsules).
  • Rare Disorders:
    • Vitamin K deficiency bleeding in newborns (0.5–1% without prophylaxis).
    • Deficiency-related osteopenia (<0.1% prevalence in malabsorption).

Recommended Management and Guidelines

Recommended Intake

  • Dietary Reference Intakes (NIH, 2025):
    • Adults: 90 µg/day (women), 120 µg/day (men).
    • Pregnancy/Lactation: 90 µg/day.
    • No Upper Limit (UL) due to low toxicity risk.
  • Typical Levels:
    • Serum phylloquinone: 0.2–3.2 nmol/L; deficiency <0.2 nmol/L; toxicity extremely rare.

Management Strategies

  • Dietary Support:
    • Consume phylloquinone-rich foods (spinach: 482 µg/100 g, kale: 817 µg/100 g, broccoli: 102 µg/100 g).
    • Pair with fat-rich foods (avocado, olive oil: 5–10 g/100 g) to enhance absorption.
    • Include fermented foods (natto, cheese: 20–1000 µg K2/100 g) for K2.
    • Support gut health with prebiotics (5–10 g/day, e.g., onions) for Bacteroidetes and Lactobacillus.
  • Lifestyle:
    • Eat a balanced diet with greens (1–2 servings/day) and fermented foods.
    • Cook greens lightly (e.g., steaming) to improve bioavailability.
    • Avoid excessive alcohol (>2 drinks/day) and quit smoking to protect metabolism.
  • Supplements:
    • Vitamin K1 supplements (50–100 µg/day) for deficiency or malabsorption; K2 (MK-7, 100–200 µg/day) for bone/vascular health.
    • Combine with vitamin D (15–20 µg/day) and calcium (1000–1200 mg/day) for bone health.
    • Consult a doctor before supplements, especially with anticoagulants (e.g., warfarin) or liver disease.
  • Usage Notes:
    • Monitor intake in low-vegetable diets, antibiotic use, or malabsorption conditions.
    • Seek medical advice for bleeding, bone pain, or signs of deficiency (e.g., easy bruising).

Safety, Interactions, and Side Effects

Safety Profile

  • Normal Intake: Safe and essential at 90–120 µg/day.
  • Excess: Rare, with minimal toxicity risk.
  • Deficiency: Impairs clotting and bone health, addressable with diet/supplements.

Possible Interactions

  • Medications:
    • Anticoagulants (e.g., warfarin): Vitamin K reduces efficacy; maintain consistent intake.
    • Antibiotics: Reduce gut K2 synthesis; ensure dietary K1.
    • Orlistat: Reduces fat absorption, lowering K1 uptake.
  • Nutrients:
    • Vitamin D (15–20 µg/day), calcium (1000–1200 mg/day), and magnesium (300–400 mg/day) enhance bone health.
    • Omega-3s (1–2 g/day) and vitamin E (15 mg/day) complement vascular/immunity effects.
    • High-dose vitamin E (>400 IU/day) may interfere with vitamin K clotting function.
  • Medical Conditions:
    • Safe for most; monitor in liver disease, malabsorption (e.g., Crohn’s), or anticoagulant therapy.
    • Deficiency risk in newborns, malabsorption, or low-vegetable diets.

Contraindications

  • Avoid high-dose supplements in:
    • Anticoagulant Therapy: Risk of reduced drug efficacy.
    • Allergies: To supplement fillers (e.g., gelatin).
  • Consult a doctor before supplements in liver disease or bleeding disorders.

Fun Fact

Did you know phylloquinone is like your body’s clotting maestro? A serving of spinach orchestrates your blood clotting and bone health while supporting gut bacteria like Bacteroidetes for a healthy rhythm!

Empowering Your Health Choices

Vitamin K (phylloquinone), your clotting and bone health champion, ensures coagulation, strengthens bones, and supports gut microbiota like Lactobacillus. Maintain levels with phylloquinone-rich foods (90–120 µg/day from spinach, kale, broccoli) and fermented foods (natto, cheese for K2). Pair with fats (avocado, oils), vitamin D (15–20 µg/day), and calcium (1000–1200 mg/day). Avoid excessive alcohol, quit smoking, and cook greens lightly to optimize its role. Consult a healthcare provider for bleeding, bone issues, or anticoagulant concerns. Nourish wisely with phylloquinone support for a vibrant, healthy you!