Vitamin K for Athletes: Bone Health, Blood Clotting, and Cardiovascular Protection

Published: Nutrition & Micronutrients Guide

If you're serious about bone health and preventing stress fractures, you need to know about vitamin K. While most athletes focus on calcium and vitamin D, vitamin K is the missing piece that actually directs calcium to your bones instead of your arteries. Here's what makes this fat-soluble vitamin essential for training, recovery, and long-term health—and why K2 might be even more important than K1.

Understanding Vitamin K

Vitamin K is a fat-soluble vitamin essential for blood clotting, bone metabolism, cardiovascular health, and calcium regulation. It exists in two primary forms: vitamin K1 (phylloquinone), found predominantly in green leafy vegetables, and vitamin K2 (menaquinones), found in fermented foods, animal products, and produced by gut bacteria. While both forms support blood clotting, vitamin K2 has unique benefits for bone and cardiovascular health by directing calcium to bones and teeth while preventing arterial calcification.

Despite being essential, vitamin K deficiency is rare in healthy adults but can occur in newborns (leading to vitamin K injections at birth), individuals with fat malabsorption disorders, and those taking certain medications. Adequate vitamin K intake is particularly important for athletes and active individuals due to its roles in bone health, reducing fracture risk, and supporting overall skeletal integrity under training stress.

🔍 Find Vitamin K-Rich Foods with FitnessRec

Use FitnessRec's advanced nutrient search to discover foods highest in vitamin K. Simply search by "Vitamin K" to instantly see which foods provide this critical nutrient for bone health, blood clotting, and cardiovascular protection.

Track your vitamin K intake to ensure optimal bone density and cardiovascular health alongside your fitness goals.

Vitamin K1 vs K2: Key Differences

Comparing Vitamin K Forms:

Property Vitamin K1 (Phylloquinone) Vitamin K2 (Menaquinones)
Primary Sources Green leafy vegetables Fermented foods, animal products, gut bacteria
Bioavailability Lower (~10-15%) Higher (~50-80%)
Half-Life Short (hours) Longer (days)
Blood Clotting Primary role Also supports
Bone Health Moderate Superior
Cardiovascular Minimal direct effect Strong (prevents arterial calcification)

Vitamin K2 actually exists in several subtypes (MK-4, MK-7, MK-8, MK-9, etc.), with MK-4 and MK-7 being the most studied. MK-7 has the longest half-life and may be the most beneficial K2 form for bone and cardiovascular health.

Essential Health Benefits

1. Blood Clotting (Coagulation)

Vitamin K's original discovered function is activating clotting factors in the blood:

  • Activates Clotting Proteins: Required for carboxylation of factors II, VII, IX, and X
  • Prevents Hemorrhage: Deficiency causes uncontrolled bleeding
  • K1 Primary Role: Vitamin K1 is the main form used for coagulation in the liver
  • Newborn Deficiency Risk: Babies born with low K stores; injections prevent bleeding
  • Warfarin Interaction: Blood thinners like warfarin work by blocking vitamin K

2. Bone Health and Fracture Prevention

Vitamin K, especially K2, is critical for bone metabolism and strength:

Bone Health Mechanisms:

  • Activates Osteocalcin: Vitamin K carboxylates osteocalcin, a protein that binds calcium to bone matrix
  • Increases Bone Density: Higher K2 intake associated with greater bone mineral density
  • Reduces Fracture Risk: Studies show 60-80% reduction in fracture risk with adequate K2
  • K2 Superior: MK-7 form shows strongest bone benefits in research
  • Works with Vitamin D: Synergistic relationship—D increases calcium absorption, K2 directs it to bones
  • Critical for Athletes: Training stress increases bone turnover; adequate K supports bone adaptation

📊 What Research Shows

Multiple studies from Maastricht University and the University of Wisconsin have demonstrated that vitamin K2 supplementation significantly improves bone mineral density and reduces fracture risk in postmenopausal women by up to 60-80%. Research from Tufts University found that athletes with higher vitamin K intake showed better bone adaptation to training stress and lower incidence of stress fractures.

Practical takeaway: Adequate vitamin K2 intake is essential for athletes engaged in high-impact training to prevent stress fractures and optimize bone strength.

3. Cardiovascular Health (K2 Specific)

Vitamin K2 prevents arterial calcification—the buildup of calcium in blood vessel walls:

Cardiovascular Mechanisms:

  • Activates Matrix Gla Protein (MGP): K2 activates MGP, which prevents calcium from depositing in arteries
  • Reduces Arterial Stiffness: Prevents calcification that hardens arteries and increases blood pressure
  • Lowers Cardiovascular Risk: The Rotterdam Study showed 50% lower heart disease risk with high K2 intake
  • Reverses Calcification: Some evidence suggests K2 can reverse existing arterial calcium deposits
  • Directs Calcium Properly: Ensures calcium goes to bones/teeth, not arteries

4. Dental Health

Vitamin K2 activates osteocalcin in teeth, supporting enamel strength and dentin formation. Adequate K2 may reduce cavities and support overall dental health.

5. Potential Anticancer Effects

Emerging research suggests vitamin K2 may have protective effects against certain cancers, particularly liver and prostate cancer. Mechanisms are still being studied but may involve cell cycle regulation and apoptosis induction.

Why Vitamin K Matters for Athletes

Research from the American College of Sports Medicine and International Olympic Committee emphasizes that bone health is fundamental for athletic longevity. Vitamin K is particularly important for athletes due to bone stress from training:

Athletic Considerations:

  • Bone Health Critical: Weight-bearing exercise increases bone turnover; vitamin K supports proper bone formation
  • Stress Fracture Prevention: Adequate K2 may reduce risk of stress fractures in runners and endurance athletes
  • Inflammation Reduction: Some evidence suggests vitamin K has anti-inflammatory properties
  • Cardiovascular Support: Long-term heart health for endurance athletes through arterial calcium regulation
  • Optimal Intake: Athletes should aim for 150-200 mcg total vitamin K, including dedicated K2 sources

Recommended Intake and Deficiency

Adequate Intake (AI) Levels:

  • Adult men (19+ years): 120 mcg/day
  • Adult women (19+ years): 90 mcg/day
  • Pregnancy and lactation: 90 mcg/day
  • Athletes: May benefit from higher intake (150-200 mcg) due to bone stress

Important Note: These recommendations are based primarily on vitamin K1 requirements for blood clotting. Some experts suggest additional vitamin K2 intake (100-200 mcg/day) for optimal bone and cardiovascular health, beyond what's needed for coagulation.

Deficiency Symptoms

  • Easy Bruising: Bleeding under the skin from minor impacts
  • Prolonged Bleeding: Cuts take longer to stop bleeding
  • Heavy Menstrual Bleeding: In women
  • Blood in Urine or Stool: Gastrointestinal or urinary bleeding
  • Nose Bleeds: Frequent or hard-to-stop epistaxis
  • Weakened Bones (Subclinical): Inadequate osteocalcin activation over time
  • Arterial Calcification (K2 Deficiency): Long-term low K2 increases cardiovascular risk

Best Food Sources

Vitamin K1 Sources

Excellent K1 Sources (per 100g):

  • Kale (cooked): 817 mcg (681% DV)
  • Spinach (cooked): 493 mcg (411% DV)
  • Collard greens (cooked): 623 mcg (519% DV)
  • Turnip greens (cooked): 368 mcg (307% DV)
  • Broccoli (cooked): 141 mcg (118% DV)
  • Brussels sprouts (cooked): 194 mcg (162% DV)
  • Parsley (fresh): 1640 mcg (1367% DV)
  • Swiss chard (cooked): 327 mcg (273% DV)
  • Asparagus (cooked): 60 mcg (50% DV)

Vitamin K2 Sources

Excellent K2 Sources (per 100g):

  • Natto (fermented soybeans): 1000+ mcg MK-7 (richest source by far)
  • Goose liver pâté: 369 mcg
  • Hard cheeses (Gouda, Edam): 50-76 mcg MK-4 and MK-9
  • Soft cheeses (Brie, blue cheese): 30-50 mcg
  • Egg yolk: 15-32 mcg MK-4 (varies with hen's diet)
  • Chicken (dark meat): 8-10 mcg MK-4
  • Butter (grass-fed): 15 mcg MK-4
  • Liver (beef, chicken): 6-10 mcg
  • Sauerkraut: 2-5 mcg MK-7

Note: Natto is exceptionally rich in K2-MK7 but is an acquired taste. Cheese and egg yolks from grass-fed/pasture-raised animals contain significantly more K2 than conventional products.

Practical Recommendations for Athletes

  • Daily Greens: 1-2 cups cooked greens (kale, spinach, collards) provides ample K1
  • Include K2 Sources: Cheese, egg yolks, or fermented foods for bone and cardiovascular benefits
  • Grass-Fed When Possible: Higher K2 content in dairy and eggs from pasture-raised animals
  • Consider K2 Supplement: 100-200 mcg MK-7 if not consuming K2-rich foods regularly
  • Pair with Vitamin D: Synergistic for bone health (D increases absorption, K directs calcium)
  • Take with Fat: Vitamin K is fat-soluble—consume with dietary fat for absorption

Vitamin K2 Supplementation

✅ K2 Supplementation Can Be Beneficial

Unlike K1 (easily obtained from greens), K2 is harder to get in sufficient amounts from diet alone:

  • MK-7 Preferred: Longest half-life (2-3 days); most effective for bone and cardiovascular health
  • Typical Dose: 100-200 mcg/day MK-7
  • Bone Health: Particularly beneficial for those at fracture risk or with osteopenia
  • Cardiovascular Protection: May reverse arterial calcification over time
  • Safe Profile: No known toxicity; no upper limit established
  • Combine with D3: Many supplements pair K2 with vitamin D for synergistic benefits

Best Practice: If supplementing vitamin D (especially high doses >2000 IU), include K2 to ensure calcium is directed to bones, not arteries.

Important Drug Interactions

⚠️ Warfarin and Blood Thinner Caution

If taking warfarin (Coumadin) or similar blood thinners:

  • Warfarin Blocks Vitamin K: These medications work by inhibiting vitamin K activity
  • Consistency is Key: Don't suddenly increase or decrease vitamin K intake
  • Stable Intake Preferred: Eat consistent amounts of K-rich foods daily
  • Don't Avoid Vitamin K: Modern approach is maintaining consistent intake, not avoiding K
  • Consult Doctor: Before starting K2 supplements if on blood thinners

Note: Newer blood thinners (DOACs like rivaroxaban, apixaban) don't interact with vitamin K.

Absorption and Bioavailability

Optimizing Vitamin K Absorption:

  • Fat-Soluble: Requires dietary fat for absorption (5-10g minimum)
  • Cook Greens with Fat: Sauté spinach/kale in olive oil for better K1 absorption
  • K2 Better Absorbed: K2 has 50-80% bioavailability vs 10-15% for K1
  • Gut Bacteria Production: Intestinal bacteria produce some K2, but contribution to total status is debated
  • Digestive Health Matters: Fat malabsorption (Crohn's, celiac, cystic fibrosis) impairs K absorption

Common Questions About Vitamin K

Do I need to supplement vitamin K?

Most people get adequate vitamin K1 from leafy greens. However, vitamin K2 is harder to obtain from diet alone, especially if you don't eat fermented foods or grass-fed animal products. Athletes at risk for stress fractures or those supplementing high-dose vitamin D may benefit from 100-200 mcg MK-7 supplementation.

How does vitamin K affect my training?

Vitamin K supports bone adaptation to training stress, reducing the risk of stress fractures common in runners and endurance athletes. It also supports cardiovascular health by preventing arterial calcification, which is important for long-term athletic performance and heart health.

Can I get enough vitamin K from food alone?

Yes, if you eat 1-2 cups of cooked leafy greens daily (for K1) and include K2 sources like cheese, egg yolks, natto, or grass-fed butter regularly. However, many athletes find it easier to supplement K2-MK7 (100-200 mcg/day) to ensure optimal bone and cardiovascular health.

Should I take vitamin K with vitamin D?

Yes. Vitamin D increases calcium absorption, while vitamin K2 directs that calcium to bones instead of soft tissues and arteries. If you're supplementing vitamin D (especially >2000 IU daily), adding K2 ensures the calcium goes where it's needed most.

How do I track vitamin K in FitnessRec?

Use FitnessRec's advanced nutrient search to find vitamin K-rich foods ranked by content. The app tracks your daily vitamin K intake automatically when you log meals. You can monitor whether you're meeting the 90-120 mcg daily target and see which foods contribute most to your intake.

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💡 Track Your Vitamin K Intake

Use FitnessRec's advanced nutrient search to find foods highest in vitamin K. Tracking your intake ensures you're meeting needs for blood clotting, bone health, and cardiovascular protection—particularly important for athletes with high bone turnover and long-term cardiovascular health goals.

Bottom Line

Vitamin K is essential for blood clotting, bone health, and cardiovascular function. Vitamin K1 (from green vegetables) primarily supports coagulation and is easy to obtain in adequate amounts. Vitamin K2 (from fermented foods, cheese, egg yolks, and animal products) has unique benefits for bone mineralization and preventing arterial calcification—critical for long-term skeletal and cardiovascular health.

Athletes should prioritize adequate vitamin K intake (150-200 mcg total) through daily greens and K2-rich foods like cheese, eggs, or natto. If supplementing vitamin D, consider adding K2-MK7 (100-200 mcg/day) to ensure calcium is properly directed to bones rather than arteries. Use FitnessRec's advanced search to easily identify and track vitamin K-rich foods, optimizing your intake for performance, bone health, and cardiovascular protection.