Vitamin

Vitamin K

Phylloquinone (K1) / Menaquinone (K2)

Evidence TierAWADA NOT PROHIBITED

tuneTypical Dose

90-120 mcg K1, 100-200 mcg K2 MK-7

watchEffect Window

Hours for coagulation; months for bone/vascular outcomes.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

Vitamin K is required to activate clotting factors and certain bone-related proteins. It is used to prevent deficiency-related bleeding and to support bone protein activation and calcium handling.

Adequate vitamin K prevents bleeding due to impaired clotting factor activation, with clear relevance in newborn prophylaxis and malabsorption contexts. It activates osteocalcin and other proteins involved in bone mineralization pathways. Minority evidence suggests slowed vascular calcification progression in some studies. Anticoagulant interactions are clinically important, so benefits depend on consistent intake patterns and supervision when on warfarin.

K1 activates clotting factors in the liver. K2 activates osteocalcin (bone) and matrix Gla protein (vascular), directing calcium to bones and away from arteries.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Essential blood coagulation cofactor
  • Rapid warfarin reversal

Secondary Outcomes

  • K2 may reduce arterial calcification
  • K2 supports bone mineral density
  • Prevents hemorrhagic disease of newborn

Safety

Contraindications and Interactions

Contraindications

  • Warfarin/coumadin therapy without physician INR management

Side effects

  • Generally none at supplemental oral doses.
  • Mild GI upset (nausea, abdominal pain, diarrhea).
  • Rare hypersensitivity-type reactions (anaphylactoid/non-IgE reactions, flushing, dyspnea, rash, blood pressure changes, tachycardia, bradycardia), reported mainly with injectable vitamin K.

Interactions

  • Warfarin (direct antagonist)
  • Broad-spectrum antibiotics (may reduce gut K2 production)

Avoid if

  • Warfarin or vitamin K antagonist anticoagulant use without physician management

Evidence

Study-level References

vitamin-k-SRC-001Review
Sourceopen_in_new

Booth SL. "Vitamin K: food composition and dietary intakes." Food Nutr Res. 2012.

Population: General population

Key findings: Comprehensive overview of vitamin K forms, dietary sources, and the distinct physiological roles of K1 (coagulation) and K2 (extra-hepatic functions).

Paper content

Comprehensive overview of vitamin K forms, dietary sources, and the distinct physiological roles of K1 (coagulation) and K2 (extra-hepatic functions).

vitamin-k-SRC-002Randomized controlled trial
Sourceopen_in_new

Knapen MH, Braam LA, Drummen NE, et al. "Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women." Thromb Haemost. 2015.

Population: Healthy postmenopausal women

Key findings: 180 mcg MK-7 daily for 3 years significantly improved arterial stiffness compared to placebo, particularly in women with higher baseline stiffness.

Paper content

180 mcg MK-7 daily for 3 years significantly improved arterial stiffness compared to placebo, particularly in women with higher baseline stiffness.

vitamin-k-SRC-003Systematic review and meta-analysis
Sourceopen_in_new

Cockayne S, Adamson J, Lanham-New S, et al. "Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials." Arch Intern Med. 2006.

Population: Primarily Japanese postmenopausal women

Key findings: Vitamin K2 supplementation (predominantly MK-4 at 45 mg) was associated with reduced fracture risk; however, most evidence comes from Japanese populations and may not generalize.

Paper content

Vitamin K2 supplementation (predominantly MK-4 at 45 mg) was associated with reduced fracture risk; however, most evidence comes from Japanese populations and may not generalize.

vitamin-k-SRC-004Double-blind randomized controlled trial.
Sourceopen_in_new

Lithgow H, Johnston L, Ho F, et al. The Effects of Vitamin K2 on Recovery from Muscle-Damaging Resistance Exercise in Young and Older Adults: The TAKEOVER Randomized Controlled Trial. Med Sci Sports Exerc. 2026;58(4):683-694. doi:10.1249/MSS.0000000000003901. PMID:41843412.

Population: Young adults aged 18-40 and older adults aged 65 and over.

Dose protocol: MK-7 240 mcg daily for 12 weeks before eccentric exercise in 71 young and older adults.

Key findings: No overall effect on muscle recovery. Age-specific interactions in older adults for creatine kinase and IL-6 suggest K2 may selectively modulate post-exercise inflammation in aging populations.

Notes: Important null result for general exercise recovery, with exploratory age-specific signals.

Paper content

This double-blind RCT tested 12 weeks of MK-7 (240 mcg/day) supplementation on recovery from muscle-damaging eccentric exercise in 71 young and older adults. Vitamin K2 did not improve overall muscle strength recovery, physical function, soreness, or inflammation after exercise. However, age-specific interactions were observed in older adults for creatine kinase, IL-6, and electromechanical delay, suggesting K2 may have selective recovery benefits in aging muscle that warrant further investigation.

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