Vitamin K

Vitamin K1 · Vitamin K2 · Phylloquinone · Menaquinone · Menaquinone-7 · MK-7 · Vitamin K supplementation

Snapshot

Indications	Contraindications
Vitamin K deficiency bleeding¹ Postmenopausal bone health^{2, 3} Vascular calcification⁴ Malabsorption disorders⁵ Glycemic control^{6, 7} Nocturnal leg cramps⁸ Depressive symptoms⁹	Anticoagulant therapy¹⁰ Soy allergy¹⁰ Pregnancy or nursing¹⁰

Vitamin K is a family of fat-soluble compounds: phylloquinone (K1) from leafy greens and menaquinones (K2) from fermented foods and gut bacteria⁵. It works as a cofactor that activates clotting and bone proteins⁵. Supplementation addresses deficiency bleeding in breastfed infants and in malabsorption⁵. It is also used for postmenopausal bone health and vascular calcification, particularly in chronic kidney disease. Glycemic control, nocturnal leg cramps, and depressive symptoms are studied with thinner support.

Meta-analyses of vitamin K2 trials in postmenopausal women report higher lumbar spine density and better osteocalcin carboxylation, though fracture reduction depended on excluding one heterogeneous trial^{2, 3}. Vascular calcification trials split: one meta-analysis found slower coronary calcification progression, while a systematic review found no consistent effect on calcification or arterial stiffness^{4, 11}. In a 2025 observational comparison, low vitamin K status was associated with higher odds of chronic obstructive pulmonary disease (COPD); no trial has tested whether supplementation changes this. Products supply phylloquinone, phytonadione, or menaquinone-4 and menaquinone-7; see Form comparison⁵.

The most consequential caution is anticoagulant antagonism, since warfarin works by opposing vitamin K.⁵ Per the National Institutes of Health fact sheet, people on these medicines keep intake consistent, because sudden changes alter the anticoagulant effect⁵. United States (US) product labels warn against use with anticoagulants unless a physician directs it¹⁰.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

98 sources, 78 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources