Vitamin K: K1, K2, Food Sources & Warfarin Safety
VITAMIN K GUIDE
Vitamin K is required for normal blood clotting and also participates in bone-related proteins. K1 and K2 are different forms within the vitamin K family, but marketing claims that K2 acts like a simple “traffic cop” directing calcium away from arteries go beyond what current evidence can establish.
K1 and K2
Vitamin K1 (phylloquinone) is abundant in leafy green vegetables. Vitamin K2 refers to menaquinones found in some fermented and animal foods and also produced by bacteria. Both forms contribute to vitamin K activity, though their food sources and metabolism differ.
Bone Health
Vitamin K is involved in proteins important for bone metabolism. Some studies of vitamin K intake or supplementation have reported bone-related benefits, while others have not. Current evidence does not support treating K2 supplements as a guaranteed way to prevent osteoporosis or fractures.
Heart and Arterial Calcification Claims
Vitamin-K-dependent proteins are involved in vascular biology, and researchers continue to study whether vitamin K status relates to arterial calcification or cardiovascular outcomes. This is an active research area; K2 supplements should not be presented as proven to “keep calcium out of arteries” or prevent heart disease.
Food Sources
- K1: kale, spinach, collards, broccoli, Brussels sprouts, and other leafy greens
- K2: natto and some fermented or animal foods, with amounts varying widely
Most people in the United States obtain adequate vitamin K from food.
Warfarin Safety
Vitamin K can significantly affect warfarin therapy. The goal is generally not to eliminate vitamin-K-rich foods, but to keep intake relatively consistent and follow the anticoagulation team's instructions.
Do not start or stop a vitamin K supplement, or make major sustained changes in vitamin K intake, without discussing it with the clinician managing warfarin therapy.
Other Medication Considerations
Some medications can affect vitamin K absorption or status. Tell your doctor or pharmacist about all supplements and medicines you use so they can review relevant interactions.
Final Takeaway
Vitamin K matters for normal clotting and bone-related biology. Food is the primary source for most people, and K2 supplement claims should be interpreted cautiously. Warfarin users should prioritize consistent intake and professional guidance.
Disclaimer: This content is for general educational purposes only and is not medical advice.