Vitamin K has an excellent safety profile, even at high doses. In fact, the National Academies Food and Nutrition Board did not even designate an upper limit for vitamin K1 or K2. That’s because no adverse effects have been documented from either form of vitamin K in humans or animal models when it’s consumed via food or supplements.
Remember that your daily needs for vitamin K are 90 to 120 mcg depending on your gender. To put this recommendation in perspective, one-half cup of collard greens will deliver over 500 mcg of vitamin K1, and three ounces of nattō pack a vitamin K2 punch at 850 mcg. Supplements can deliver a range of vitamin K1 and K2 doses on top of what you consume from your diet.
While safety is excellent for vitamin K2 (and K1), it’s always prudent to discuss any major diet or supplement changes with your doctor, especially if you have a health condition or are taking any medications.
Anticoagulants and vitamin K are a well known drug-nutrient interaction. For this reason, some patients on anticoagulants think they should limit all sources of vitamin K. This is an unfortunate mistake that can create a vitamin K gap or deficiency.
When taking blood-thinning medications, the important thing is to keep vitamin K inputs stable (not low). If a patient on blood thinners wants to incorporate vitamin K-dense foods (healthy foods!) into their diet or take a supplement containing vitamin K1 or K2, they should tell their doctor first. The healthcare practitioner will monitor key blood clotting biomarkers and adjust the medication accordingly.