Vitamin K

Vitamin K helps make proteins needed for blood clotting and building bones.

Prothrombin is a vitamin K-dependent protein directly involved with blood clotting. Osteocalcin is another protein that requires vitamin K to produce healthy bone tissue. Vitamin K is found throughout the body including the liver, brain, heart, pancreas, and bone. It is broken down very quickly and excreted in urine or stool. Because of this, it rarely reaches toxic levels in the body even with high intakes, as may sometimes occur with other fat-soluble vitamins. Because vitamin K is fat-soluble, it is best to eat vitamin K foods with some fat to improve absorption. So, drizzle some olive oil or add diced avocado to your favorite leafy green salad!

Antibiotics may decrease vitamin K levels, especially if taken for more than a few weeks. People who have a poor appetite while using long-term antibiotics may be at greater risk for a deficiency, and may benefit from a vitamin K supplement. People who are taking blood-thinners, such as warfarin (Coumadin), should avoid suddenly beginning to eat more or fewer foods containing vitamin K, as this vitamin plays a vital role in blood clotting.

Vitamin K deficiency in adults is rare, but may occur in people taking medications. Newborns are sometimes deficient because vitamin K does not cross the placenta, and breast milk contains a low amount. The limited amount of blood clotting proteins at birth increases the risk of bleeding in infants if they are not given vitamin K supplements.

AI: An “adequate intake” (AI) is used when there is not enough evidence to establish a Recommended Dietary Allowance (RDA). The AI amount is estimated to ensure nutritional adequacy. For adults 19 years and older, the AI for vitamin K is 120 micrograms (mcg) daily for men and 90 mcg for women and for those who are pregnant or lactating.

Some Plant-based Food Sources of Vitamin K

collard greensnatto: fermented soybeans
turnip greens
brussels sprouts
soybean oil
canola oil
Source: Harvard University Nutrition Source