Vitamin K is a fat-soluble vitamin that plays an important role in blood clotting. In fact, without it our blood would not clot. Its name is derived from the German word “koagulation.” Vitamin K also contributes to skeletal health because it plays a role in bone mineralization. Like vitamin D, vitamin K is one that your body can produce on its own, but usually not in quantities that meet the body’s needs. Bacteria of the lower bowel produce vitamin K and then store it in the liver. However, it has been difficult to determine the contribution of this form of vitamin K to body stores.
The best food sources of vitamin K are leafy green vegetables like spinach, broccoli, eggs, wheat bran, and olive, soy and canola oils. Because vitamin K is a fat-soluble vitamin, its absorption from vegetables is enhanced by the presence of dietary fat: so sauté your spinach in a little olive oil.
Vitamin K deficiency is extremely rare in healthy adults. Cases of deficiency usually only occur in individuals with malabsorption problems, severe liver damage or disease, or those being treated with drugs that interfere with the vitamin’s metabolism. Your health care professional will let you know if you fall into one of these categories. The main symptoms in these cases are that blood doesn’t coagulate normally and you can experience increased bruising.
Infants born in the United States and Canada routinely receive a dose of vitamin K at birth (usually 0.5-1 mg intramuscularly or 2.0 mg orally within 6 hours of birth). This is because infants are usually born with poor vitamin K status and low amounts of clotting factors, thus increasing the risk of bleeding during the first few weeks. In addition, their immature intestines cannot produce vitamin K. Exclusively breastfed infants receive low amounts of vitamin K from human milk.
It’s not likely that you will experience adverse effects from consuming too much vitamin K—but moderation is still the best approach. However, individuals on warfarin therapy—an anticoagulant, or blood-thinning drug—are advised to monitor intake closely and they need to maintain steady vitamin K intake levels. Vitamin K may reduce the effectiveness of this drug. These individuals should maintain their normal dietary and supplementation patterns once an effective dose of the drug has been established. It is generally recommended that these individuals try to consume the recommended intake but avoid large fluctuations in intake.
The following table lists the recommended intake for healthy people based on current scientific information.