In this article, we describe:
- the major purposes of this specific nutrient in the human body,
- its experimentally confirmed health uses,
- conventional ways to estimate nutrient status,
- nutrient’s toxicities and deficiencies,
- experimentally confirmed and approved levels of the nutrient intake for different demographics,
- dietary sources of the nutrient.
“Vitamin K” is the generic name for a family of fat-soluble compounds with a common chemical structure. These compounds include phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2).
Phylloquinone is present primarily in green leafy vegetables and is the main dietary form of vitamin K. Menaquinones, which are predominantly of bacterial origin, are present in modest amounts in various animal-based and fermented foods. Almost all menaquinones are also produced by bacteria in the human gut.
Vitamin K functions as a coenzyme for vitamin K-dependent carboxylase, an enzyme required for the synthesis of proteins involved in hemostasis (blood clotting) and bone metabolism. For this reason, individuals who are taking anticoagulants need to maintain consistent vitamin K intakes.
Like dietary lipids and other fat-soluble vitamins, ingested vitamin K is absorbed by enterocytes of the small intestine and repackaged into very low-density lipoproteins (very small amounts of vitamin K circulate in the blood). Vitamin K is present in the liver and other body tissues, including the brain, heart, pancreas, and bone, but is rapidly metabolized and excreted. Research also indicates that substantial quantities of long-chain menaquinones are present in the large bowel.
In most cases, vitamin K status is not routinely assessed, except in individuals who take anticoagulants or have bleeding disorders. The only clinically significant indicator of vitamin K status is prothrombin time (the time it takes for blood to clot), and ordinary changes in vitamin K intakes have rarely been shown to alter prothrombin time. In healthy people, fasting concentrations of phylloquinone in plasma have been reported to range from 0.29 to 2.64 nmol/L. However, it is not clear whether this measure can be used to quantitatively assess vitamin K status.
People with plasma phylloquinone concentrations slightly below the normal range have no clinical indications of vitamin K deficiency, possibly because plasma phylloquinone concentrations do not measure the contribution of menaquinones from the diet and the large bowel. No data on normal ranges of menaquinones are available. Vitamin K deficiency can occur during the first few weeks of infancy due to low placental transfer of phylloquinone, low clotting factor levels, and low vitamin K content of breast milk. Clinically significant vitamin K deficiency in adults is very rare and is usually limited to people with malabsorption disorders or those taking drugs that interfere with vitamin K metabolism. In healthy people consuming a varied diet, achieving a vitamin K intake low enough to alter standard clinical measures of blood coagulation is almost impossible. No adverse effects associated with vitamin K consumption from food or supplements have been reported in humans or animals.
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Adequate Values (AI) for Vitamin K
|Birth to 6 months||2.0 mcg||2.0 mcg|
|7–12 months||2.5 mcg||2.5 mcg|
|1–3 years||30 mcg||30 mcg|
|4–8 years||55 mcg||55 mcg|
|9–13 years||60 mcg||60 mcg|
|14–18 years||75 mcg||75 mcg||75 mcg||75 mcg|
|19+ years||120 mcg||90 mcg||90 mcg||90 mcg|
Food Sources of Vitamin K
Food sources of phylloquinone include vegetables, especially green leafy vegetables, vegetable oils, and some fruits. Meat, dairy foods, and eggs contain low levels of phylloquinone but modest amounts of menaquinones. Natto (a traditional Japanese food made from fermented soybeans) has high amounts of menaquinones. Other fermented foods, such as cheese, also contain menaquinones. However, the forms and amounts of vitamin K in these foods likely vary depending on the bacterial strains used to make the foods and their fermentation conditions. Poultry and pork products contain menaquinones if menadione is added to the animal feed.
The most common dietary sources of vitamin K are spinach; broccoli; iceberg lettuce; and fats and oils, particularly soybean and canola oil. Few foods are fortified with vitamin K.
Consuming vegetables at the same time as some fat improves phylloquinone absorption from the vegetables, but the amount absorbed is still lower than that from oils.
The table below shows phylloquinone content, except when otherwise indicated, because food composition data for menaquinones are limited.
Selected Food Sources of Vitamin K
|Natto, 3 ounces (as menaquinone)||850||708|
|Boiled collard greens, ½ cup||530||442|
|Boiled turnip greens, ½ cup||426||355|
|Raw spinach, 1 cup||145||121|
|Raw kale, 1 cup||113||94|
|Boiled broccoli, ½ cup||110||92|
|Roasted soybeans, ½ cup||43||36|
|Carrot juice, ¾ cup||28||23|
|Soybean oil, 1 tablespoon||25||21|
|Cooked edamame, ½ cup||21||18|
|Canned pumpkin, ½ cup||20||17|
|Pomegranate juice, ¾ cup||19||16|
|Raw okra, ½ cup||16||13|
|Salad dressing Caesar, 1 tablespoon||15||13|
|Dried pine nuts, 1 ounce||15||13|
|Blueberries, ½ cup||14||12|
|Iceberg lettuce, 1 cup||14||12|
|Rotisserie chicken breast, 3 ounces (as menaquinone)||13||11|
|Grapes, ½ cup||11||9|
|Vegetable juice cocktail, ¾ cup||10||8|
|Canola oil, 1 tablespoon||10||8|
|Dry roasted cashews, 1 ounce||10||8|
|Raw carrots, 1 medium||8||7|
|Olive oil, 1 tablespoon||8||7|
|Broiled ground beef, 3 ounces (as menaquinone)||6||5|
|Dried figs, ¼ cup||6||5|
|Braised chicken liver, 3 ounces (as menaquinone)||6||5|
|Cooked ham, 3 ounces (as menaquinone)||4||3|
|Cheddar cheese, 1½ ounces (as menaquinone)||4||3|
|Mixed nuts, dry roasted, 1 ounce||4||3|
|Hard-boiled egg, 1 large (as menaquinone)||4||3|
|Mozzarella cheese, 1½ ounces (as menaquinone)||2||2|
|Milk, 2%, 1 cup (as menaquinone)||1||1|
|Cooked sockeye salmon, 3 ounces (as menaquinone)||0.3||0|
|Cooked shrimp, 3 ounces (as menaquinone)||0.3||0|
- *DV = Daily Value.
- The DV for vitamin K used for the values in the table above is 120 mcg for adults and children age 4 years and older.
- Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
- Elson Haas. “Staying Healthy with Nutrition”
- U.S. Department of Health & Human Services: https://ods.od.nih.gov/factsheets/vitaminK-HealthProfessional/