Vitamin K is a fat-soluble vitamin that performs a variety of functions in the body. It’s particularly significant for blood coagulation and bone strengthening.
In this article, you’ll learn all the essential details about vitamin K foods (the primary natural sources of this vitamin), recommended dietary intake of vitamin K, and vitamin K deficiency.
Vitamin K—Definition and Forms
Vitamin K is one of the four fat-soluble vitamins found in vitamin-K-rich foods or dietary supplements. Vitamin K comes in two forms—vitamin K1 (phylloquinone) or vitamin K2 (menaquinones).
Phylloquinone is the main dietary form of vitamin K found mainly in green leafy vegetables high in vitamin K (kale, mustard greens, swiss chard, etc.). On the other hand, menaquinones are present in fermented plant-based foods and animal-based foods.
Menaquinones are of bacterial nature and are characterized by unsaturated isoprenyl side chains. The number of chains may vary from four to thirteen. They also get named according to the number of the chains they feature (MK-4, MK-7, MK-9, etc.).
A Brief History of Vitamin K
Vitamin K was discovered in 1929 by Henrik Dan, a Danish scientist. He found this vitamin by recreating an experiment, initially performed by three Ontario Agricultural College scientists (McFarlan, Graham, and Richardson), in which chloroform was used to remove all the fat from chick feeds.
Chicks fed with fat-depleted feed began hemorrhaging and bleeding from tag sites soon after. These were classic symptoms of vitamin K deficiency, unknown to the scientists at the time.
Dam noticed that even after reintroducing purified cholesterol into the chicks’ diet, they still wouldn’t properly recover. This was because, along with cholesterol, another substance was unknowingly extracted from the food—a nutrient responsible for blood coagulation.
The newly discovered substance’s name was derived from this particular feature. It was named vitamin K (or Koagulationsvitamin, in German) in the first study published on this nutrient.
However, vitamin K structure and dietary sources of vitamin K remained unknown for years to come. It was only a decade later that Edward Adelbert Doisy of Saint Louis University deciphered its chemical nature and structure.
Four years later, in 1943, Dam and Doisy received the Nobel Prize in Medicine, acknowledging their outstanding work on vitamin K1 and vitamin K2.
Benefits of Vitamin K
Vitamin K is vital for various body functions—from bone health to blood coagulation.
The following section highlights some of the most important details.
Vitamin K can help prevent osteoporosis, as it plays an essential role in the mineralization of bones. It can also improve bone density and reduce the risk of fractures.
Improved memory is also one of the vitamin K benefits. A study examining 320 individuals over 70 years of age associated higher vitamin K levels with better verbal episodic memory.
Studies show that vitamin K helps lower blood pressure by decreasing the deposition of minerals in the walls of blood vessels. Mineral deposition occurs naturally with age and gradually leads to the hardening of the blood vessels.
There’s some evidence that the adequate intake of foods high in vitamin K can reduce the peripheral resistance of the blood vessels, enable blood flow, and slow down this process.
Vitamin K has a significant role in the coagulation cascade. It helps create four out of thirteen proteins needed for blood clotting—clotting factors II, VII, IX, and X.
Vitamin K Food Sources
There are various food sources of vitamin K. Plant-based sources of vitamin K are typically richer in phylloquinone, while animal food sources are abundant in menaquinones.
This traditional Japanese food made with fermented soybeans is one of the best menaquinone sources. A 3-oz serving of this menaquinone-rich dish provides as much as 850 mcg (708% DV) of vitamin K.
When consumed raw, this cabbage-like vitamin K vegetable provides as much as 113 mcg (94% DV) of vitamin K per cup. Boiled kale offers a whopping 493 mcg (411% DV) of phylloquinone.
Another source on our list is cabbage, a vitamin K source of great importance. A cup of chopped raw cabbage provides 67.6 mcg (56% DV) of vitamin K. On the other hand, boiled cabbage offers 81.8 mcg (68% DV) of phylloquinone per cup.
Broccoli also tops the list of vegetables with vitamin K. One cup of chopped raw broccoli contains up to 92.8 mcg (77% DV) of vitamin K. Its vitamin D content increases with cooking and amounts to 162.1 mcg (135% DV) per cup when boiled.
Spinach is one of the top-ranking vitamin K foods. Raw spinach contains the lowest amount of vitamin K, with one cup offering 145 mcg (121% DV) of vitamin K.
In comparison, boiled spinach provides a much higher vitamin K content—889 (741%) mcg per cup.
Though often thrown away and disregarded, turnip greens are an excellent source of vitamin K and various other vitamins and minerals. Half a cup of boiled frozen turnip greens provides 426 mcg (355% DV) of vitamin K.
Sweet Potato Leaves
While sweet potatoes aren’t the richest of vegetables with vitamin K (providing up to 6.12 mcg (5% DV) per cup), sweet potato leaves provide an abundance of this vitamin.
A cup of raw sweet potato leaves contains 106 mcg (88% DV) of vitamin K per cup, while a cup of steamed leaves provides 109 mcg (91% DV).
Mustard greens are also a good source of vitamin K. One cup of raw mustard green contains 144 mcg (120% DV) of vitamin K. On the other hand, cooked mustard greens provide as much as 830 mcg (691% DV) per cup.
There’s a reasonable amount of vitamin K in lettuce. Naturally, the vitamin K content varies among different varieties.
For example, iceberg lettuce contains the lowest phylloquinone levels—17.4 mcg (15% DV) per cup. On the other hand, Romaine lettuce and green leaf lettuce contain 47.9 mcg (40% DV) and 45.4 mcg (38% DV), respectively.
These root vegetables are a good source of vitamin K. One cup of raw carrots offers 16.9 mcg (14% DV) of vitamin K. Boiled carrots have slightly higher vitamin K content, providing up to 19.86 (16% DV) mcg per cup.
Carrot juice is an even better vitamin K source providing 28 mcg (23% DV) in a 3/4 cup.
A cup of raw green beans contains 14.4 mcg (12% DV) of vitamin K while a cup of cooked green beans provides 20 mcg (17% DV).
There’s 36 mcg (30% DV) of vitamin K in peas (one cup, raw peas). On the other hand, boiled peas provide 41.4 mcg (34% DV) of phylloquinone per cup.
Yams offer up to 3.45 mcg (3% DV) of vitamin K per cup.
There’s also some vitamin K in avocado. One cup of raw avocados contains 31.5 mcg (26% DV) of vitamin K. A cup of pureed avocado provides a higher vitamin K content—48.3 mcg (40% DV).
Blueberries rank relatively high on the vitamin K foods list, offering 28.6 mcg (24% DV) of vitamin K per cup.
This dairy product high in probiotics is also a good vitamin K food. One cup offers 9.17 mcg (8% DV) of vitamin K. While it might help you lose weight, low-fat yogurt won’t provide you with astronomical amounts of vitamin K. It contains a meager 2.94 mcg (2% DV) per cup.
Cheddar cheese is one of the moderate menaquinone food sources. One cup of diced cheddar provides 3.7 mcg (3% DV) of vitamin K. One cup of melted cheddar offers 6.83 mcg (6% DV) of this vitamin.
Eggs are excellent vitamin K sources for vegetarians. Scrambled eggs provide up to 8.8 mcg (7% DV) per cup. Hard-boiled eggs are also a good food source of menaquinone, providing 4 mcg (3% DV) of vitamin K per one large egg.
Shrimps are a vitamin K food with moderate vitamin K levels. You can get 38.6 mcg (32% DV) from a 3.5-oz serving of golden fried shrimps.
This popular nutritious fish rich in omega-3s contains meager amounts of vitamin K. One can of pink salmon contains only 2.06 mcg (2% DV) of vitamin K per can.
Chicken is a moderate vitamin K source. A 3-oz serving of chicken rotisserie provides 13 mcg (11% DV) of vitamin K.
Although it’s the third most-consumed meat worldwide, beef is one of the foods low in vitamin K. You can get a meager 0.45 mcg (0.4% DV) of vitamin K from an ounce of corned beef.
Broiled ground beef offers a slightly higher vitamin K content, containing 6 mcg (5% DV) of menaquinone-4 in a 3-oz serving. Broiled steak provides 4.96 mcg (4% DV) of vitamin K per oz.
Vitamin K Absorption
After reaching the stomach, foods rich in vitamin K get broken down and start releasing vitamin K. Vitamin K then gets into the bloodstream by absorption through the jejunum and ileum in the presence of bile and pancreatic juices.
Niemann–Pick C1-Like 1 (NPC1L1), an intestinal membrane protein that mediates cholesterol absorption, plays a vital role in vitamin K1 absorption.
However, various factors can impede vitamin K absorption, potentially leading to deficiency. For example, studies show that ezetimibe, a drug used to treat hypercholesterolemia, may reduce vitamin K1 absorption.
Vitamin K Deficiency
Clinically relevant vitamin K deficiency occurs when prothrombin time significantly increases. In other words, the lack of vitamin K leads to the body’s reduced ability to clot blood, resulting in hemorrhage and bleeding.
The most common vitamin K deficiency symptoms include bleeding, developing tiny blood clots under the nails, bruising, black and bloody stool, etc.
Deficient individuals are also prone to prolonged bleeding as a result of minor accidents. Moreover, since vitamin K is in charge of osteocalcin carboxylation in bones, deficiency may lead to reduced bone mineralization and osteoporosis.
Groups at Risk of Vitamin K Inadequacy
Vitamin K deficiency is rare (virtually impossible) in adults with a balanced diet. Most frequently, it occurs in individuals with malabsorption issues and those taking medications that inhibit the vitamin K metabolism.
These are the groups most at risk of becoming deficient:
Neonates Not Treated With Vitamin K at Birth
Vitamin K deficiency in newborns occurs due to the reduced transport of vitamin K across the placenta. It becomes clinically evident during the first weeks of life when VKDB (vitamin K deficiency bleeding) occurs. VKDB is linked with bleeding from the gastrointestinal tract, skin, nose, umbilicus, etc.
Late VKBD occurs at the age of 2–15 weeks in exclusively breastfed infants due to breastmilk’s low vitamin K content. Late VKBD may lead to sudden intracranial bleeding, often resulting in death.
To decrease the incidence of VKDB, the American Academy of Pediatrics recommends treating all newborns with a single intramuscular dose of vitamin K1 (0.5–1 mg).
People With Malabsorption Disorders
Individuals with celiac disease, Crohn’s disease, ulcerative colitis, cystic fibrosis, and short bowel syndrome usually have difficulty absorbing vitamin K.
Additionally, gastric bypass surgery patients are also susceptible to vitamin K deficiency, despite often not developing characteristic clinical deficiency signs.
Interactions With Medications
Vitamin K may react either inhibitory or stimulatory with different medications. Therefore, it’s advised to discuss your vitamin K status with your doctor and watch your intake of foods with vitamin K if taking therapy discussed below.
Anticoagulant medications such as warfarin (Coumadin®), acenocoumarol, phenprocoumon, and tioclomarol reduce vitamin K action and decrease the number of vitamin K-dependent clotting factors to prevent clotting.
Excessive vitamin K intake can interfere with the effectiveness of such drugs. Since it’s possible that a diet rich in K vitamin could reduce the effect of anticoagulants, here’s a brief list of vitamin K foods to avoid while on Coumadin and related medications:
- Kiwi, etc.
Antibiotics may damage vitamin-K-producing bacteria located in the gut and cause a decrease in vitamin K blood levels. This is especially true of cephalosporin antibiotics like cefoperazone, as such medications also directly inhibit the vitamin K action.
Thus, individuals taking these medications are advised to increase their intake of foods rich in vitamin K.
Bile Acid Sequestrants
Cholesterol-reducing medications like colestipol and cholestyramine can inhibit the absorption of vitamin K and other fat-soluble vitamins.
Recommended Dietary Intake
The following table illustrates the recommended daily intake of vitamin K for different age groups:
|0–6 months||2 mcg||2 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|
Vitamin K Supplements
Taking a good vitamin K supplement is an excellent alternative for those with restricted access to vitamin-K-rich food. Multivitamin tablets typically offer 75% DV of this vitamin.
Supplements may feature several different vitamin K forms. Vitamin K1 is present in the form of phylloquinone or phytonadione (a synthetic form of vitamin K1). Vitamin K2 appears either as MK-4 or MK-7 (which has a long half-life).
Menadione (vitamin K3), a synthetic form of vitamin K, is no longer used in supplements since it was proved harmful to hepatocytes in studies conducted in the 1980s and 1990s.
Vitamin K Toxicity
There’s no evidence that too much vitamin K in the system causes toxicity.
Vitamin K is an essential nutrient vital for blood coagulation and bone strengthening. Vitamin K foods are an excellent source of this nutrient for deficiency patients or individuals on antibiotics and other medications that lower vitamin K blood levels.
Alternatively, people with restricted access to such foods could use a vitamin K shot or supplements to regulate low vitamin K levels and prevent osteoporosis, poor blood coagulation, etc.
What is vitamin K?
Vitamin K is one of the four fat-soluble vitamins found in food high in vitamin K or supplements. It’s responsible primarily for blood coagulation and bone strengthening.
What does vitamin K do to your body?
Vitamin K supports bone health and improves cognitive function and blood coagulation.
What are the side effects of too much vitamin K?
There’s no evidence that excessive vitamin K intake produces harmful side effects.
What are the symptoms of low vitamin K?
Low vitamin K levels can be characterized by excessive bleeding from minor wounds, bruising, heavy periods, blood in the urine and stool, etc.
A varied diet including vitamin K foods is usually enough to maintain vitamin K levels and avoid deficiency.