vitamin K

Foods Richest in vitamin K

About vitamin K

Basic Description

If you’ve read about vitamins A, B, C, D, and E, you might feel like we’ve missed a few vitamins as we jump over to vitamin K. But there are no vitamins F through J (at least not yet). Vitamin K is named after the German word for blood clotting (koagulation). In fact, this is probably the most common connection that people make with vitamin K—they associate this vitamin with the process of blood clotting. We’ll explain more about this function of vitamin K in our “Role in Health Support” section below. However, it’s important to know that vitamin K makes a variety of unique contributions to our health, and our knowledge about these contributions has been expanding in new and unexpected ways.

There are three basic types of vitamin K. Their common names are K1, K2, and K3.

The K1 form of vitamin K is found in plant foods, and 44 of our WHF are plant foods that serve as excellent, very good, or good sources of vitamin K! Many of our best sources of this vitamin are green vegetables (including 16 excellent sources); this makes good sense since K1 is required for green plants to conduct the process of photosynthesis. The K2 form of vitamin K is made from K1 and K3 by bacteria and other microorganisms. It can also be made in the human body through a conversion process involving K1 and K3.

In plant foods, you won’t find much preformed K2, unless those plant foods have been fermented or otherwise transformed by bacteria or other microorganisms. Certain microorganisms can convert K1 into K2. A great example is Bacillus natto. This bacterium can convert K1 into K2 and it is often used in the production of fermented soy products. In fact, this practice is so common that you will sometimes find the word “natto” being used to refer to these foods. Fermented soyfoods on our WHF list—including tempeh and miso—can contain significant amounts of K2. (And as plant foods, they also naturally contain K1.) Most of our WHF animal foods also contain K2, although the amounts are relatively small and insufficient to qualify them as excellent, very good, or good sources of vitamin K.

A third type of vitamin, found preformed in food but in very small amounts, is menadione, or vitamin K3. We don’t yet have good research on the health role of these small of K3 amounts in food.

Role in Health Support

Blood Clotting

As mentioned in the Description section, vitamin K is perhaps best known for its role in the blood clotting process. When people hear the term “blood clot,” they might sometimes jump to the conclusion that a blood clot is bad. But there are many times when it is very important for our blood to clot. For example, blood clots are necessary to stop bleeding when our skin gets punctured.

Yet at the same time, people are correct when they say that blood clotting can cause problems. For example, if the inside of a blood vessel has become too narrow due to the buildup (over time) of plaque, this plaque can sometimes rupture and our body may form a blood clot in order to seal off the ruptured plaque. However, this blood clot might also end up stopping the flow of blood through the blood vessel since the blood vessel had become overly narrowed from the buildup of plaque.

Regardless of the specific situation, vitamin K is necessary for blood clots to form. The clotting process is very complex, requiring at least 12 proteins to function before the clotting process can be completed. Four of these protein clotting factors require vitamin K for their activity.

Luckily, we rarely see vitamin K deficiency lead to impairment in the clotting process in adults. We see it in newborns because vitamin K does not efficiently cross the placenta to the fetus, and it can take several weeks for the fetus to build up dietary stores. We also occasionally see clotting problems related to vitamin K deficiency in persons with severe liver or gastrointestinal diseases. But vitamin K deficiency basically never causes insufficient clotting disorders in healthy adults.

In contrast to insufficient clotting in healthy adults, we do see vitamin K deficiency becoming involved in unwanted clotting. This process once again involves the activity of multiple vitamin K-dependent enzyme systems, most importantly a system called matrix Gla protein.

It is currently somewhat of an open question how important vitamin K is to the progression of clot formation and heart disease. Researchers have sometimes, but not consistently, been able to correlate low vitamin K intake with increased risk of heart disease.

One problem in interpreting this research, however, is separating out the effect of healthy foods from the nutrients they contain. Even casual readers of this site are probably aware that the same green leafy vegetables that are our richest sources of vitamin K1 are also among the best sources of many other heart-protecting nutrients. Included in this heart-protective list from green leafy vegetables would be the vitamins A (in the form of carotenoids), C, E and B6, the minerals potassium and magnesium, and dietary fiber.

Researchers have attempted to answer this question by giving vitamin K in pill form at amounts similar to those found in the diet. Over a three-year period, 500 mcg of vitamin K—about the amount found in one serving of mustard greens—was associated with slightly slower progression of hardening of the arteries of the heart.

Given the preliminary and somewhat contradictory nature of this research, we would characterize the association between diets high in vitamin K and protection against coronary artery disease to be plausible, but still unproven.

Bone Health

Vitamin K is a fascinating nutrient with respect to bone health, and unlike some of the open-ended questions related to clotting, knowledge about the role of vitamin K nourishment in bone support is fairly well-established. Individuals who are vitamin K deficient have repeatedly been shown to have a greater risk of fracture. In addition, for women who have passed through menopause and have started to experience unwanted bone loss, vitamin K has clearly been shown to help prevent future fractures.

Bone support involves different forms of vitamin K

Research has shown that our bone cells take up vitamin K in the form of K1 as well as K2, suggesting that these forms of the vitamin may play different roles in the health of our bone. In the case of K2, researchers have also become interested in two particular subtypes of K2 called MK-4 and MK-7, which appear to be uptaken by our bone cells in preference to other subtypes. In fact, research on bone health is partly responsible for getting researchers more and more interested in the whole issue of vitamin K2 subtypes. Vitamin K2 contains a chemical “tail” composed of repeating units called prenyl units. The most common forms of K2 contain either 4,5,7,8, or 9 prenyl units, and are therefore referred to as MK-4, MK-5, MK-7, MK-8, and MK-9. (The letter “M” in “MK” refers to “menaquinone”—the scientific name for the K2—and the “K” refers to the common name of vitamin K.) While human diets usually consist of about 10-25% K2, the proportion of these different K2 forms can vary widely. Fermented soy foods (mentioned earlier in this article as an important source of K2) tend to have greater amounts of MK-7. Cheese may have greater amounts of MK-8 and MK-9. However, in the average U.S. diet, MK-4 typically accounts for about one-third or more of all K2 due to its presence in eggs and meats.

How bone support works

The bone-related benefits of vitamin K appear to depend on at least two basic mechanisms. The first of these mechanisms involves a type of bone cell called osteoclasts. Osteoclasts are bone cells in charge of bone demineralization—they help take minerals out of the bone and make them available for other body functions. While the activity of these cells is important for proper health, we do not want too many osteoclasts (or too much activity by osteoclasts) since those imbalances would mean too much demineralization of bone. Vitamin K helps our body keep this process in check. The MK-4 form of vitamin K2 (also called menatetrenone) is known to block formation of too many osteoclasts, and perhaps also to initiate their programmed cell death (a process called apoptosis).

A second mechanism involves the role of vitamin K in a process called carboxylation. (This process is the same one discussed earlier in relationship to the stickiness of clotting factors required for proper blood clotting.) For our bones to be optimally healthy, one of the proteins found in bone—a protein called osteocalcin—needs to be chemically altered through the process of carboxylation. (Osteocalcin is not just any typical bone protein. It is a protein especially linked to our bone mineral density (BMD), and for this reason, it often measured in our blood when doctors are seeking to determine the health of our bone.) When too few of the osteocalcin proteins in our bone are carboxylated, our bones have increased risk for fracture. This unwanted risk appears to be particularly important with respect to hip fracture. Scientists refer to this bone problem as a problem involving “undercarboxylated osteocalcin” and they have determined that vitamin K can greatly improve the situation. Since vitamin K is required for proper activity of the carboxylase enzyme that allows carboxylation of the osteocalcin proteins in our bone, vitamin K can help restore these bone proteins to their proper place in our bone structure and strengthen the composition of the bone. In clinical studies, both K1 and K2 forms of vitamin K appear to play a role in osteocalcin carboxylation. Some studies show the K2 form (and specifically MK-4) to be especially helpful in postmenopausal bone protection.

Whether provided by the diet in the form of K1 or K2, this vitamin is becoming more and more focal in research on bone protection. Low levels of vitamin K intake are emerging as dietary risk factors for osteoporosis. Researchers have shown that increasing dietary vitamin K intake by 100 mcg per day—roughly doubling the average American adult intake for a time period of one full year—can lead to a significant increase in bone density in post-menopausal women. Low levels of vitamin K have also been associated with increased risk of arthritis. Low activity of vitamin K-dependent proteins inside the joints has been suggested as a likely mechanism for this increased risk.

Other Potential Health Benefits

Not suprisingly based on its role in photosynthesis and movement of electrons to generate energy, vitamin K may function as an important antioxidant nutrient especially in certain chemical forms (called “reduced” forms). In older men, vitamin K has been shown to help improve insulin resistance. In preliminary lab and animal studies, vitamin K has been investigated as a critical nutrient for protecting cells that line blood vessels, including both veins and arteries.

Summary of Food Sources

Both plant and animal foods can provide us with significant amounts of vitamin K. Fresh green vegetables are our most steadfast source of K1. At WHF, 16 of our green vegetables rank as excellent sources for this vitamin. Many of our Herbs & Spices—including parsley, basil, cilantro, sage, oregano and black pepper—also provide excellent amounts of vitamin K.

One serving of any food noted above will provide you with at least 10% of your daily vitamin K needs. In the case of kale—our top source of vitamin K—a 1-cup serving will provide you with over 1,000 micrograms, which is approximately 10 times the recommended minimum daily amount! Since the National Academy of Sciences has chosen not to set a maximal recommended intake level (Tolerable Upper Limit, or UL) based on available research, you will not be exceeding a recommended maximum amount even with ten times the minimum requirement (or greater amounts).

Outside of the vegetable family, you will find kiwifruit, blueberries, prunes, and grapes amount the most vitamin K-rich fruit sources, and soybeans and miso as two good legume sources. As mentioned earlier, most of our featured animal foods—including pasture-raised eggs, pasture-raised chicken, grass-fed beef, grass-fed lamb, grass-fed cheese, and grass-fed cow’s milk—contain measurable amounts of vitamin K, as do shrimp, sardines, tuna, and salmon.

As you can see, nearly half of our WHF (44/100) rank as good, very good, or excellent sources of vitamin K. Your meal combinations for achieving ample vitamin K here are extensive. Still, as a fallback source for vitamin K1, you would most likely want to turn to dark green leafy vegetables since they typically provide 500-1,000 micrograms per serving. For vitamin K2, you would mostly likely want to turn to fermented plant foods (like miso or tempeh) or animal foods. As mentioned earlier, fermented plant foods and animal foods feature different subtypes of vitamin K2. Remember, however, that researchers know of no hard and fast requirement for consuming any set amount of preformed K2 from your meal plan since the cells of your body are able to take K1 and convert it into K2. This provides you with a lot of flexibility in choosing among the 40+ WHF that are ranked sources of this vitamin.

Common name

Vitamin K1

Vitamin K2

Vitamin K3

Scientific name

phylloquinones

menaquinones

menadiones

Food sources

plant foods, especially dark green leafy vegetables

meats, eggs, dairy, fish, fermented plant foods, fermented animal foods

not known to be provided in substantial, naturally occurring amounts in food

Nutrient Rating Chart

Introduction to Nutrient Rating System Chart

Read more background information and details of our rating system

WHF ranked as quality sources of
vitamin K

Food

Serving
Size

Cals

Amount
(mcg)

DRI/DV
(%)

Nutrient
Density

World’s
Healthiest
Foods Rating

Kale

1 cup

36.4

1062.10

1180

583.6

excellent

Spinach

1 cup

41.4

888.48

987

429.2

excellent

Mustard Greens

1 cup

36.4

829.78

922

455.9

excellent

Collard Greens

1 cup

62.7

772.54

858

246.4

excellent

Beet Greens

1 cup

38.9

696.96

774

358.5

excellent

Swiss Chard

1 cup

35.0

572.77

636

327.3

excellent

Turnip Greens

1 cup

28.8

529.34

588

367.6

excellent

Parsley

0.50 cup

10.9

498.56

554

911.4

excellent

Broccoli

1 cup

54.6

220.12

245

80.6

excellent

Brussels Sprouts

1 cup

56.2

218.87

243

77.9

excellent

Romaine Lettuce

2 cups

16.0

96.35

107

120.6

excellent

Asparagus

1 cup

39.6

91.08

101

46.0

excellent

Basil

0.50 cup

4.9

87.94

98

360.4

excellent

Cabbage

1 cup

43.5

71.40

79

32.8

excellent

Bok Choy

1 cup

20.4

57.80

64

56.7

excellent

Celery

1 cup

16.2

29.59

33

36.6

excellent

Kiwifruit

1 2 inches

42.1

27.81

31

13.2

excellent

Leeks

1 cup

32.2

26.42

29

16.4

excellent

Cilantro

0.50 cup

1.8

24.80

28

269.6

excellent

Sage

2 tsp

4.4

24.00

27

108.8

excellent

Green Beans

1 cup

43.8

20.00

22

9.1

excellent

Cauliflower

1 cup

28.5

17.11

19

12.0

excellent

Cucumber

1 cup

15.6

17.06

19

21.9

excellent

Tomatoes

1 cup

32.4

14.22

16

8.8

excellent

Oregano

2 tsp

5.3

12.43

14

46.9

excellent

Black Pepper

2 tsp

14.6

9.49

11

13.0

excellent

Green Peas

1 cup

115.7

35.68

40

6.2

very good

Blueberries

1 cup

84.4

28.56

32

6.8

very good

Grapes

1 cup

104.2

22.05

25

4.2

very good

Carrots

1 cup

50.0

16.10

18

6.4

very good

Summer Squash

1 cup

36.0

6.30

7

3.5

very good

Cloves

2 tsp

11.5

5.96

7

10.4

very good

Chili Peppers

2 tsp

15.2

5.71

6

7.5

very good

Soybeans

1 cup

297.6

33.02

37

2.2

good

Avocado

1 cup

240.0

31.50

35

2.6

good

Raspberries

1 cup

64.0

9.59

11

3.0

good

Winter Squash

1 cup

75.8

9.02

10

2.4

good

Pear

1 medium

101.5

7.83

9

1.5

good

Cranberries

1 cup

46.0

5.10

6

2.2

good

Miso

1 TBS

34.2

5.04

6

2.9

good

Bell Peppers

1 cup

28.5

4.51

5

3.2

good

Plum

1 2-1/8 inches

30.4

4.22

5

2.8

good

Cantaloupe

1 cup

54.4

4.00

4

1.5

good

Eggplant

1 cup

34.6

2.87

3

1.7

good

World’s Healthiest
Foods Rating

Rule

excellent

DRI/DV>=75% OR
Density>=7.6 AND DRI/DV>=10%

very good

DRI/DV>=50% OR
Density>=3.4 AND DRI/DV>=5%

good

DRI/DV>=25% OR
Density>=1.5 AND DRI/DV>=2.5%

Impact of Cooking, Storage and Processing

Vitamin K is a fairly stable nutrient to most types of processing. Levels go down only slightly with common cooking techniques and tend to stay stable with storage.

Vitamin K in oils, but probably not in vegetables, is reduced by exposure to light. This is one reason, but certainly not the only one, that we recommend storing oils in dark areas and in opaque, sealed containers.

The hydrogenation process that is used to stabilize and solidify liquid fats damages a significant amount of the vitamin K content. This is just one of many reasons why we believe that hydrogenated fats should be avoided.

Risk of Dietary Deficiency

Average intake of vitamin K for U.S. adults has been estimated at approximately 80-85 micrograms per day, or about 70-90% of recommended intake. At WHF, we adopted the DRI standard for women 19 years and older of 90 micrograms per day as the one we use in our Nutrient Rating Charts, and on average, U.S. adults fall below this amount. In terms of age groups, adolescents and young adults have more risk of dietary deficiency than older adults, and men have more risk of deficiency than women, perhaps in part because the DRI for men age 19 years and older is 120 micrograms, or one-third higher than the DRI for women.

In light of the many foods that are rich in vitamin K—especially green vegetables—these averages tell us that on average, we are consuming very few green vegetables. For example, a single one-cup serving or broccoli each day would more than double our average vitamin K intake.

As described above, it would not take many food changes to help us move from our average marginal intake of vitamin K to a more optimal level. Increasing our intake of the WHF would be a great way to make this shift, especially if green vegetables were given center stage.

Other Circumstances that Might Contribute to Deficiency

Apart from low dietary intake, the most common reason to see symptoms of vitamin K deficiency at least related to blood clotting involves use of medications that deliberately block the ability of vitamin K to help make blood clotting proteins. For people using these medications, there are specific medical reasons for trying to reduce vitamin K’s ability in this regard. Anyone taking anti-coagulant medications should talk to their doctor about dietary intake of vitamin K and how to coordinate it with their overall health goals.

There are a few disease states that can interfere with vitamin K nutrition or utilization. For instance, any digestive disease that impairs absorption of fat-soluble nutrients may impair vitamin K uptake from foods. End-stage liver disease can also lead to symptoms of vitamin K deficiency. However, these problems are once again medical in nature, rather than lifestyle oriented and widely encountered by the general public.

Relationship with Other Nutrients

Both vitamin A and vitamin E can compete for absorption with vitamin K. To our knowledge, however, this has only been reported with mega-dose supplementation, not with dietary intake. As such, you probably do not need to eat in a certain pattern to protect your vitamin K nutrition, and you can enjoy the delicious taste of foods that are rich in all of these important nutrients.

Vitamin K works with the other nutrients important to bone health—calcium, vitamin D, and magnesium—to ensure that your skeleton stays strong. A deficiency of any of these nutrients can lead to problems that cannot be fully undone by focusing on other nutrients in the list.

Risk of Dietary Toxicity

To our knowledge, there has never been a report of a person consuming a toxic dose of vitamin K from food, unless that person was taking a prescription medication specifically designed to affect vitamin K activity. Given the strong track record of safety, the National Academy of Sciences has chosen not to establish a Tolerable Upper Intake Level (UL) for vitamin K. Further evidence for the safety of dietary vitamin K comes from research studies where doses of vitamin K at 500 times the Dietary Reference Intake (DRI) level did not lead to observable toxicity.

The absence of a recommended maximum intake level is good news for anyone who enjoys vegetable-rich meals and especially those meals containing or more of our 44 top-ranked vitamin K-containing vegetables. Two or three of these vegetables can easily provide 10 times the WHF recommended intake amount of 90 micrograms. However, just to reiterate a point we made earlier in this section: risk of excessive vitamin K intake still applies to individuals who are taking prescription medications designed to regulate the activity of vitamin K, and any individual in this category should discuss dietary vitamin K intake with their healthcare provider.

Disease Checklist

• Blood clotting disorders
• Osteoporosis
• Coronary artery disease
• Cancer
• Liver disease
• Celiac disease
• Crohn’s disease
• Ulcerative colitis
• Cystic fibrosis

Public Health Recommendations

• 0-6 months: 2 mcg
• 6-12 months: 2.5 mcg
• 1-3 years: 30 mcg
• 4-8 years: 55 mcg
• 9-13 years: 60 mcg
• 14-18 years: 75 mcg
• 19+ years, female: 90 mcg
• 19+ years, male: 120 mcg
• Pregnant or lactating women, 14-18 years: 75 mcg
• Pregnant or lactating women, 19+ years: 90 mcg

The 2001 vitamin K DRIs did not include any Tolerable Upper IntakeLevels (ULs). We are not aware of any other public health organization that has issued a maximum level for dietary intake of vitamin K.

The Daily Value (DV) for vitamin K is 80 micrograms. This is the value that you’ll see on food and supplement labels.

At WHF, we selected the DRI of 90 micrograms for women ages 19 and above as our recommended daily intake level.

What events can indicate a need for more high-vitamin K foods?

• Excessive bleeding, including heavy menstrual bleeding, gum bleeding, bleeding within the digestive tract, or nosebleeding
• Easy bruising
• Problems with calcification of the blood vessels or heart valves
• Problems with bone fracture or bone weakening

Excellent sources of vitamin K include parsley, kale, spinach, Brussels sprouts, Swiss chard, green beans, asparagus, broccoli, kale, mustard greens, turnip greens, collard greens, thyme, romaine lettuce, sage, oregano, cabbage, celery, sea vegetables, cucumber, leeks, cauliflower, tomatoes, and blueberries.

WHF rich in
vitamin K

FoodCals%Daily Value

Kale361327.6%

Spinach411110.6%

Collard Greens491045%

Swiss Chard35715.9%

Turnip Greens29661.6%

Mustard Greens21524.1%

Brussels Sprouts38194.7%

Parsley3155.8%

Romaine Lettuce16120.4%

Broccoli31115.5%

For serving size for specific foods, see Nutrient Rating Chart below at the bottom of this page.

• Description

• Function

• Deficiency Symptoms

• Toxicity Symptoms

• Cooking, storage and processing

• Factors that affect function

• Nutrient interaction

• Health conditions

• Food Sources

• Public Health Recommendations

• References

Description

What is vitamin K?

Vitamin K is not a single chemical substance but rather a family of chemically related substances that go by the general name of “vitamin K.” Over the past 20 years, no vitamin family has undergone a greater change in terms of our scientific understanding of its chemistry and function. In the past, members of the vitamin K family have traditionally been referred to as vitamin K1, vitamin K2, and vitamin K3. This terminology is largely being replaced by a different set of terms to describe what has now been determined to be a more complicated set of vitamin K compounds.

All types of vitamin K fall into a large chemical category of substances called naphthoquinones. Within this naphthoquinone category, there are two basic types of vitamin K. The first type, called phylloquinones, is made by plants. The second basic type, called menaquinones, is made by bacteria. (The only exception to this rule involves a special group of bacteria, called cyanobacteria, which make phylloquinones instead of menaquinones.) Contrary to some previous scientific assumptions, we get most of our dietary vitamin K in the form of phylloquinones from plant foods. In fact, up to 90% of our dietary vitamin K comes in this form, and within that 90%, over half comes from vegetables— especially green leafy vegetables. Many different types of bacteria in our intestines can make vitamin K in the form of menaquinones. While this synthesis of vitamin K in our digestive tract can contribute to our vitamin K requirements, this contribution is less than previously thought.

How it Functions

What are the functions of vitamin K?

Promotes healthy blood clotting

In terms of health research, vitamin K is best known for its role in healthy blood clotting. In fact, use of the letter “K” in the very name of this vitamin originally came from the German word koagulation.

Although blood clotting may not sound like a body process that is critical for our everyday health, it is, in fact, essential. At one end of the spectrum, whenever we get a skin wound (even a simple cut) we need sufficient blood clotting ability to close the wound and prevent excessive bleeding. At the other end of the spectrum, we do not want too much blood clotting ability because when we are not wounded, we do not want our cardiovascular system to “throw a clot” and mistakenly block an otherwise functioning blood vessel. Vitamin K is one of the key nutrients for keeping our blood clotting ability at the exact right level.

We owe much of our understanding about vitamin K and clotting to early experiments with the prescription drug warfarin. Also known under the brand name Coumadin, warfarin is a widely used anticoagulant drug that works by inhibiting the body’s synthesis of clotting factors (including clotting factors II, VII, IX, and X).

Vitamin K sits right at the center of this clotting process. If clotting factors are to successfully close a wound, they need some way to stick onto the nearby tissue surfaces. What provides them with this “stickiness” is a chemical event called carboxylation. One of the amino acids in the clotting factors, called glumatic acid, is the component of the clotting factors that gets carboxylated. Two enzymes are needed to keep this process running smoothly. Warfarin works as an anticoagulant and interrupts this process by blocking one of those enzymes (vitamin K epoxide reductase). When this enzyme is blocked, vitamin K can no longer be recycled and recharged to help the clotting factors achieve their proper stickiness. For individuals with an excessive tendency to form blood clots, anticoagulant drugs like warfarin can be life saving. These warfarin-related discoveries have led to our current understanding of vitamin K as a key nutrient for healthy blood clotting.

Protects bones from weakening or fracture

The relationship of vitamin K to bone health has been fairly well researched, and in the big picture, vitamin K has emerged as a critical nutrient for bone health. Most convincing is research showing protection from bone fractures that occurs when vitamin K is consumed in adequate amounts. Individuals who are vitamin K deficient have been clearly shown to have a greater risk of fracture. In addition, for women who have passed through menopause and have started to experience unwanted bone loss, vitamin K has been clearly shown to help prevent future fractures. These bone-related benefits of vitamin K appear to depend on at least two basic mechanisms.

The first of these mechanisms involves a type of bone cells called osteoclasts. Osteoclasts are bone cells in charge of bone demineralization. They help take minerals out of the bone and make them available for other body functions. While the activity of these cells is important for proper health, we do not want too many osteoclasts (or too much activity by osteoclasts) since those imbalances would mean too much bone demineralization. Vitamin K makes it possible for our body to keep this process in check. One of the menaquinone forms of vitamin K (MK-4, also called menatetrenone) has repeatedly been show to block formation of too many osteoclasts and perhaps also to initiate their programmed cell death (a process called apoptosis).

A second mechanism involves the role of vitamin K in a process called carboxylation. (This process is the same one discussed earlier in relationship to the stickiness of clotting factors required for proper blood clotting.) For our bones to be optimally healthy, one of the proteins found in bone—a protein called osteocalcin—needs to be chemically altered through the process of carboxylation. (Osteocalcin is not just any typical bone protein. It is a protein especially linked to our bone mineral density (BMD) and for this reason, it is often measured in our blood when doctors are seeking to determine the health of our bone.) When too few of the osteocalcin proteins in our bone are carboxylated, our bones have increased risk for fracture. This unwanted risk appears to be particularly important with respect to hip fracture. Scientists refer to this bone problem as one involving “undercarboxylated osteocalcin,” and they have determined that vitamin K can greatly improve the situation. Since vitamin K is required for proper activity of the carboxylase enzyme that allows carboxylation of the osteocalcin proteins in our bone, vitamin K can restore these bone proteins to their proper place in our bone structure and strengthen the composition of the bone. It is the MK-4 menaquinone form of vitamin K that has been best researched in this regard.

Prevents calcification of blood vessels or heart valves

One common problem in many forms of cardiovascular disease is unwanted calcification, the build-up of calcium inside a tissue that is normally soft. This build-up of calcium causes the tissue to harden and stop functioning properly. When calcium builds up inside the arteries, it is typically referred to as hardening of the arteries. One direct way to inhibit the build-up of calcium along the arteries is to maintain ample supplies of a special protein called MGP in the body. MGP, or matrix Gla protein, directly blocks the formation of calcium crystals inside the blood vessels. For MGP to function in this way, it must first be present in its carboxylated form; vitamin K is required for this carboxylation process. In other words, the heart-protective benefits of MGP in prevention of calcification depend upon vitamin K. In animal studies, both basic forms of vitamin K—i.e., phylloquinones and menaquinones—have been found to provide excellent calcification-preventing benefits. Researchers have determined that individuals with vitamin K deficiency are at greater risk for hardening of the arteries than individuals with healthy vitamin K intake.

Other roles for vitamin K

Researchers continue to explore a wide range of health-supportive roles for vitamin K. At the forefront of this research are roles in three basic areas: (1) protection against oxidative damage; (2) proper regulation of inflammatory response; and (3) support of brain and nervous system structure. With respect to protection against oxidative damage, vitamin K does not appear to function directly as an antioxidant in the same manner that other antioxidant vitamins (like vitamin E and vitamin C) do. Yet, both phylloquinone and menaquinone forms of vitamin K appear helpful in protecting cells—particularly nerve cells - from oxidative damage. In terms of inflammatory response, several markers of pro-inflammatory activity—including, for example, release of interleukin-6 (IL-6)—are significantly lowered by healthy vitamin K levels. Finally, with regard to brain and nervous system structure, vitamin K is known to be required for synthesis of a very important family of brain and nervous system fats called sphingolipids. These fats are critical in the formation of the myelin sheath that forms an outer wrapping around the nerves, and both phylloquinone and menaquinone forms of vitamin K have been found effective in supporting synthesis of these key nervous system components. All of the above roles for vitamin K have been investigated primarily in laboratory studies on animals or in laboratory studies on human cell samples.

Deficiency Symptoms

What are deficiency symptoms for vitamin K?

Persons deficient in vitamin K are first and foremost likely to have symptoms related to problematic blood clotting or bleeding. These symptoms can include heavy menstrual bleeding, gum bleeding, bleeding within the digestive tract, nose bleeding, easy bruising, blood in the urine, prolonged clotting times, hemorrhaging, and anemia. A second set of vitamin K deficiency-related symptoms involves bone problems. These symptoms can include loss of bone (osteopenia), decrease in bone mineral density (osteoporosis), and fractures—including common age-related fractures like that of the hips. Yet another set of vitamin K deficiency-related symptoms involves excess deposition of calcium in soft tissues. These calcification-based problems include hardening of the arteries or calcium-related problems with heart valve function.

Toxicity Symptoms

What are toxicity symptoms for vitamin K?

Since no adverse effects have been reported for higher levels of vitamin K intake from food and/or supplements, there are no documented toxicity symptoms for vitamin K. Levels as high as 340 micrograms per day have been reported in U.S. diets, and if dietary supplements are included, daily intake levels as high as 367 micrograms have been reported. In animal studies, vitamin K has been provided in amounts as high as 25 micrograms per kilogram of body weight (or for an adult human weighing 154 lbs, the equivalent of 1,750 micrograms of vitamin K) without noticeable toxicity. For these reasons, the Institute of Medicine at the National Academy of Sciences chose not to set a Tolerable Upper Limit (UL) for vitamin K when it revised its public health recommendations for this nutrient in 2000.

One important exception to these toxicity results involves a synthetic form of vitamin K called menadione. While this form of vitamin K can sometimes be converted by the body into non-toxic forms, research studies have shown unwanted risk stemming from intake of menadione. This risk involves excessive oxidative stress and resultant damage to a variety of cell types, including kidney and liver cells. Based on these findings, the U.S. Food and Drug Administration (FDA) does not allow vitamin K to be sold as a dietary supplement in its menadione form. (Menadione is also commonly referred to as Vitamin K3.)

Factors that Affect Function

What factors might contribute to a deficiency of vitamin K?

Any health problems that compromise digestion and/or absorption of nutrients can contribute to deficiency of vitamin K. These problems include health conditions like inflammatory bowel disease, ulcerative colitis, celiac disease, short bowel syndrome, and digestive tract surgeries (like intestinal resection). Problems with pancreatic function, liver function, or gallbladder function can also increase our risk of vitamin K deficiency.

Because our intestinal bacteria help supply us with vitamin K, any drugs that alter our normal intestinal bacteria can compromise our vitamin K status. At the top of this drug list would be antibiotics but also included would be some anti-seizure medications, sulfa-drugs, and salicylate-containing drugs. (If you regularly use a medication in any of the above groups, we recommend a discussion with your doctor about potential impact on vitamin K.)

There is some evidence that the process of aging itself may contribute to deficiency of vitamin K. The reasons for this potential connection between aging and vitamin K are not clear. Changes in overall metabolism, for example, may be involved alongside of other more specific changes directly related to vitamin K. But whatever the underlying reason, it may be especially important for us to take a close look at our vitamin K intake as we age.

Nutrient Interactions

How do other nutrients interact with vitamin K?

Research on nutrient-nutrient interactions with vitamin K has traditionally focused on the major fat-soluble vitamins—namely, vitamins A, E, and D. Unfortunately, this research has shown some mixed results and in some areas of research, the jury is still out. Persons undergoing treatment with anticoagulant drugs have clearly been shown to have their anticoagulant therapy and their vitamin K status impacted by high doses of vitamin E. For this reason, intake of both vitamin K and vitamin E for persons undergoing treatment with anticoagulant medications needs to be determined with the help of a healthcare provider. In healthy persons, no food intake of vitamin E has been shown to compromise vitamin K status. However, under some circumstances, higher supplement intake of vitamin E (above 1,000 milligrams) has been shown to interfere with vitamin K function and, in some cases, to promote hemorrhaging. Largely based on these hemorrhagic effects, the National Academy of Sciences set a Tolerable Upper Limit (UL) of 1,000 milligrams per day for vitamin E in 2000.

Since calcium metabolism can be greatly affected by both vitamin D and vitamin K, researchers suspect some key interactions between these two fat-soluble vitamins. However, the exact nature of this interaction has yet to be determined.

Similar to the research on vitamin E in food, no food intake of vitamin A has been show to compromise vitamin K status. However, excess supplemental intake of vitamin A (in its retinol form) has been shown to interfere with the vitamin K-related clotting ability of the blood (and to cause a condition called hypothrombinemia). The amount of vitamin A triggering this potential problem with vitamin K status in adults is typically 10,000 IU (3,000 micrograms) or higher.

Health Conditions

What health conditions require special emphasis on vitamin K?

Vitamin K may play a role in the prevention and/or treatment of the following health conditions:

• Anticoagulant therapy
• Bone fracture
• Chronic liver disease
• Cystic fibrosis
• Hardening of the arteries
• Inflammatory bowel disease
• Liver cancer
• Pancreatic cancer
• Kidney stones
• Nausea and vomiting during pregnancy
• Osteopenia (bone loss)
• Osteoporosis (decreased bone mineral density)
• Thrombosis

Food Sources

Drug-Nutrient Interactions

What medications affect vitamin K?

Anticoagulant medications fall into a special category with respect to vitamin K status. Many anticoagulant medications (like warfarin, an anticoagulant widely sold under the brand name Coumadin) are designed to decrease the risk of unwanted blood clotting by interfering with vitamin K metabolism. For this reason, it is essential for individuals taking anticoagulants to discuss vitamin K intake with their doctors. The goal in this situation is to balance out two key health support factors: (1) continuation of ample vitamin K intake and (2) avoidance of excessive vitamin K intake that might compromise the anticoagulant benefits of the medication.

Some cholesterol-lowering drugs that work by tying up bile acids (called bile acid sequestrants) can also reduce absorption of vitamin K. Included here is the drug cholestyramine (often sold under the brand name Questran).

Antibiotics can decrease the availability of vitamin K by killing gut bacteria that synthesize vitamin K. Broad-spectrum antibiotics may pose the greatest risk in this regard. Included in this antibiotic category would be the sulfonamide antibiotics.

Other types of drugs that may decrease availability of vitamin K include high doses of salicylates (possibly including acetylsalicylic acid, or aspirin) and high doses of aluminum hydroxide antacids.

Form in Dietary Supplements

What forms of vitamin K are found in dietary supplements?

Both phylloquinone and menaquinone forms of vitamin K are widely available in dietary supplement form. In the case of the menaquinones, supplements are also available with specific amounts of select menaquinones. For example, it is possible to buy a supplement with purified amounts of a single menaquinone like MK-4 or MK-7. In the case of MK-7, this specific menaquinone form of vitamin K is often extracted from a fermented soybean culture in which the bacterium Bacillus subtilus natto was used to help produce the MK-7 from the soybeans. Some supplements advertise �full spectrum vitamin K.� This phrase usually refers to a combination of both phylloquinones and menaquinones. Supplements also commonly refer to the phylloquinone family of compounds as vitamin K1 and the menaquinone family of compounds as K2. However, as described earlier, this earlier terminology for vitamin K does not automatically indicate which specific phylloquinones or menaquinones are present in the supplement. For example, a supplement described as �vitamin K2� might or might not contain MK-7. Menadione (also referred to as vitamin K3) is one form of vitamin K not allowed in dietary supplements.

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