vitamin K

What can high-vitamin K foods do for you?

• Allow your blood to clot normally
• Help protect your bones from fracture
• Help prevent postmenopausal bone loss
• Help prevent calcification of your arteries
• Provide possible protection against liver and prostate cancer

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: spinach, Brussels sprouts, Swiss chard, green beans, asparagus, broccoli, kale and mustard greens. Very good sources include green peas and carrots.

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

Drug-nutrient interaction Nutrient interaction Health conditions Supplements Food Sources Public 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.)

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect vitamin K?

As a general rule, vitamin K is a resilient nutrient and is fairly well retained in most cooked or stored foods. We realize that some websites caution heavily against the freezing of some vegetables due to potential loss of vitamin K, but we have not seen research that documents this risk. In fact, the vast majority of research studies show a range of vitamin K values for raw/fresh, frozen, and cooked foods that varies by about 20-30% for any particular food. It is difficult to draw any hard and fast conclusions from this range of values because there can be at least a 20-30% variation in vitamin K between different varieties of the same food, especially when grown under different circumstances (for example, in different countries).

With respect to cooking, studies at the Nutrient Data Laboratory (part of the Agricultural Research Service at the U.S. Department of Agriculture's facility in Beltsville, MD) have shown heating to cause no major loss of vitamin K in vegetables. In some cases, cooking actually appears to increase the measurable amount of vitamin K. Researchers have speculated that this increase in vitamin K following heating may be due to the location of the vitamin K in the vegetables. Because the phylloquinone forms of vitamin K are located in the chloroplast components of the plant cells, cooking might be able to disrupt the plant cell walls and release some of the vitamin K, which then would get measured in the laboratory where it would otherwise go undetected. Whether this release of vitamin K from the chloroplasts improves the availability of vitamin K in our body has not been determined. But in any event, the cooking of vegetables does not appear to affect their vitamin K content in a negative way.

Commercial processing, however, is another matter. Particularly with respect to fruits and their commercial processing into fruit juice, we've seen evidence of dramatic vitamin K loss. While we have not seen evidence about the juicing of fresh fruits at home, we suspect that home juicing would have far less impact on the vitamin K found in fruits (or vegetables, if fresh vegetables were being juiced).

In summary, research shows that the freezing and storing of vegetables and fruits and the heating of these foods are practices that do not cause excessive loss of vitamin K. Therefore, excellent vitamin K nourishment does not depend on consumption of raw/fresh foods (even though raw/fresh foods may be outstanding components of a diet for many other reasons).

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.

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.

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

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.

Food Sources

What foods provide vitamin K1?

Excellent sources of vitamin K include: spinach, Brussels sprouts, Swiss chard, green beans, asparagus, broccoli, kale and mustard greens. Very good sources include green peas and carrots.

Fermentation of foods can be especially helpful for increasing their vitamin K content. Within this fermentation category, soy foods have a special place in the nutrition research on vitamin K since fermented soy foods play a unique role in supplying vitamin K in certain traditional cuisines (like that of Japan). You will sometimes find the word "natto" being used to refer to these fermented soy foods since Bacillus natto are bacteria that can convert K1 into K2 and are often used in the production of fermented soy products. Yet, fermented soy foods are not alone in the vitamin K-rich fermented foods category. Some cheeses are also fermented in a way that optimizes their vitamin K content. Proprioni bacteria, for example, make large amounts of one type of menaquinone called MK-9(H4) and cheeses fermented by these bacteria can be a rich source of vitamin K. Swiss Emmental cheese and Norwegian Jarlsberg cheeses are examples of cheeses fermented by proprioni bacteria.

In the average U.S. diet, meats and eggs are the most common food sources of the menaquinone MK-4. Fermented soy foods are our most common source of MK-7. (Remember that all forms of vitamin K including menaquinones like MK-4 and MK-7 and also phylloquinones make great contributions to our health.)

Many forms of lettuce contain worthwhile amounts of vitamin K. It is worth noting here that on an ounce-per-ounce basis, romaine lettuce may be about four times higher in vitamin K than iceberg lettuce according to studies conducted at the U.S. Department of Agriculture.

Since vitamin K is a fat-soluble family of nutrients, foods tend to become higher in vitamin K as they become less concentrated with water. For example, on an ounce-for-ounce basis, tomato paste is higher in vitamin K than fresh tomatoes.

Sometimes the outer leaves of a plant can be more concentrated in vitamin K than the inner leaves. We've seen research documenting this difference for both cabbage and Brussels sprouts. For this reason, it may be worthwhile to very carefully and gently scrub these vegetables with a natural bristle brush while rinsing them under a flow of clean water as a way to clean the other leaves and keep them included in your meal rather than simply discarding these outside leaves due to presence of dirt or other particles.

 

Introduction to Nutrient Rating System Chart

In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the World's Healthiest Foods that are either an excellent, very good, or good source of vitamin K. Next to each food name, you'll find the serving size we used to calculate the food's nutrient composition, the calories contained in the serving, the amount of vitamin K contained in one serving size of the food, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling." Read more background information and details of our rating system.

World's Healthiest Foods ranked as quality sources of: vitamin K
Food	Serving Size	Cals	Amount (mcg)	DV (%)	Nutrient Density	World's Healthiest Foods Rating
Parsley, fresh	2 tbs	2.7	123.00	153.8	1025.0	excellent
Kale, boiled	1 cup	36.4	1062.10	1327.6	656.5	excellent
Spinach, boiled	1 cup	41.4	888.48	1110.6	482.9	excellent
Mustard greens, boiled	1 cup	21.0	419.30	524.1	449.2	excellent
Turnip greens, cooked	1 cup	28.8	529.34	661.7	413.5	excellent
Swiss chard, boiled	1 cup	35.0	572.80	716.0	368.2	excellent
Collard greens, boiled	1 cup	49.4	704.00	880.0	320.6	excellent
Romaine lettuce	2 cup	15.7	114.80	143.5	164.7	excellent
Basil, dried, ground	2 tsp	7.5	48.01	60.0	143.6	excellent
Thyme, dried, ground	2 tsp	7.9	48.01	60.0	136.4	excellent
Brussel sprouts, boiled	1 cup	60.8	218.80	273.5	80.9	excellent
Broccoli, steamed	1 cup	43.7	155.20	194.0	79.9	excellent
Cabbage, shredded, boiled	1 cup	33.0	73.35	91.7	50.0	excellent
Asparagus, boiled	1 cup	43.2	91.80	114.8	47.8	excellent
Oregano, dried, ground	2 tsp	9.2	18.65	23.3	45.8	excellent
Celery, raw	1 cup	19.2	35.26	44.1	41.3	excellent
Kelp (sea vegetable)	0.25 cup	8.6	13.20	16.5	34.5	excellent
Black pepper	2 tsp	10.9	6.88	8.6	14.2	very good
Green beans, boiled	1 cup	43.8	20.00	25.0	10.3	excellent
Cloves, dried, ground	2 tsp	14.2	5.96	7.5	9.4	very good
Cauliflower, boiled	1 cup	28.5	11.17	14.0	8.8	excellent
Tomato, ripe	1 cup	37.8	14.22	17.8	8.5	excellent
Green peas, boiled	1 cup	134.4	41.40	51.8	6.9	very good
Carrots, raw	1 cup	52.5	16.10	20.1	6.9	very good
Cayenne pepper, dried	2 tsp	11.2	2.89	3.6	5.8	good
Bell peppers, red, raw, slices	1 cup	24.8	4.51	5.6	4.1	very good
Summer squash, cooked, slices	1 cup	36.0	6.30	7.9	3.9	very good
Avocado, slices	1 cup	235.1	29.20	36.5	2.8	good
Miso	1 oz	70.8	8.53	10.7	2.7	good
Soybeans, cooked	1 cup	297.6	33.02	41.3	2.5	good
Cranberries	0.50 cup	23.3	2.42	3.0	2.3	good
Pumpkin seeds, raw	0.25 cup	186.7	17.73	22.2	2.1	good
Cow's milk, 2%	1 cup	121.2	9.76	12.2	1.8	good
Pear	1 each	97.9	7.47	9.3	1.7	good
Strawberries	1 cup	43.2	3.17	4.0	1.7	good
Papaya	1 each	118.6	7.90	9.9	1.5	good
Kidney beans, cooked	1 cup	224.8	14.87	18.6	1.5	good

World's Healthiest Foods Rating	Rule
excellent	DV>=75%	OR	Density>=7.6	AND	DV>=10%
very good	DV>=50%	OR	Density>=3.4	AND	DV>=5%
good	DV>=25%	OR	Density>=1.5	AND	DV>=2.5%

Public Health Recommendations

What are current public health recommendations for vitamin K?

In 2000, the National Academy of Sciences established the following Adequate Intake (AI) levels for vitamin K:

• Males and females, 0-6 months: 2 micrograms
• Males and females, 7-12 months: 2.5 micrograms
• Males and females, 1-3 years: 30 micrograms
• Males and females, 4-8 years: 55 micrograms
• Males and females, 9-13 years: 60 micrograms
• Males and females, 14-18 years: 75 micrograms
• Males, 19 years and older: 120 micrograms
• Females, 19 years and older: 90 micrograms
• Pregnant or lactating females, 18 years and younger: 75 micrograms
• Pregnant or lactating females, 19 years and older: 90 micrograms

References

• Adams J, Pepping J. Vitamin K in the treatment and prevention of osteoporosis and arterial calcification. Am J Health Syst Pharm 2005 Aug 1;62(15):1574-81. 2005.
• Basu TK, Donaldson D. Intestinal absorption in health and disease: micronutrients. Best Pract Res Clin Gastroenterol. 2003 Dec;17(6):957-79. 2003.
• Berkner KL. Vitamin K-dependent carboxylation. Vitam Horm 2008;78:131-56. 2008.
• Booth SL. Vitamin K status in the elderly. Vitam Horm 2008;78:1-22. 2008.
• Bugel S. Vitamin K and bone health in adult humans. Vitam Horm 2008;78:393-416. 2008.
• Cheung AM, Tile L, Lee Y, et al. Vitamin K supplementation in postmenopausal women with osteopenia (ECKO trial): a randomized controlled trial. PLoS Med. 2008 Oct 14;5(10):e196. 2008.
• Cockaybe S, Adamson J, Lanham-New S et al. Vitamin K and the Prevention of Fractures: Systematic Review and Meta-analysis. Arch Intern Med. 2006;166:1256-1261. 2006.
• Conly J, Stein K. Reduction of vitamin K2 concentrations in human liver associated with the use of broad spectrum antimicrobials. Clin Invest Med. 1994 Dec;17(6):531-9. 1994.
• Conway SP. Vitamin K in cystic fibrosis. J R Soc Med 2004;97 Suppl 44:48-51. 2004.
• Cranenburg EC, Schurgers LJ, Vermeer C. Vitamin K: the coagulation vitamin that became omnipotent. Thromb Haemost 2007 Jul;98(1):120-5. 2007.
• Danziger J. Vitamin K-dependent Proteins, Warfarin, and Vascular Calcification. J. Am. Soc. Nephrol. 2008;3:1504-1510. 2008.
• Erkkila AT, Booth SL. Vitamin K intake and atherosclerosis. Curr Opin Lipidol 2008 Feb;19(1):39-42 2008.
• Fisher L, Byrnes E, and Fisher AA. Prevalence of vitamin K and vitamin D deficiency in patients with hepatobiliary and pancreatic disorders. Nutr Res. 2009 Sep;29(9):676-83. 2009.
• Gutzeit D, Baleanu G, Winterhalter P, et al. Determination of processing effects and of storage stability on vitamin K1 (Phylloquinone) in Sea Buckthorn Berries (Hippophaë rhamnoides L. ssp. rhamnoides) and related products. J Food Sci. 2007 Nov;72(9):C491-7. 2007.
• Hey E. Vitamin K--what, why, and when. Arch Dis Child Fetal Neonatal Ed 2003 Mar;88(2):F80-3. 2003.
• Homma K, Wakana N, Suzuki Y, et al. Treatment of natto, a fermented soybean preparation, to prevent excessive plasma vitamin K concentrations in patients taking warfarin. J Nutr Sci Vitaminol (Tokyo) 2006 Oct;52(5):297-301. 2006.
• Huyghebaert N, De Beer J, Vervaet C, et al. Compounding of vitamin A, D3, E and K3 supplements for cystic fibrosis patients: formulation and stability study. 2007 Oct;32(5):489-96. 2007.
• Kamao M, Suhara Y, Tsugawa N, et al. Vitamin K content of foods and dietary vitamin K intake in Japanese young women. J Nutr Sci Vitaminol (Tokyo) 2007 Dec;53(6):464-70. 2007.
• Kuwabara A, Tanaka K, Tsugawa N et al. High prevalence of vitamin K and D deficiency and decreased BMD in inflammatory bowel disease. Osteoporos Int. 2009 Jun;20(6):935-42. 2009.
• Lamson DW, Plaza SM. The anticancer effects of vitamin K. Altern Med Rev 2003 Aug;8(3):303-18. 2003.
• Mager DR, McGee PL, Furuya KN et al. Prevalence of vitamin K deficiency in children with mild to moderate chronic liver disease. J Pediatr Gastroenterol Nutr. 2006 Jan;42(1):71-6. 2006.
• McCann JC, Ames BN. Vitamin K, an example of triage theory: is micronutrient inadequacy linked to diseases of aging. Am J Clin Nutr. 2009 Oct;90(4):889-907. 2009.
• Merli GJ, Fink J. Vitamin K and thrombosis. Vitam Horm 2008;78:265-79. 2008.
• Mizuta T, Ozaki I. Hepatocellular carcinoma and vitamin K. Vitam Horm 2008;78:435-42. 2008.
• Neafsey P. Of blood, bones, and broccoli: warfarin-vitamin K interactions. Home Healthc Nurse 2004 Mar;22(3):178-82; quiz 183-4. 2004.
• Oldenburg J, Marinova M, Muller-Reible C, et al. The vitamin K cycle. Vitam Horm 2008;78:35-62. 2008.
• Pearson DA. Bone health and osteoporosis: the role of vitamin K and potential antagonism by anticoagulants. Nutr Clin Pract 2007 Oct;22(5):517-44. 2007.
• Ryan-Harshman M, Aldoori W. Bone health. New role for vitamin K. Can Fam Physician 2004 Jul;50:993-7. 2004.
• Schurgers LJ, Teunissen KJ, Hamulyak K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. 2007 Apr 15;109(8):3279-83. 2007.
• Shearer MJ, Newman P. Metabolism and cell biology of vitamin K. Thromb Haemost. 2008 Oct;100(4):530-47 2007.
• Tsugawa N, Shiraki M, Suhara Y et al. Vitamin K status of healthy Japanese women: age-related vitamin K requirement for {gamma}-carboxylation of osteocalcin. Am. J. Clinical Nutrition, Feb 2006; 83: 380 - 386. 2006.

Send this page to a friend...