Vitamin K

Definition




Foods highest in vitamin K.





Foods highest in vitamin K.
(bitt24/Shutterstock)

Vitamin K

Age

Adequate intake (mcg/day)

Children 0-6 mos.

2

Children 7-12 mos.

2.5

Children 1-3 yrs.

30

Children 4-8 yrs.

55

Children 9-13 yrs.

60

Children 14-18 yrs.

75

Men 19≥yrs.

120

Women 19≥yrs.

90

Pregnant women 18≤yrs.

75

Breastfeeding women 18≤yrs.

75

Pregnant women 19≥yrs.

90

Breastfeeding women 19≥yrs.

90

Food

Vitamin K (mcg)

Kale, cooked, ½ cup

531

Spinach, cooked, ½ cup

444

Collards, cooked, ½ cup

418

Turnip greens, cooked, ½ cup

264

Spinach, raw, 1 cup

145

Brussels sprouts, cooked, ½ cup

110

Broccoli, cooked, ½ cup

110

Asparagus, 4 spears

30

Grapes, red or green, 1 cup

23

Peas, frozen, cooked, ½ cup

19

Blueberries, ½ cup

14

mcg = microgram

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Vitamin D: Fact Sheet for Health Professionals.” https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional (accessed April 20, 2018).

Purpose

The liver needs vitamin K to make factors that regulate blood clotting. Vitamin K may also play a role in maintaining strong bones and preventing osteoporosis.

Description

Vitamin K is not a single substance but a collection of chemically similar compounds called naphtho-quinones. Vitamin K1, called phylloquinone, is the natural form of vitamin K. It is found in plants and is the main source of vitamin K in the human diet. Vitamin K2 compounds, called menaquinones, are made by bacteria that live in the human intestine. Researchers originally thought that bacteria in the gut provided a substantial percentage of human vitamin K needs, but later research revealed that these bacteria provided only a small amount and that people should get most of their vitamin K from diet. Vitamin K1 is manufactured synthetically and sold under many brand names as a dietary supplement. Vitamin K is also included in many multivitamins. A synthetic water-soluble form of vitamin K called K3 or menadione is not allowed in dietary supplements in the United States because of the risk of serious side effects.

Vitamin K's role in health

Vitamin K is necessary for normal blood clotting (coagulation). In the liver, it is converted into more than half a dozen coenzymes that are essential to the formation of blood clots.

Vitamin K is routinely given to newborns in order to prevent bleeding known as hemorrhagic disease of the newborn (HDN) or vitamin K deficiency bleeding (VKDB), which can occur during the early weeks of life. Although this type of bleeding occurs only in 0.25%–1.7% of untreated newborns, it can be fatal. Since 1961, the American Academy of Pediatrics has recommended that all newborns receive a single 0.5–1.0 mg injection of vitamin K1 immediately after birth. If parents refuse the injection, infants can be given two doses orally (2 mg each). A few researchers have questioned whether this early injection of vitamin K increases the risk of developing childhood cancer; however, a number of well-designed studies have found no link between the two.

There is some evidence that vitamin K may play a role in maintaining strong bones. Certain proteins that regulate the cells (osteoblasts) that deposit calcium and other minerals in bone appear to be dependent on vitamin K. If this is true, vitamin K may play a role in preventing osteoporosis. Definitive evidence has yet to be found, but a list of current and completed clinical trials investigating the use of vitamin K in treating osteoporosis may be found online at ClinicalTrials.gov.

Normal vitamin K requirements

The U.S. Institute of Medicine (IOM) of the National Academy of Sciences develops values called dietary reference intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers: the recommended dietary allowance (RDA), which defines the average daily amount of the nutrient needed to meet the health needs of 97%–98% of the population; adequate intake (AI), an estimate set when there is not enough information to determine an RDA; and tolerable upper intake levels (UL), the average maximum amounts that can be taken daily without risking negative side effects. The DRIs are calculated for children, adults, and pregnant and breastfeeding women.

The following are the AIs for vitamin K for healthy individuals:

Sources of vitamin K

Vitamin K is found in the largest quantities in green, leafy vegetables. Little vitamin K is lost during cooking, but more is lost when foods are frozen. The following list gives the approximate vitamin K1 content of some common foods:

Vitamin K deficiency

Vitamin K deficiency is extremely rare in healthy people. It can, however, occur in individuals who have disorders that interfere with the absorption of nutrients from the intestine. Signs of vitamin K deficiency include easy bruising, excessive bleeding, and slow clotting. People who are at higher risk for vitamin K deficiency include:

KEY TERMS
Clotting factors—
Also known as coagulation factors; proteins in plasma that serve to activate various parts of the blood-clotting process.
Coenzyme—
Also called a cofactor, a small nonprotein molecule that binds to an enzyme and catalyzes (stimulates) enzyme-mediated reactions.
Dietary supplement—
A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.
Enzyme—
A protein that changes the rate of a chemical reaction within the body without being depleted in the reaction.
Fat-soluble vitamin—
A vitamin that dissolves in and can be stored in body fat or the liver.
Osteoporosis—
A condition found in older individuals in which bones decrease in density and become fragile and more likely to break. It can be caused by lack of vitamin D and/or calcium in the diet.
Vitamin—
A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.

Precautions

Injections of vitamin K3 (menadione) are banned in the United States because they can cause liver damage and rupture of red blood cells in infants and children.

People considering taking vitamin K–containing supplements should first consult with their healthcare provider.

Interactions

In addition to interfering with blood-thinning drugs, vitamin K may interact with the following:

Complications

No complications are expected from vitamin K, especially when most of the vitamin K comes from dietary sources. However, pregnant and breastfeeding women should avoid taking vitamin K supplements. In addition, people taking blood-thinning drugs should carefully monitor their intake of vitamin K so that they do not increase the chance of developing blood clots.

QUESTIONS TO ASK YOUR DOCTOR

Parental concerns

Vitamin K deficiency bleeding (VKDB), formerly called hemorrhagic disease of the newborn (HDN), is a bleeding condition seen in some newborns. There are three forms:

Ensuring that newborns receive adequate vitamin K at birth, whether by injection or oral dosage, is the best prevention against VKDB.

See also Dietary supplements ; Osteoporosis diet ; Senior nutrition ; Vitamins .

Resources

BOOKS

Food and Nutrition Board, Institute of Medicine. Report of the Panel on Micronutrients, Subcommittees on Upper Reference Levels of Nutrients and of Interpretation and Uses of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Cooper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001. See esp. Chapter 5, “Vitamin K.” http://books.nap.edu/openbook.php?record_id=10026 (accessed April 23, 2018).

Gaby, Alan R., and Healthnotes, eds. A–Z Guide to Drug-Herb-Vitamin Interactions: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. 2nd ed. New York: Three Rivers Press, 2006.

Zempleni, Janos, et al., eds. Handbook of Vitamins. 5th ed. Boca Raton, FL: Taylor & Francis, 2014.

PERIODICALS

Lippi, Giuseppe, and Massimo Franchini. “Vitamin K in Neonates: Facts and Myths.” Blood Transfusion 9, no. 1 (2011): 4–9. http://dx.crossref.org/10.2450%2F2010.0034-10 (accessed April 23, 2018).

WEBSITES

Canadian Agency for Drugs and Technologies in Health. “Neonatal Vitamin K Administration for the Prevention of Hemorrhagic Disease: A Review of the Clinical Effectiveness, Comparative Effectiveness, and Guidelines.” May 28, 2015. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0078451/ (accessed April 23, 2018).

Drug-Nutrient Interaction Task Force of the National Institutes of Health Clinical Center. “Important Information to Know When You are Taking: Wafarin (Coumadin) and Vitamin K.” National Institutes of Health, September 5, 2012. http://ods.od.nih.gov/pubs/factsheets/coumadin1.pdf (accessed April 23, 2018).

Higdon, Jane, Victoria J. Drake, and Barbara DeLage. “Vitamin K.” Linus Pauling Institute, Oregon State University. http://lpi.oregonstate.edu/mic/vitamins/vitamin-K (accessed April 23, 2018).

MedlinePlus. “Vitamin K.” U.S. National Library of Medicine, National Institutes of Health. https://medlineplus.gov/druginfo/natural/983.html (accessed April 23, 2018).

U.S. Department of Agriculture, National Agricultural Library. “DRI Tables and Application Reports.” Food and Nutrition Information Center. https://www.nal.usda.gov/fnic/dri-tables-and-application-reports (accessed March 15, 2018).

ORGANIZATIONS

Food and Nutrition Information Center, National Agricultural Library, 10301 Baltimore Ave., Rm. 105, Beltsville, MD, 20705, (301) 504-5414, Fax: (301) 504-6409, fnic@ars.usda.gov, http://fnic.nal.usda.gov .

Institute of Medicine, National Academy of Sciences, 500 Fifth St. NW, Washington, DC, 20001, (202) 334-2352, iomwww@nas.edu, http://www.iom.edu .

U.S. Food and Drug Administration, 10903 New Hampshire Ave., Silver Spring, MD, 20993-0002, (888) INFO-FDA (463-6332), http://www.fda.gov .

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.