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Vitamin K Requirements and Dietary Sources

Vitamin Guide

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Updated July 05, 2014

Spinach and vitamin K

Spinach is a great source of vitamin K.

Florin Bleiceanu

Vitamin K is a member of the fat-soluble family of vitamins along with vitamin D, vitamin E and vitamin A. It's essential for normal blood clotting -- in fact the 'K' comes from the German word 'Koagulation' (coagulation).

People who have higher levels of vitamin K in their blood tend to have greater bone density while low levels of vitamin K are associated with osteoporosis. It appears that getting enough vitamin K will also help to keep your bones strong as you age.

Dark green leafy vegetables like spinach and cabbage, cauliflower, broccoli and soybeans are all excellent sources of vitamin K. It's also synthesized by friendly bacteria in your digestive tract.

Your body stores vitamin K in your liver and fat tissue so a deficiency is rare, but it may occur after long-term use of antibiotics or as a result of diseases that harm your digestive tract's ability to absorb nutrients. Symptoms include easy bruising, nosebleeds, bleeding gums, blood in the urine or stool, or extremely heavy menstrual periods. 

The Institute of Medicine sets the daily suggested adequate intakes for vitamins and minerals based on the needs of the average healthy person. The AI for vitamin K varies based on age and gender. The suggested intake doesn't change for women who are pregnant or breastfeeding. If you have any health conditions, you may wish to speak to your doctor about your daily need for vitamin K.

Adequate Intakes

Males

1 to 3 years: 30 micrograms per day
4 to 8 years: 55 micrograms per day
9 to 13 years: 60 micrograms per day
14 to 18 years: 75 micrograms per day
19+ years: 120 micrograms per day

Females

1 to 3 years: 30 micrograms per day
4 to 8 years: 55 micrograms per day
9 to 13 years: 60 micrograms per day
14 to 18 years: 75 micrograms per day
19+ years: 90 micrograms per day

Vitamin K is naturally found in one of four forms:

  • Phylloquinone is the natural version of K1 found in plants and the most common dietary form
  • Phytonadione is a synthetic type of K1
  • Menaquinone, or vitamin K2, is found in animals
  • Menadione, or vitamin K3, is another synthetic form 

Babies born in the U.S. and Canada are given vitamin K shots when they are born because they don't have the right bacteria living in their digestive tracts and breast milk doesn't offer enough vitamin K.

Adults usually don't need vitamin K supplements, but it's often found in multivitamins. Vitamin K supplements should not be taken if you're on certain medications such as blood thinners.

The Institute of Medicine has not been able to determine a tolerable upper level for vitamin K so if you are thinking about taking it as a supplement, please speak with your doctor first.

Sources:

Institute of Medicine of the National Academies. "Dietary Reference Intakes -- Vitamins. Accessed July 4, 2014. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf.

Linus Pauling Institute -- Oregon State University. "Vitamin K." Accessed July 4, 2014. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/.

MedlinePlus. "Vitamin K." http://www.nlm.nih.gov/medlineplus/ency/article/002407.htm.

Otten JJ, Hellwig JP, Meyers LD. "Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." IOM, 2006.

University of Maryland Medical Center. "Vitamin K." Accessed July 4, 2104. http://umm.edu/health/medical/altmed/supplement/vitamin-k.

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