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Vitamins, Minerals and Dietary Supplements

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Vitamin K

What is vitamin K?

Vitamin K is a fat-soluble vitamin stored in the liver and the body's fat reserves. It is one of two naturally occurring vitamins in the body and is produced by bacteria that line the gastrointestinal tract.

Why do we need it?

Vitamin K's most important role is in making many of the proteins responsible for blood clotting. It also helps produce a protein called osteocalcin, which plays a crucial role in maintaining healthy bones, healing fractures and preventing osteoporosis. Some studies indicate that it helps in maintaining strong bones in the elderly.

How much vitamin K should I take?

According to the National Academy of Sciences, the recommended daily allowance (RDA) for vitamin K is as follows:

  • Adult men: 80 micrograms/day
  • Adult women: 65 micrograms/day
  • Children aged 7-10: 30 micrograms/day
  • Infants: 10 micrograms/day
  • Pregnant/lactating women: 65 micrograms/day

What are some good sources of vitamin K?

Canola oil, soybean oil, and green, leafy vegetables (such as spinach, broccoli, cabbage and turnip greens) are the best sources of vitamin K. It can also be found in milk, eggs, beef liver, bran and citrus fruits.

What can happen if I don't get enough vitamin K?

Because vitamin K is a naturally occurring substance (it is produced by bacteria in the intestines and stored in the liver), deficiency is very uncommon. However, deficiency may occur in people who have trouble absorbing fats, are on long-term antibiotic therapy, or take other medications such as warfarin and phenobarbital. Symptoms of vitamin K deficiency include easy bruising and ruptured capillaries. A low intake of vitamin K may also increase the risk of hip fractures in women.

What can happen if I take too much?

Allergic-type reactions, including skin rashes and itching, have been reported in individuals taking high doses of vitamin K. People taking an anticoagulant called coumadin (also known as warfarin) should not take vitamin K supplements without first consulting a physician.

References

  • Garrison R, Somer E. The Nutrition Desk Reference. New Canaan, CN: Keats Publishing, 1995.
  • Hendler S. The Doctor's Vitamin and Mineral Encyclopedia. New York: Simon & Schuster, 1990.
  • Janson M. The Vitamin Revolution. Greenville, NH: Arcadia Press, 1996.
  • Murray M. Encyclopedia of Natural Medicine, 2nd ed. Rocklin, CA: Prima Publishing, 1998.
  • Murray M. Encyclopedia of Nutritional Supplements. Rocklin, CA: Prima Publishing, 1996.
  • Recommended Dietary Allowances, 10th ed. Washington, D.C.: National Academy Press, 1989.

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