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Vitamins & minerals health centre

Vitamin K

Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding and helping wounds to heal.

Vitamin K uses

Low levels of vitamin K can increase the risk of uncontrolled bleeding. While vitamin K deficiencies are rare in adults, they are very common in newborn infants. A single dose of vitamin K given to newborns is standard. Vitamin K is also used to counteract an overdose of the blood thinner warfarin.

While vitamin K deficiencies are uncommon, you may be at higher risk if you:

  • Have a disease that affects absorption in the digestive tract, such as Crohn's disease or ulcerative colitis
  • Take medications that interfere with vitamin K absorption
  • Are severely malnourished
  • Drink large amounts of alcohol

In these cases, your GP may suggest vitamin K supplements.

Some studies suggest vitamin K may help stop bone loss from osteoporosis. However, it's not clear that supplements will help people with osteoporosis who don't also have a vitamin K deficiency and more research is needed. Other traditional uses of vitamin K, such as for cancer sufferers, for the symptoms of morning sickness, for the removal of spider veins and for other conditions, are unproven.

Vitamin K dose and instructions for use

The NHS says adults need approximately 0.001mg a day of vitamin K for each kilo of body weight.

Vitamin K food sources

Good natural food sources of vitamin K include:

  • Vegetables like spinach and broccoli
  • Vegetable oils
  • Cereals

Vitamin K supplement information

Vitamin K is available in oral and topical forms. Injectable vitamin K is only available by prescription.

Like any supplement, keep vitamin K supplements in a cool, dry place, away from humidity and direct sunlight.

Vitamin K warnings

  • Side effects of vitamin K include upset stomach. At higher doses, vitamin K may trigger allergic reactions.
  • Interactions. Many medications can interfere with the effects of vitamin K. They include antacids, blood thinners, antibiotics, aspirin and drugs for cancer, seizures, high cholesterol and other conditions.
  • Risks. People using warfarin for heart problems, clotting disorders or other conditions may need to change their diets to control the amount of vitamin K they take in.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on September 03, 2015

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