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Vitamin K

Doctors have long used vitamin K, which promotes blood clotting, to help heal incisions in surgical patients and to prevent bleeding problems in newborns.  This vitamin also helps to build strong bones and may be useful for combating the threat of osteoporosis.

What it is?

In the 1930s Danish researchers noted that baby chickens fed a fat-free diet developed bleeding problems.  The problem was solved with an alfalfa-based compound that was named vitamin K, for Koagulation.  Scientists now know that most of the body's vitamin K needs are met by bacteria in the intestines that produce this vitamin, and only about 20% comes from foods.  Deficiencies are rare in healthy people, even though the body does'nt store vitamin K in large amounts.  Natural forms of vitamin K come from chlorophyll – the same substance that gives plants such as alfalfa their green color.  Synthetic supplements are also available on prescription.  Other names for vitamin K are phytonadione and menadione.

What it does?

This single nutrient sets in motion the entire blood-clotting process as soon as a wound occurs.  Without it, we might bleed to death.  Researchers have discovered that vitamin K helps to protect bone health as well.


Doctors often recommend preventive doses of vitamin K if bleeding or haemorrhaging is a concern.  Even when no deficiencu exists, surgeons frequently order vitamin K before an operation to reduce the risk of postoperative bleeding.  Some doctors also prescribe it for excessive menstrual bleeding.  Though not yet a widely accepted treatment, vitamin K may provide great benefits for those suffering from osteoporosis.  Some studies show that it helps the body to make use of calcium and decreases the risk of fractures.  Vitamin K may be especially important for bone health in older women.  Not surprisingly, it is included among the ingredients in some bone-building formulas.

Additional Benefits

Vitamin K may play a role in preventing cancer and help those undergoing radiotherapy.  Recent findings also put vitamin K in the arsenal of heart-smart nutrients.  Some evidence suggests that it may halt the build-up of disease-causing plaque in arteries and reduce the blood level of LDL ('bad') cholesterol.  But more research is needed to define the role of vitamin K in these and other disorders.

Common Uses

  • Reduces the risk of internal haemorrhaging.
  • Protects against bleeding problems after surgery.
  • Helps to build strong bones and ward off or treat osteoporosis.


  • Tablet.
  • Liquid.


  • Supplemental vitamin K (more than is found `in multivitamin should be taken only with your doctor's approval.
  • Reminder:  If you have a medical condition, talk to your doctor before taking supplements.

How much you need?

Because vitamin K needs are met by the body, there is no RDI in Australia or New Zealand.

If you get too little:

In healthy people, a vitamin K deficiency is rare, because the body manufactures most of what it requires.  In fact, deficiencies are found only in those with liver disease or intestinal illnesses that interfere with fat absorption.  However, vitamin K levels can fall as a result of using antibiotics long term.  One of the first signs of a deficiency is a tendency to bruise easily.  Those at risk need careful medical monitoring because they could bleed to death in the event of a serious injury.

If you get too much:

It's hard to get too much vitamin K because it's not abundant in any one food (except leafy greens).  Although even megadoses are not toxic, high doses can be dangerous if you're taking anticoagulants.  Large doses also may cause flushing and sweating.

How to take it?


This vitamin is rarely included in multivitamins sold in Australia and New Zealand.  Bone-building formulas may provide around 300 mcg a day – the equivalent of adding a large leafy salad to your daily diet.  Higher doses (such as those in multivitamins formulated for prenatal use) may be prescribed under medical supervision for those with specific medical needs.

Guidelines for use:

When prescribed, vitamin K should be taken with meals to enhance absorption.

Other Sources

Leafy green vegetables, including – per cup of vegetable – kale (547 mcg), silverbeet (299 mcg) and turnip greens (138 mcg), are richest in vitamin K.  Broccoli, spring onions and Brussels sprouts are also good sources.  Other foods with some vitamin K are pistachio nuts and vegetable oils.

Facts and Tips

  • If you take blood-thinning medications and eat lots of leafy green vegetables, which are rich in vitamin K, let your doctor know.  Your medication dose may need to be adjusted.
  • Vitamin E helps the body to use vitamin E – more than 1000 IU a day – taken long term may impair vitamin K function and increase your risk of bleeding.

Latest Findings

Green tea is sometimes considered the leading source of vitamin K: it has 1700 mcg in 225 g.  Many doctors consequently advise people on anticoagulants (blood thinners) not to drink it.  In fact, that's the amount of vitamin K in 225 g of tea leaves – which would make hundreds of cups of brewed tea.  According to a study from Tufts University in Boston, one cup of green tea contains virtually no vitamin K.