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 doesn't 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 colour. 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 deficiency exists, surgeons frequently order vitamin K before an operation to reduce the risk or postoperative bleeding. Some doctors alo 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.

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 litte: 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 prescrbed 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. Brocolli, spring onions and Brussels sprouts are also good sources. Other foods with some vitamin K are pistachio nuts and vegetable oils.


Supplemental vitamin K (more than is found in a multivitamin) shouldbe taken only with your doctor's approval.

Reminder: If you have a medical condition, talk to your doctor before taking supplements.