Recommended Nutrient Intakes for Vitamin and Minerals

Vitamin K

Functions

Vitamin K acts primarily in blood clotting. There are at least 13 proteins, as well as  calcium, which are important in making a blood clot. Vitamin K is essential for making at least 4 of these proteins e.g. prothrombin. If a blood clotting factor is lacking hemorrhagic disease results. Thus, if an artery or vein is broken or cut, bleeding goes unchecked.

Vitamin k also participates in the synthesis of a bone protein, osteocalcin. Without vitamin k the bones produce an abnormal protein that cannot bind the minerals that normally form bone.

Recommended Intakes

Table 10: Recommended Intakes for Vitamin K (mg/day)

Food Sources

Vitamin K can be obtained from a nonfood source. Bacteria in the gastrointestinal tract synthesise vitamin K that the body can absorb. However, bacteria synthesis alone is insufficient to meet all of a person's needs.

Vitamin K is present is dark-green vegetables leaves. Good sources include kale, spinach, brussels sprouts, broccoli, parsley, coriander, mint, cabbages and lettuce. Other good sources include beef liver, some vegetable oils, apples, green tea and there is some in cheese.

Deficiency

In vitamin k deficiency there is a bleeding disorder, characterised by low plasma prothrombin activity. Vitamin K deficiency is rare.

Most babies are given an intramuscular vitamin K injection straight after birth to prevent haemorrhagic disease in the newborn. This is because babies are born with a sterile digestive tract and the vitamin K-producing bacteria take weeks to establish themselves in the baby's intestines. Also, vitamin K, like other fat-soluble vitamins, is poorly transported across the placenta from the mother's gut, and human milk usually has a low concentration of vitamin K.

Vitamin K also occurs in patients with malabsorption, and following prolonged use of broad-spectrum antibiotics which can destroy the colonic bacteria. The use of anticoagulant drugs such as warfarin which are given to prevent clotting in the veins, cause vitamin K deficiency.

There are reports of low circulating levels of vitamin K in elderly patients who have fractures, suggesting that suboptimal vitamin K status may play a role in osteoporosis (possibly due to inadequate osteocalcin).

Toxicity

Vitamin K toxicity is uncommon, but can result when vitamin K supplements are prescribed. High does can reduce the effectiveness of anticoagulant drugs used to prevent blood clotting. Toxicity symptoms include red blood cell haemolysis, jaundice, and brain damage.