Fat-Soluble Vitamins; Vitamin K

 Vitamin K

Vitamin K food sources

Vitamin K appropriately gets its name from the Danish word koagulation ("coagulation" or "clotting"). Its primary action s blood clotting, in which its presence can make the difference between life and death. Blood has a remarkable ability to remain liquid, but it can clot within seconds when the integrity of that system is distributed. It has other names such as Phylloquinone (vitamin K1), menaquinone (vitamin K2), and menadione (in supplements).

Roles in the Body:

More than a dozen different proteins and the mineral calcium are involved in making a blood clot. Vitamin K is essential for the activation of several of these proteins, among them prothrombin, made by the liver as a precursor of the protein thrombin. When any of the blood-clotting factors is lacking, hemorrhagic disease results. If an artery or vein is cut or broken, bleeding goes unchecked. Of course, this is not say that hemorrhaging is always caused by vitamin K deficiency. Another cause is the genetic disorder hemophilia, which is neither caused nor cured by vitamin K. Soon after birth, newborn infants receive a dose of vitamin K to prevent hemorrhagic disease.

Vitamin K also participates in the metabolism of bone proteins, most notably osteocalcin. Without vitamin K, osteocalcin cannot bind to the minerals of vitamin K helps decrease bone turnover and protect against fractures. The effectiveness of vitamin K supplements on bone health is inconclusive.

Vitamin K is historically known for its role in blood clotting, and more recently for its participation in bone building, but additional roles continue to be discovered. Recent research suggests that vitamin K may be associated with a reduced risk of heart disease, some cancers, and all-cause mortality. 

Vitamin K Recommendation & Sources:

Like vitamin D, vitamin K can be obtained both from foods and from a nonfood source. Bacteria in the GI tract synthesize vitamin K, although the amount is insufficient to meet the body's needs and its bioavailability is limited. Therefore the diet must also supply vitamin K, which is found primarily in leafy green vegetables such as spinach, cabbage, collards, brussels sprouts and kale, fruits such as avocado and kiwi, and some vegetable oils such as soybean oil and canola oil. Naturally occurring vitamin K in foods is phylloquinone (sometimes called vitamin K1), whereas vitamin K produced by GI bacteria is menaquinone (sometimes called vitamin K2).

Vitamin K Deficiency:

A primary deficiency develops in response to an inadequate dietary intake whereas a secondary deficiency occurs for other reasons. A primary deficiency of vitamin K is rare, but a secondary deficiency may occur in two circumstances. First, whenever fat absorption falters, as occurs when bile production fails, vitamin K absorption diminishes. Second, some drugs disrupt vitamin K's synthesis and action in the body: antibiotics kill the vitamin K-producing bacteria in the intestine, and anticoagulant drugs interfere with vitamin K metabolism and activity. Excessive bleeding due to a vitamin K deficiency can be fatal.

Newborn infants present a unique case of vitamin K nutrition because they are born with a sterile intestinal tract, and the vitamin K-producing bacteria take weeks to establish themselves. Furthermore, vitamin K is minimally transported across the placenta and its concentration in breast milk is low. At the same time, plasma prothrombin concentrations are low, which reduces the likelihood of fatal blood clotting during the stress of birth. To prevent hemorrhagic disease in the newborn, a single dose of vitamin K is given at birth by intramuscular injection. Concerns that vitamin K given at birth raises the risks of childhood cancer are unfounded.

Vitamin K Toxicity:

Toxicity is not common, and no adverse effects have been reported with high intakes of vitamin K. Therefore, a UL has not been established. High doses of vitamin K can, however, reduces the effectiveness of anticoagulant drugs used to prevent blood clotting. People taking these drugs should try to eat the same amount of vitamin K-rich foods daily; unfortunately, many avoid eating green vegetables instead, which results in low vitamin K intakes. Their blood clotting times should be monitored regularly and drug dosages adjusted accordingly.