Biological Role of Vitamin K

The Vitamin K Epoxide Cycle

Dietary Intakes in Older infants, Children, and Adults

(a) The number of subjects are stratified by age and/or sex
(b) Total diet study (c) Recommended Dietary Allowance

Dietary intakes in older infants, children, and adults and their adequacy

The only comprehensive national survey of phylloquinone intakes across all age groups (except infants aged 0–6 months) is that of the US Food and Drug Administration Total Diet Study, which was based on the 1987–88 Nationwide Food Consumption Survey. For infants and children from the age of 6 months to 16 years, average phylloquinone intakes were above the current US recommended dietary allowance (RDA) values for their respective age groups, more so for children up to 10 years than from 10 to 16 years. There have been no studies of intakes in children in relation to functional markers of vitamin K sufficiency in children.

Dietary Intake in Infants and Their Adequacy

The average intake of phylloquinone in infants fed human milk during the first 6 months of life has been reported to be less than 1 μg/day; this is approximately 100-fold lower than the intake in infants fed a typical supplemented formula. This big disparity between intakes is reflected in plasma levels.

Using the detection of PIVKA-II as a marker of sub-clinical deficiency, a study from Germany concluded that a minimum daily intake of about 100 ml of colostral milk (that supplies about 0.2-0.3 μg of phylloquinone) is sufficient for normal haemostasis in a baby of about 3 kg during the first week of life. Similar conclusions were reached in a Japanese study which showed a linear correlation between the prevalence of PIVKA-II and the volume of breast milk ingested over 3 days; 95 percent of infants with detectable PIVKA-II had average daily intakes of less than about 120 ml, but the marker was not detectable when intakes reached 170 ml/day.

Bio-availability of Vitamin K from Foods

Very little is known about the bio-availability of the K vitamins from different foods. It has been estimated that the efficiency of absorption of phylloquinone from boiled spinach (eaten with butter) is no greater than 10 percent compared with an estimated 80 percent when phylloquinone is given in its free form. This poor absorption of phylloquinone from green leafy vegetables may be explained by its location in chloroplasts and tight association with the thylakoid membrane, where this naphthoquinone plays a role in photosynthesis. In comparison, the bio-availability of MK-4 from butter artificially enriched with this vitamer was more than twofold higher than that of phylloquinone from spinach. 

Vitamin K Dietary Sources

High-performance liquid chromatography can be used to accurately determine the major dietary form of vitamin K (phylloquinone) in foods, and food tables are being compiled for Western diets. Phylloquinone is distributed ubiquitously throughout the diet, and the range of concentrations in different food categories is very wide. In general, the relative values in vegetables confirm the known association of phylloquinone with photosynthetic tissues, with the highest values (normally in the range 400–700 μg/100 g) being found in green leafy vegetables. 

Population at Risk for Vitamin K Deficiency

Vitamin K deficiency bleeding in infants

In infants up to around age 6 months, vitamin K deficiency, although rare, represents a significant public health problem throughout the world. The deficiency syndrome is traditionally known as haemorrhagic disease of the newborn or more recently, to give a better definition of the cause, vitamin K deficiency bleeding (VKDB).

Vitamin K Overview of Metabolism

Absorption and transport

Dietary vitamin K, mainly as phylloquinone, is absorbed chemically unchanged from the proximal intestine after solubilisation into mixed micelles composed of bile salts and the products of pancreatic lipolysis. In healthy adults the efficiency of absorption of phylloquinone in its free form is about 80 percent. Within the intestinal mucosa the vitamin is incorporated into chylomicrons, is secreted into the lymph, and enters the blood via the lacteals. Once in the circulation, phylloquinone is rapidly cleared at a rate consistent with its continuing association with chylomicrons and the chylomicron remnants which are produced by lipoprotein lipase hydrolysis at the surface of capillary endothelial cells.