Vitamin K2 synthesized by intestinal bacteria

Vitamin K occurs naturally in two forms.
*Phylloquinone or vitamin K1 (2-methyl-3-phytyl-1,4-naphtoquinone) is synthesized by plants.
*Menaquinones or vitamin K2 (multi-isoprenyl-quinones, several species) are primarily produced by bacteria.

Bacteria synthesize a range of vitamin K forms (but not vitamin K1) using repeating isoprene (5-carbon) units in the side chain of the molecule (vide infra). These forms of vitamin K are designated menaquinone-n (MK-n), where n stands for the number of 5-carbon units in the structure. Menaquinones (MK-n) are collectively referred to as vitamin K2.

Many bacteria that populate the microbial ecosystem of the human intestine synthesize menaquinones, which they utilize as redox reagents in electron transport and oxidative phosphorylation.

Vitamin K is taken in the diet or synthesized by the intestinal bacteria. Its absorption takes place along with fat (chylomicrons) and is dependent on bile salt. Vitamin K is transported along with LDL and is stored mainly in liver and, to a lesser extent, in other tissues.

Menaquinones play important roles in electron transport, oxidative phosphorylation, active transport, and endospore formation in bacteria. In addition to these functions, the variations in the inherent structures of menaquinones and their uneven distributions among bacteria are considered important in bacterial taxonomy.
Vitamin K2 synthesized by intestinal bacteria

Intestinal bacteria produce vitamin K2

There are two sources of this essential vitamin, including vitamin K1, or phylloquinone which is primarily found in green leafy vegetables. Phylloquinone is absorbed in the jejunum and ileum and is primary stored in the liver. The second one is vitamin K2 or menaquinone which is synthesized by certain intestinal bacteria. Menaquinones are absorbed from the distal bowel and stored in the liver.

Specifically, Bacteriodes as well as a few other genera, produce this vitamin. In certain individuals bacteria supply up to 50% of the body’s total vitamin K requirements.

A decrease in dietary of vitamin K2 and/or a reduction in vitamin K2 production by gut bacteria can lower vitamin K levels. Antibiotics can destroy not only harmful digestive tract bacteria, but also the beneficial intestinal bacteria that is needed to create vitamin K.

The primary role of vitamin K in the body is in blood clotting. Vitamin K is also important to bone health. It assists in the mineralization of bone with calcium, thus keeping bones dense and strong.
Intestinal bacteria produce vitamin K2