menadione

Menadione, also known as vitamin K3, is a synthetic form of vitamin K. Its chemical name is 2-methyl-1,4-naphthoquinone. It is related to the natural vitamin K compounds phylloquinone (K1) and menaquinones (K2), but it is not produced by plants or gut bacteria in significant amounts and is manufactured industrially as a standalone compound. In humans, menadione provides very limited vitamin K activity and is not considered a reliable dietary source.

Biochemically, vitamin K functions as a cofactor for the enzyme gamma-glutamyl carboxylase, enabling the carboxylation of specific glutamate residues in blood-clotting factors II, VII, IX, and X and in proteins C and S. Menadione can be reduced to hydroquinone forms that enter the vitamin K cycle, but its efficiency is low and it is also known to undergo redox cycling that can generate reactive oxygen species, giving it potential pro-oxidant properties.

Uses and regulation: In the past, menadione was used as a feed additive in animal nutrition to supply vitamin K activity. In human medicine and self-supplementation, its use has diminished due to safety concerns. High-dose exposure has been associated with oxidative stress, hemolysis, liver injury, and methemoglobinemia; neonates are at particular risk. Consequently, many regulatory agencies restrict or prohibit its use as a dietary supplement for humans, and it is generally avoided in human nutrition.

History: Menadione was developed in the early 20th century as a synthetic vitamin K analogue. It is one of several vitamers, but unlike K1 and K2 it is not an essential nutrient for humans.