Vitamin K

Vitamin K is a group of structurally similar, fat-soluble vitamins that are needed for the posttranslational modification of certain proteins required for blood coagulation and in metabolic pathways in bone and other tissue. They are 2-methyl-1,4-naphthoquinone (3-) derivatives. This group of vitamins includes two natural vitamers: vitamin K₁ and vitamin K_2.^[1] The three basic forms of Vitamin K are K1, K2, and K3.^[2]

Vitamin K₁, also known as phylloquinone or phytomenadione (also called phytonadione), is synthesized by plants, and is found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis.

Three synthetic types of vitamin K are known: vitamins K₃, K₄, and K₅.

Although the natural K₁ and K₂ forms are nontoxic, the synthetic form K_3(menadione) has shown toxicity.^[3]

Vitamin K_2 (MK4, but not MK7 or vitamin K₁) has also been shown to prevent bone loss and/or fractures in the following circumstances:

• caused by corticosteroids (e.g., prednisone, dexamethasone, prednisolone),^{[17][18][19][20]}
• anorexia nervosa,^[21]
• cirrhosis of the liver,^[22]
• postmenopausal osteoporosis,^{[16][23][24][25][26][27]}
• disuse from stroke,^[28]
• Alzheimer's disease,^[29]
• Parkinson disease,^[30]
• primary biliary cirrhosis^[31]
• and leuprolide treatment (for prostate cancer).^[32]

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