Subtypes of Vitamin K2
Vitamin K2 (menaquinone) includes several subtypes; two subtypes most studied are menaquinone-4 (menatetrenone, MK4) and menaquinone-7 (MK7).
MK4 is produced via conversion of vitamin K1 in the testes, pancreas and arterial walls. While major questions still surround the biochemical pathway for the transformation of vitamin K1 to MK4, studies demonstrate the conversion is not dependent on gut bacteria, as it occurs in germ-free rats and in parenterally-administered K1 in rats. In fact, tissues that accumulate high amounts of MK4 have a remarkable capacity to convert up to 90% of the available K1 into MK4.
Menaquinone-7 (MK7) is different from MK4 in that it is not produced by human tissue. MK7 consumption has been shown to reduce the risk of bone fractures and cardiovascular disorders that are crucial health issues worldwide. There is a need for production of concentrated, supplementary MK7 in the diet. Recently, leading research teams from Australia, Japan and Korea are broadening the understandings on MK7 and its production. It has been reported that MK7 may be converted from phylloquinone (K1) in the colon by E-coli bacteria. However, bacteria-derived menaquinones (MK7) appear to contribute minimally to overall vitamin K status. MK4 and MK7 are both found in the United States in dietary supplements for bone health.
The US FDA has not approved any form of vitamin K for the prevention or treatment of osteoporosis; however, MK4 has been shown to decrease fractures up to 87%. In the amount of 45 mg daily MK4 has been approved by the Ministry of Health in Japan since 1995 for the prevention and treatment of osteoporosis.
Vitamin K2 (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),
- anorexia nervosa,
- cirrhosis of the liver,
- postmenopausal osteoporosis,
- disuse from stroke,
- Alzheimer's disease,
- Parkinson disease,
- primary biliary cirrhosis
- and leuprolide treatment (for prostate cancer).
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