Researchers from Japan had found in a previous study that vitamin K influenced expression of genes in the tested that are involved in production of testosterone.
Therefore, they now investigated if vitamin K administration in testes cell lines or living rats would influence testosterone levels.
Vitamin K can be divided in two types of naturally-occurring vitamin K molecules:
- phylloquinone (vitamin K1)
- menaquinones (vitamin K2)
Vitamin K1 can be found in green vegetables, whereas Vitamin K2 is mainly produced by microorganisms.
The researchers found that Menaquinone-4 (MK-4), an analogue of vitamin k2, increased testosterone when they administrated it to the testes cell line. Interestingly, administration of vitamin K1 had no effect on testosterone. This can be seen in the figure below.
When they put MK-4 in the food of rats, the testosterone levels of the rats also increased. This can be seen in the figure below.
The researchers tried to figure out the mechanism of how MK-4 boosts testosterone levels.
Luteinizing hormone, a hormone secreted in the brain that signals the testes to increase testosterone production, was not affected.
But they observed that MK-4 administration had elevated the levels of CPA11A in the testes. CPA11 is an enzyme that catalyzes the conversion of cholesterol to testosterone in testes, the rate limiting step in testosterone production.
Thus, MK-4 appears works directly on the testes to boost testosterone.