More vitamin K2, more testosterone
The list of supplements that boost testosterone production has just got a little longer. Nutritionists at Tohoku University in Japan say that male rats synthesise more testosterone if given food that contains high amounts of vitamin K2.
There are two forms of vitamin K: plant-based vitamin K1 [phylloquinone] found in green vegetables such as peas, broccoli and spinach, and the animal-based K2 [menaquinone]. The difference between the two forms is in the 'tail' of prenyl units: K2 has one and K1 doesn't.
The tails vary too: meat and eggs have a tail with four extra prenyl units [MK-4], cheese and quark contain various versions of vitamin K2 with seven, eight and nine prenyl units [MK-7, MK-8 and MK-9]. Fermented products like natto contain a K2 vitamin with seven prenyl units.
We need K2 to enable vital enzymes to function. These include enzymes that synthesise coagulant factors and others that fix calcium in the bones - but vitamin K probably has many more functions. The Japanese research was set up to learn more about these unknown functions of vitamin K2.
The researchers gave one group of lab animals feed containing low amounts of vitamin MK-4 - 0.75 mg per kg - and the other group got food containing high amounts of vitamin MK-4 - 75 mg per kg. The experiment lasted for five weeks.
In the group that got a high amount of MK-4, the animals' testosterone levels and their testicular testosterone concentration increased as the experiment progressed. The vitamin had no effect on the level of LH, the pituitary hormone that stimulates testosterone production in the testes.
The feed with a high vitamin K content caused an increase in the activity of the enzymes PKA and CREB in the testes. This in turn probably caused the enzyme CYP11A to become more active. This enzyme is important for the synthesis of testosterone.
When the researchers repeated their experiment with vitamin K1 they observed hardly any testosterone-boosting effect.
A diet with high levels of vitamin MK-4 "may contribute to the reduced risk of age-related diseases by promoting increased testosterone production in the testis", the researchers write.
The Japanese reveal that they have also done experiments with geranylgeraniol, "a side chain structure of MK-4". This compound and its analogues have been shown to boost testosterone production in cell studies. You can read more about this research here.
Lipids Health Dis. 2011 Sep 13;10:158.
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