Vitamin K has gotten a lot of press in recent years. This once little-known vitamin is really racking up the clinical studies that show just how critical it is. What’s known is that vitamin K plays a critical role in enabling certain enzymes in the body to function. For example, some of these enzymes help to form blood clotting factors that allow blood to clot, which is essential to stop from bleeding to death. Other enzymes are important for fixing calcium in bones. Beyond that, research has even found that vitamin K may be critical for testosterone production.
Before I get into the research on vitamin K and testosterone, there are a few things you need to know about the different forms of vitamin K. There are two major forms you need to be familiar with: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). K1 is the plant form of vitamin K and is found in green veggies, like spinach and broccoli. K2 is the animal form and is found in dairy, meat, organ meat and eggs, as well as bacteria. The difference between the two forms is that K2 has sort of a chemical tail or side chain. This tail makes all the difference, as does its length. In fact, there are different forms of menaquinone and they all differ in the length of their tail.
The K2 found in egg yolks and meat (especially chicken) and cheddar cheese is called MK-4. This is the form that we and other animals use mainly in our bodies, and we convert the K1 from plant into MK-4. Other forms go form MK-5 to MK-14 and these are all formed by bacteria.
In one study, Japanese researchers gave one group of rats a diet low in MK-4 and another group a diet supplemented with MK-4 for 5 weeks. They reported in a 2011 issue of the journal Lipids in Health and Disease that the mice getting the supplemental MK-4 increased their testosterone levels by about twice that of the rats on the low MK-4. They discovered that the MK-4 activated enzymes in the testicles of the rats are critical for testosterone production. When they repeated the same experiment using vitamin K1, there was no increase in testosterone levels.
Jim’s Take-Home Point:
Yes, this study was done in rats. However, I have a lot of experience using rats in research, back to when I was at Yale University School of Medicine. There’s a reason we use rats: A lot of their physiological systems are similar to ours. Humans have the same enzymes that rats do in the testicles that convert cholesterol into testosterone. So, although this study needs to be done in humans to be completely sure, I feel very confident that MK-4 has a similar effect in men. This is why MK-4 is one of the vitamin K2 forms in my multivitamin Vita JYM.
Another good way to get MK-4 directly is to eat egg yolks – yet another reason why I generally recommend eating whole eggs instead of just egg whites. The darker the yolk, the more MK-4 it contains, so try your best to get free-range eggs, which have darker yolks than conventional eggs.
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