Vitamin K2 and Testosterone: The Human vs. Animal Evidence Gap
“Vitamin K2 boosts testosterone” shows up in enough testosterone supplement marketing that it reads like settled science. It isn’t. We traced the specific research behind this claim, and it comes from exactly one study — conducted in rats and cultured cells, never in a human being.
What Vitamin K2 Is
Vitamin K2 (menaquinone) is a fat-soluble vitamin most established for its role in bone health and blood clotting, working alongside vitamin D3 in many supplement formulas for that reason. It comes in several forms — MK-4 and MK-7 are the two most common in supplements. The testosterone claim specifically traces back to research on MK-4.
The Study Behind the Claim
This is the actual, complete source behind the “Vitamin K2 boosts testosterone” claim as it’s commonly used in supplement marketing. It’s a real, published, peer-reviewed study — but every measurement was taken in rats or in cultured rat tumor cells. No part of this research involved human subjects.
The Proposed Mechanism
The researchers found that MK-4 activates an enzyme pathway (protein kinase A, leading to increased expression of CYP11A1, a rate-limiting enzyme in testosterone synthesis) without changing luteinizing hormone (LH) levels — suggesting a potential direct effect on testicular tissue rather than working through the brain’s usual hormone signaling. This is a genuinely interesting, plausible biological mechanism. It’s also, again, based entirely on rat and cell-culture data.
What’s Missing
No Human Trials Found
We could not find a single published human trial testing whether Vitamin K2 supplementation raises testosterone in men. Even sources that promote K2 for this purpose acknowledge the gap directly — one health-clinic blog citing this exact study concluded “more human studies are necessary” before drawing conclusions about men’s testosterone or sexual health.
This doesn’t mean the animal finding is meaningless — early-stage animal research is a normal, legitimate part of how nutrition science progresses. It means the confident, human-outcome-implying way this claim often gets marketed isn’t supported by the evidence that actually exists yet.
Where This Shows Up
We found Vitamin K2 in two testosterone products we’ve reviewed: TestoFuel, whose marketing cites this exact rat study while presenting it as a “70% increase in circulating testosterone levels” without clarifying it wasn’t tested in humans, and Testogen Ultimate, which discloses 90mcg of K2 (as MK-7, a different form than the one studied) without making a testosterone-specific claim from it.
FAQ
Does Vitamin K2 raise testosterone in men?
There’s no published human trial testing this directly. The claim traces to a single study in rats and cultured rat cells, which is real and peer-reviewed, but doesn’t establish an effect in humans.
Is Vitamin K2 still worth taking?
It has real, separate, better-established evidence for bone health, typically alongside vitamin D3. That’s a different claim than the testosterone one covered here.
Which K2 form was studied?
MK-4 specifically. Many commercial supplements use MK-7, a different form with its own separate research on bone and cardiovascular health, not tested for this testosterone claim.
See how this fits into our full product score
Read Our TestoFuel ReviewLast reviewed: September 2026 · Read our full rating methodology · Clinical reference: Ito et al., 2011, Lipids in Health and Disease.