[voxic11]

Your first link says the mechanism is unknown right in the beginning. Third link doesn't mention mechanisms at all. Only the second link attempts some guesses. But it still concludes that "It is beyond the scope of this paper to test the exact mechanism, so we leave it as agenda for future research."

[tlb]

Typically, knowing the mechanism comes long after solid evidence of the effect.

The mechanisms by which cigarettes cause lung cancer are surprisingly complex and weren't fully understood for a long time, but it's obvious that some kind of mechanism is plausible.

So usually the bar for taking something seriously is: statistical evidence of a significant harmful effect, and at least one plausible hypothesis for a mechanism. But you don't have to be sure of the mechanism.