'No proven link' is a phrase that I find a bit of an ugly beast.
It can be a bit like having a conversation where someone constantly goes 'Well prove it then' in a passive aggressive manner, often knowing full well that it's not something that could be reasonably proved.
That doesn't mean something can also be disproved either though.
This is where understanding the principles of research are important.
If memory serves I think Ben Goldacre talks about this when he talks about bad science.
It never fails to surprise how many scientists don't understand this and more generally how few people really know the difference between causation and correlation.
The point for me is there are explicit and clear questions that arise out of what we do know, but no one is adequately able to either prove nor disprove the theories at this stage. And no one has yet explored these questions fully
It's true that there are somethings we can not definitely prove nor disprove, but we make a judgement on the balance of the evidence available to us. But we are certainly not at this point yet, as there are lots of avenues (questions) that we know about that haven't been properly explored.
If anything, on the balance of what we do know, the advice should be to urge caution precisely because there does seem to be a correlation we haven't fully explained. Cos that's what you do in the absence of knowledge.
At the moment the position is there is some evidence which points us in the direction of a correlation which is unexplained, we should therefore proceed with caution, bearing it in mind and asking the question throughout the process.
The problem comes when you are told you can't ask that question. That's ideological interference.
And as ever safeguarding principles always come first. And safeguarding requires constant asking of questions.