I would be very surprised if the research you’re pointing to suggests causation. I’m not saying causation doesn’t exist. But the reason why this issue is hard

I would be very surprised if the research you’re pointing to suggests causation. I’m not saying causation doesn’t exist. But the reason why this issue is hard to resolve is precisely because causation one way or another is hard to establish. Causation for specific effects of Sun exposure is much easier to establish (for example skin cancer due to exposure, or lower depression due to exposure).