[gpm]

That shows health effects (which we already know exist) - why does it support the claim that the human body is unlikely to reach mars?

My understanding is that without shielding about 5% of the voyagers will get cancer, and that many people consider this a reasonably acceptable risk. Does this make that number substantially worse?

[plopilop]

It's also affecting nutrient absorption. I don't see any quantitative number about this in the paper but it's been mentioned several time as having an impact.