You don't risk dying from radiation if that's what you mean, but 2-3 days of eating crap food and drinking cheap champagne isn't any good for you. The recycled air isn't ideal either, especially if you're flying old 777-200s or their contemporaries with dry air which I know is more likely to give me some kind of cold at the end of a lot of flying.
Also don't underestimate the confusion the body will go through being denied the usual morning and nighttime cues.
Yes I guess that's part of what I mean, the radiation is one tiny part.
But I guess the amount of time being up in the air and the stress it puts on the body what with the cabin altitude, drinking and just sitting for hours on end.