Forgive me as a Nigel from butting in but be wary of focusing on radiation scare stories .......( BTW thanks for the link jet2..).
Yes, radiation levels at altitude are elevated compared with what you (generally) get at ground level but the dose rates ( roughly speaking the amount of radiation absorbed per second) you get when flying are very low when compared with chest X-rays and msri scans. Comparing cosmic radiation and medical radiation is in many ways like comparing apples and oranges, it's not a valid or sensible comparison. The effect of cosmic radiation on health is so small that it's effect, if any, is buried by ill health due to other causes. Furthermore it's somewhat ironic that many crew members who claim to be concerned about cosmic radiation will still quite happily fly to the tropics and then either throw themselves onto a sunlounger for hours on end or play a round of golf without sunblock or hat...now that "cosmic" radiation (UV) is shown and known to be extremely damaging and can have fatal effects.
IMHO the phenomonem we really do need to concern ourselves with are:
Infrequent/irregular exposure to sunlight
Poor diets, irregular eating habits, dehydration.
Irregular sleep patterns, time zone changes , Fatigue......