Some papers on the subject.
https://ntrs.nasa.gov/archive/nasa/c...0070028831.pdf
https://oem.bmj.com/content/59/7/428
Extracts from the latter,
In assessing risks, it is important to remember that extrapolations are only as good as their underlying assumptions. Little is known of the radiobiological effects of low dose ionising radiation, much less that of low dose ionising radiation of the type and quantity which airline pilots and cabin crew are exposed to at altitude. A great deal of what we assume is therefore inferred by extrapolating from experience with high doses.
Here, there are good grounds to think that the health risk of exposure to cosmic radiation is not zero. We know, for instance, that radiation mutagenesis principally proceeds through DNA deletions, and misrepair and misrecombination at DNA double stranded breaks. We also know that a single track of low energy ionising radiation can produce a double stranded break in the DNA of a single cell nucleus. A study of astronauts on a 4 month mission to the Mir space station (dosage received: 147.5 mSv) has shown significantly increased frequency of chromosomal aberrations after the flight, compared with samples obtained before the flight. A significant increase in chromosomal aberrations has also been found in Concorde pilots compared with controls, and indeed the same has been found in civilian pilots and cabin crew of subsonic aircraft.
Even more worrying is the discovery in 1992 of a previously unknown pathway termed “radiation induced genomic instability”, by which radiation can subvert living cells. It was previously thought that when ionising radiation hits a living cell and damages its DNA, only when the damage is not satisfactorily repaired is it passed on to the daughter cells; now, repeated experiments in vitro and in vivo have shown that radiation can additionally inflict damage that shows up only after several generations of cell division. This is particularly worrying as it raises the spectre of delayed genetic effects on the gene pool of future generations.