IMO, there is a statistical increase of risk from harm by radiation at increasing dosage. However, the harm done may not show itself for decades, the percentage of current professional aviators who display symptoms is low-ish and there is never (in the case of long term background level increase) any specific evidence that any particular radiation dose caused a specific harm. Notwithstanding this, radiation damage does occur but, again IMO, regulating authorities and employers have long colluded in downplaying the damage risk.
OAP