Cosmic Radiation IS considered to be a serious enough issue to legislate for. There are 2 seperate sections of JAR-OPS 1 that detail exactly what is required of the operator, and the Air Navigation Order was amended a few years ago to take account of monitoring requirements.
Every airline now has (or at least is required to have) a monitoring programme that should highlight high levels of exposure in individuals. Any level of exposure over 6milliSieverts (mSv) per year is considered "high", the average background dose for non-flyers is approximately 2.2mSv per year.
At my company (UK charter airline, crews operating up to 800 flying hours per year), no individual has so far reached the 6mSv figure in 5 years of sampling, although there are some that are above 5mSv.