http://www.theverge.com/2016/3/1/11138102/scott-kelly-year-i...
I guess they aren't well characterized yet.
Early travelers will face very significant risks. Radiation and zero g are indeed risks, but a minor compared to the other risks.
If you have a 5% of dying in transit or at Mars due to equipment failure, as well as a 2% increased chance of getting cancer at some time in the future, the first obviously is the one to worry about.
