I do agree with precautionary approach to living in low gravity being the best and farthest conclusion that we can make from the scarce data points gathered so far. Now the best course of action from here would be to test long-term (several months long) effects of low gravity on human body in a specialized mini-station in low Earth orbit. You don't need to build the huge Space Odyssey style rotating structure for this purpose. A single module the size of Destiny lab tethered to a counterweight and spun enough to simulate 1/3 g is all that you need. Sadly nobody from NASA to Zubrin to Musk has serious plans of doing low gravity research before heading to Mars. Maybe an interim step of semi-permanent Lunar base is not such a bad idea even though it would postpone the actual trip to Mars.