Twice Today, I heard about Sharipov's size issue (french radio and TV and nowhere else).
Everyone in space grows, but the russians have an outfit they're supposed to wear and it puts pressure ( and it's not confortable:-/) on their shoulders in order to compress their spine.
Bones in 0G loose calcium and one wonders what effect it has (bones breaking more easily) if not taken care of.

There's also the 4 months threshold (maybe that's why NASA doesn't want astronauts to spend too long a time in space).
The russians have noticed that cosmonauts, after 4 or 6 months in space, have a tendency to be less attentive, to not follow requests as thoroughly as earlier. Many cosmonauts could be efficient until the 6th month, but longer than that did increase risks (if only because of lack of attention).
There is still plenty to learn before the big jump to the nearest planet.

Raoul