Low gravity will always have health effects. If you plan on returning to the Earth and have a very short stay, 0.5 G is probably a massive improvement over 1 G,

Low gravity will always have health effects. If you plan on returning to the Earth and have a very short stay, 0.5 G is probably a massive improvement over 1 G, especially if you keep doing exercise. For a martian transfer, you'd acutally only need 0.38 G as they'll be losing their bone structure to Martian gravity either way. Funny thing actually, a person born on Mars could probably never walk on the Earth without years of intensive physiotherapy.