What is the minimum gravity needed to keep astronauts healthy?

We posed this question to Dr. Kevin Fong, Co-Director of the Centre of Aviation Space and Extreme Environment Medicine...

Kevin - That's an excellent question and the answer is probably. The problem with long duration space flight is that microgravity has a range of very negative consequences for the human body over extended durations and we're talking about going to Mars, missions that may be up to a thousand days in microgravity or only partial gravity. The big question is, how do you protect astronauts during that time and you've got two options - either you go quickly and reduce the exposure to microgravity or you put up with a long duration stay in space and you introduce a counter measure, and that counter measure should be artificial gravity. They've experimented with what might be the best prescription for gravity. You can think of gravity like a drug. certainly on Earth, we are not constantly exposed to an unchanging 1 G environment when you run up and down a flight of stairs, you shock load your joints, and you get more than one G loading at load bearing areas during exercise or impact. When you're asleep and you're lying horizontally on your beds along the vertical axis, your body is essentially perpendicular to the gravitational field and so is gravitationally unloaded. And indeed, that's how we simulate microgravity here on Earth, we put people in bed and tilt them 6 degrees head down. So what is the dose of gravity that would work? I was involved in a pilot study that suggested that if you lay someone down on a short arm centrifuge, and you centrifuge them at a rate of about 40 revolutions per minute on a device that has a radius of about 3 metres that that provides sufficient loading if you do it only twice a day two one-hour doses to protect a lot of the systems of the body, but not all of them. Diana - So, centrifuging astronauts in a wheel similar to the ones you find at the fair ground may be one way of counteracting microgravity and its effects. On the forum, Clifford K said that, "Given gravity very slightly across the Earth, it should be expected that humans can tolerate some differences. But more research is needed to find out if an environment with less than 1G will still be sufficient to maintain good health over time." Next week, why not grow a moustache to answer this question.