~Jon

The theory Jon described (body fluids influencing bone loss) was new to me. I was only aware of skeletal stresses being relevant. So I did a bit of net browsing. It seems modern models incorporate both.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090042802_2009043894.pdf

“Simulating Bone Loss in Microgravity Using Mathematical Formulations of Bone Remodeling” from 2009

“The model is formed by combining a previously developed set of biochemical, cellular dynamics, and mechanical stimulus equations”

Figures at the end show remarkable non-linear behavior for micro gravity. However, no attempt is made to apply the formula to lunar gravity.

http://weboflife.nasa.gov/currentResearch/currentResearchGeneralArchives/weakKnees.htm

“Researchers do not yet know whether the biomechanical stimuli that are changed by microgravity directly affect osteoblast and osteoclast function or if other physiological factors such as hormone levels or poor nutrition contribute to bone loss.”

http://www.lancet.com/journals/lancet/article/PIIS0140-6736%2880%2902208-8/fulltext

Effects vary indiviually: “one astronaut lost almost 8% after 84 days” which would be about 3% per month, while other astronauts experience only 1%. So some of us may be more fit for living on the moon than others?

http://adsabs.harvard.edu/full/1992lbsa.conf..569K

“Bone Loss and Human Adaption to Lunar Gravity” from 1992

With some assumptions (which may be true or not), they estimate bone mineral content (BMC) loss of 4 times slower for Moon gravity than for micro gravity.

Finally they say “it is not known whether these effects are self-limiting as they appear for immobilized patients on Earth.”

Hm, gloomy remarks like that are good to motivate research money.

In fact the monthly rate of bone loss is pretty irrelevant for living on the moon. The limit is relevant. The body adjusts bone mass and muscle mass to what is actually needed. And what will the equilibrium be on the Moon?

Yes, we don’t know for sure. Yes, experimental evidence is needed. But personally I believe if the effects are self-limiting on Earth at a near-healthy level (ok, ok, I know, I should do more exercise), then they are similarly self-limiting on the Moon. Which would mean living on the Moon would be ok, but before returning to Earth you should do some months of training and exercises to prepare for Earth gravity.

I could be wrong. And those people warning a hundred year ago that traveling at speeds higher than 30 km/h could lead to serious health problems could have been right.

Randy

Just another reason to get people living permanently in space and on “planetary” surfaces (by which I meant to include the Moon) ASAP. Nobody waited to colonize the New World ’til they could prove it was safe.