Can we spend more time in space? Think about living on the moon or Mars? Four decades of research say that our bones could be standing in the way–more specifically, the bone loss humans experience in space.
As early as the Gemini flights, in 1963, we recognized that astronauts experienced significant bone loss during spaceflight. Astronauts and cosmonauts on the MIR Space Station lost as much bone in 1 month as post-menopausal women lose in 1 year.
The earth’s gravity creates a cycle of bone breakdown and build up that keeps our bones strong and healthy. Exercise—particularly walking—weight lifting, and resistance training are important to the maintenance of our skeletons. The more we bang our bones around, the more calcium they absorb and the stronger they become. But in space, there is no gravity to help build up our bones.
During spaceflight, astronauts also may not get enough vitamin D, which our bodies need to use calcium. Supplements don’t solve the problem–our bodies get rid of calcium in space, even if we give our bodies extra calcium and vitamin D. In fact, astronauts have so much extra calcium in their blood and urine they are at higher risk of developing kidney stones. One unfortunate Russian cosmonaut actually passed a kidney stone during a mission—which has to rank high on his list of unpleasant life experiences.
Scientists have created special exercise machines for use during spaceflight that attempt to create the force of gravity. But, experts like Peter Cavanagh, PhD, DSc, from the Center for Space Medicine in Cleveland, Ohio, have speculated that our astronauts may not be doing enough exercise during space flights to slow down bone loss. It takes a lot of time to set up and stow away exercise equipment, cutting down on exercise opportunities.
But astronauts don’t experience bone loss evenly throughout their bodies–it seems to be more dramatic in the spine and legs than their upper bodies. That’s because during spaceflight, the legs are used mainly for balance and positioning, whereas the arms are used to pull the astronauts around the spacecraft and to operate tools and instruments. That accidental exercise may be preventing bone loss in the upper skeleton. So, if load-bearing exercises can be developed for the lower body, bone loss could be halted or at least slowed down.
When astronauts eventually land on Mars and start drilling for soil samples or driving land rovers, will the loss of bone put them at higher risk for broken bones? Will their bones be able to heal in zero gravity or reduced gravity? We don’t know yet–but we don’t remember Dr. Spock or Captain Kirk ever worrying about their bones.