Astronauts lose 2% of bone mass for each month they are exposed to the effects of microgravity. So far, astronauts have not been exposed to the increased radiation of outer space, but that will change when they undertake a proposed 30-month trip to Mars, Bateman said. NASA has focused on radiation's cancer-causing properties and its ability to compromise the central nervous and immune systems. But the effect on bone health is an unexamined concern.
The murine (mouse) model such as the one in this study provides a way to study the physiological effects of radiation using controlled experiments. Clinical studies of people who undergo radiation to treat cancer are limited because of the complicating factors of the illness itself and the chemotherapy which often accompanies it. "You can't study this in people, so having a well-defined animal model is important," Bateman said.
Study focuses on four types of radiation
In the current study, the mice received a single 2 Gray (Gy) dose, which is comparable to the single dose of 1-2 Gy that human cancer patients receive. However, cancer patients receive a series of doses over the course of therapy, totaling 10-70 Gy. (The amount of radiation in a Gy varies, because it is calculated based on the recipient's weight.)
The mice were divided into five groups. The control group received no radiation. Each of the remaining four groups received a different type of radiation: gamma, proton, ion or carbon. Those exposed to the carbon radiation suffered 39% spongy bone loss; proton, 35%; ion, 34%; and gamma, 29%. The loss of spongy connections in the four groups ranged from 46-64%, he said.
Cancer patients typically receive either gamma or, less commonly, proton radiation. Astronauts on a Mars mission are expected to receive extended periods of low-dose radiation of multiple types, including protons and heavy ions, Bate
Source:American Physiological Society