Bone loss in microgravity

Abstract

That bone is lost in space is now commonly known, but this recognition was quite a surprise when human spaceflight began. What is less well known, but no less true, is that the loss concentrates on the leg bones. Is it caused by fluid shifts, simple mechanics or space food? Loss of density in the leg bones can amount to a reduction of one-quarter within 6 months of spaceflight (Vico et al. 2000), a magnitude and rate that seem to outweigh the bone losses of 5–10% experienced by women after menopause. A substantial risk of fracture would thus arise for longterm missions were they done without adequate countermeasures. So, how could we try to prevent that kind of bone loss, or, as the physiologist would say, what is the cause of it?