Hazards of human spaceflight

In Einstein's famous twin paradox, the effect of special relativity causes aging to slow in one twin during travel in a high-speed rocket through space while the body of the Earth-bound twin undergoes the same wear and tear that all humans experience on Earth (1). However, real space travels present far more realistic challenges that can potentially compromise the health of the more adventurous twin. On page 144 of this issue, Garrett-Bakelman et al. (2) investigate the manifold biological consequences of a journey in space endured by an astronaut during a 1-year mission onboard the International Space Station (ISS) compared with his identical twin on Earth. The challenges encountered in space include noise, isolation, hypoxia, and disrupted circadian rhythm (body clock). Furthermore, exposure to ionizing radiation (IR) and weightlessness, also called microgravity, could cause important health risks.