Dynamics of the body liquids and composition in long-duration space flight (Bioimpedance Analysis)

Bioimpedance measurement was used to study dynamics of human hydration status and body composition on board the International space station (ISS). At different stages of 100- to 200-day flights of 12 cosmonauts, the volume of their body liquid was reduced: the overall, intra-, and extracellular volumes became on average 5.2 to 10.4% less per group as compared to the baseline level. The in-flight changes in the body composition of the cosmonauts were also consistent: while the lean mass loss determined by impedance measurement was insignificant (on average, from 1.9 to 4.0%), the gain of the fatty mass ranged from 4.6 to 8.2% during the first three months of the flight. Thus, hydration of a human body decreased during the long-term space flight, which was accompanied by reduction of the muscular mass and the gain in fatty mass.