Mineral Bone Density and Body Composition of Participants in Experiment Mars-500

The investigation of the bone system and body composition in the participants of the Mars-500 experiment (prior to and on completion of the experiment) employed dual-energy X-ray absorptiometry (DXA) using a HOLOGIC Delphy osteodensitometer according to the protocol used in examination of cosmonauts. The bone density of lumber vertebrae and femoral proximal epiphysis, as well as the body composition were measured. Statistically significant changes in the mineral density of lumber vertebrae were found in three subjects and displayed different trends from +2.6 to –2.4%. At the same time, in the femoral proximal epiphysis, including in the cervical region, the mineral density after the experiment was significantly lower in all participants. Four subjects exhibited an increase (by 5–9%) in the mineralization of the skull bones, as in some cosmonauts after flights. All participants were characterized by loss of adipose tissue mass (from 2 to 7 kg; in one subject, 20 kg, by a factor of three). Changes in lean mass (by 1–3 kg) were often negative and in the limbs might be associated with preferences for a certain type of physical activity. It is shown that prolonged stay in a confined space can lead to a decrease in mineralization of individual parts of the skeleton. Unlike real spaceflights and long-duration experiments with hypokinesia carried out earlier at the Institute for Biomedical Problems, no clinically significant loss of mineral density (osteoporosis, osteopenia) was observed in the Mars-500 experiment, which may be due to the lack of microgravity effects.