Space radiation effects and microgravity

Humans in space are exposed both to space radiation and microgravity. The question whether radiation effects are modified by microgravity is an important aspect in risk estimation. No interaction is expected at the molecular level since the influence of gravity is much smaller than that of thermal motion. Influences might be expected, however, at the cellular and organ level. For example, changes in immune competence could modify the development of radiogenic cancers. There are no data so far in this area. The problem of whether intracellular repair of radiation-induced DNA lesions is changed under microgravity conditions was recently addressed in a number of space experiments. The results are reviewed; they show that repair processes are not modified by microgravity