Crewmember demographic factors and their association with brain and ocular changes following spaceflight.

More people are traveling to space for longer durations than ever before. Many long-duration flyers exhibit signs of Spaceflight Associated Neuro-ocular Syndrome (SANS). A greater understanding of the mechanisms and predictors of SANS may lead to new, more individually tailored countermeasures. Our objective here was to determine whether brain and ocular changes with spaceflight are related to each other and/or to crewmember demographic factors, including sex, age, body mass index, and prior spaceflight experience. We assessed brain change and ocular change associations and predictive models of changes in a cohort study. Our samples included 30 crewmembers with brain MRI but not ocular metrics, 37 with ocular but not brain MRI, and 22 with both sets of data. Approximately 25% of participants in each of these samples were female. Females showed greater free water reduction around the vertex of the brain from pre- to postflight than males. While not statistically significant, the odds ratio of males developing signs of SANS was approximately three times higher than for females. Unlike in past smaller studies, we found no association between brain changes and the development of signs of SANS. Interpretation of these findings should be tempered by the fact that our sample included a relatively small number of females.