In Reply I thank Zuidema and colleagues for their interest in our study on changes of blood-based biomarkers in long-duration space flyers after return to Earth from a 6-month mission aboard the International Space Station (ISS).1 I agree that the methods used in our longitudinal study could open the door to accessible and precise health surveillance of astronauts’ neurological health in future space missions. I concur with the need to replicate the findings from our pilot study in another sample. Small sample sizes are an intrinsic challenge for all spaceflight-associated research, and such studies are only powered to detect large effect sizes as observed in our study. Repeated within-participant measures can help overcome some of the constraints related to small samples. Our study was hypothesis driven because several neuroimaging studies from our group had identified detrimental effects on brain structure in long-duration cosmonauts,2-4 increasing the plausibility of our findings.