Effects of microgravity on human physiology

Spaceflight exposes humans to a unique environment characterized by altered gravity, cosmic radiation and psychological stress, resulting in extensive physiological adaptations across multiple organ systems. This review provides a state-of-the-art overview of documented findings on the effects of microgravity on human physiology, combining data from both in-flight studies and ground-based simulations with a focus on underlying mechanisms. Evidence indicates that microgravity induces significant changes, including skeletal muscle atrophy, bone loss, immune dysregulation, cardiovascular remodelling, skin aging, and disruptions in respiratory, lymphatic, digestive, endocrine, urinary, and reproductive functions. Although countermeasures such as exercise, pharmacological interventions, and advanced monitoring techniques have shown promise in mitigating some of these effects, many adaptations persist post-flight, potentially compromising long-term astronaut health. This review highlights the need for continued research to develop targeted countermeasures that ensure astronaut safety during extended missions and to translate these findings into improved health outcomes on Earth.