Space flight and the risk of renal stones.

Exposure to the microgravity environment results in many metabolic and physiological changes to humans. Body fluid volumes, electrolyte levels, and bone and muscle undergo changes as the human body adapts to the weightless environment. This investigation examined the role of these physiologic changes to the potentially serious consequences of renal stone formation. The influence of dietary factors on the urinary biochemistry were assessed. Data collected immediately after Space Shuttle flights indicated changes in the urine chemistry favoring an increased risk of calcium oxalate and uric acid stone formation (Whitson et al., 1993). During short term Shuttle space flights, in-flight changes observed included increased urinary calcium and decreased urine volume, pH and citrate resulting in a greater risk for calcium oxalate and calcium phosphate stone formation (Whitson et al, 1997). Results from long duration Shuttle-Mir missions followed a similar trend and demonstrated decreased fluid intake and urine volume resulting in a urinary environment saturated with the calcium stone-forming salts. The increased risk occurs rapidly upon exposure to microgravity, continues throughout the space flight and following landing.