title: Urine volume and its effects on renal stone risk in astronauts.
abstract: BACKGROUND
  Urine composition in astronauts during and immediately after spaceflight changes in ways that increase the renal stone-forming potential for calcium oxalate, calcium phosphate, and uric acid saturation. We examined the effect of urine volume on the risk of renal stone formation in 356 astronauts.
  
  
  METHODS
  Renal stone-forming risk was evaluated from 24-h urine samples collected from astronauts before and after 4- to 17-d Space Shuttle flights. Urinary chemistries were performed and the relative supersaturations of calcium oxalate, brushite, sodium urate, struvite, and uric acid saturation were calculated from the biochemical results.
  
  
  RESULTS
  Urinary supersaturation levels of stone-forming salts were inversely related to urinary output both before and after spaceflight. Urine volume > 2 L x d(-1) reduced the risk of renal-stone development without affecting urinary citrate concentrations as compared with the increased risk observed in those astronauts who excreted urine volumes < L x d(-1).
  
  
  CONCLUSIONS
  Results from this study indicate that increasing daily urinary output alone is an effective countermeasure to reduce the renal stone-forming risk immediately after spaceflight. However, increasing urinary output during flight may not be entirely effective in minimizing the potential risk of renal stone formation due to the changes in the urine chemistry in astronauts exposed to microgravity.
  
  
  BACKGROUND
  urine volume, spaceflight, renal calculi.
authors.affiliation: NASA-Johnson Space Center, Astronaut Office, Houston, TX 77058, USA. peggy.a.whitson1@jsc.nasa.gov
authors.forename: P A
authors.initials: PA
authors.lastname: Whitson
authors.forename: R A
authors.initials: RA
authors.lastname: Pietrzyk
authors.forename: C F
authors.initials: CF
authors.lastname: Sams
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D018480:Astronauts; D002118:Calcium / Q000652:urine*; D002129:Calcium Oxalate / Q000032:analysis; D005118:Extraterrestrial Environment; D006801:Humans; D007669:Kidney Calculi / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D012307:Risk Factors; D013026:Space Flight; D014556:Urine
chemical_list: D002129:Calcium Oxalate; D002118:Calcium