title: Acute caffeine effects on urine composition and calcium kidney stone risk in calcium stone formers.
abstract: OBJECTIVE
  Caffeine increases urinary calcium (ca) excretion in nonstone formers. We designed a study to determine the effect of caffeine consumption on urinary composition in stone formers.
  
  
  METHODS
  A total of 39 normocalcemic patients with calcium stones consumed caffeine (6 mg/kg lean body mass) after 14 hours of fasting. Urinary composition was compared 2 hours before and 2 hours after caffeine consumption. Control subjects included 9 nonstone formers studied contemporaneously with patients plus data from 39 nonstone formers from previous studies matched to each patient by level of fasting calcium/creatinine (Cr), gender and age.
  
  
  RESULTS
  Caffeine increased urinary Ca/Cr, magnesium/Cr, citrate/Cr and sodium/Cr but not oxalate/Cr in stone formers and controls. The Tiselius stone risk index for calcium oxalate precipitation increased from 2.4 to 3.1 in stone formers and from 1.7 to 2.5 in nonstone formers. Of the 39 stone formers 32 had an increased Tiselius risk index after caffeine. Post-caffeine increases in Ca/Cr and Na/Cr were highly correlated.
  
  
  CONCLUSIONS
  Caffeine consumption may modestly increase risk of calcium oxalate stone formation.
authors.affiliation: Department of Food Science and Human Nutrition, Washington State University, Spokane, 99120-1495, USA. massey@wsu.edu
authors.forename: Linda K
authors.initials: LK
authors.lastname: Massey
authors.forename: Roger A L
authors.initials: RA
authors.lastname: Sutton
mesh_terms: D000208:Acute Disease; D000328:Adult; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000652:urine; D002129:Calcium Oxalate / Q000032:analysis; D011232:Chemical Precipitation; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000737:chemistry* / Q000652:urine*; D008297:Male; D008875:Middle Aged; D013054:Spectrophotometry, Atomic; D014556:Urine / Q000737:chemistry*
chemical_list: D002129:Calcium Oxalate; D002110:Caffeine; D003404:Creatinine; D002118:Calcium