title: Demographic, dietary, and urinary factors and 24-h urinary calcium excretion.
abstract: OBJECTIVE
  Higher urinary calcium is a risk factor for nephrolithiasis. This study delineated associations between demographic, dietary, and urinary factors and 24-h urinary calcium.
  
  
  METHODS
  Cross-sectional studies were conducted of 2201 stone formers (SF) and 1167 nonstone formers (NSF) in the Health Professionals Follow-up Study (men) and Nurses' Health Studies I and II (older and younger women).
  
  
  RESULTS
  Median urinary calcium was 182 mg/d in men, 182 mg/d in older women, and 192 mg/d in younger women. Compared with NSF, urinary calcium as a fraction of calcium intake was 33 to 38% higher in SF (P values < or =0.01). In regression analyses, participants were combined because associations with urinary calcium were similar in each cohort and in SF and NSF. After multivariate adjustment, participants in the highest quartile of calcium intake excreted 18 mg/d more urinary calcium than those in the lowest (P trend =0.01). Caffeine and family history of nephrolithiasis were positively associated, whereas urinary potassium, thiazides, gout, and age were inversely associated, with urinary calcium. After multivariate adjustment, participants in the highest quartiles of urinary magnesium, sodium, sulfate, citrate, phosphorus, and volume excreted 71 mg/d, 37 mg/d, 44 mg/d, 61 mg/d, 37 mg/d, and 24 mg/d more urinary calcium, respectively, than participants in the lowest (P values trend < or =0.01).
  
  
  CONCLUSIONS
  Intestinal calcium absorption and/or negative calcium balance is greater in SF than NSF. Higher calcium intakes at levels typically observed in free-living individuals are associated with only small increases in urinary calcium.
authors.affiliation: Renal Division and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. entaylor@partners.org
authors.forename: Eric N
authors.initials: EN
authors.lastname: Taylor
authors.forename: Gary C
authors.initials: GC
authors.lastname: Curhan
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D002136:Calcium, Dietary / Q000652:urine*; D019343:Citric Acid / Q000652:urine; D003710:Demography; D005260:Female; D005500:Follow-Up Studies; D006073:Gout / Q000453:epidemiology; D006801:Humans; D053565:Hypercalciuria / Q000453:epidemiology* / Q000208:ethnology / Q000652:urine*; D008274:Magnesium / Q000652:urine; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D053040:Nephrolithiasis / Q000453:epidemiology* / Q000208:ethnology / Q000652:urine*; D010758:Phosphorus / Q000652:urine; D012307:Risk Factors; D012964:Sodium / Q000652:urine; D013431:Sulfates / Q000652:urine; D014556:Urine
chemical_list: D002136:Calcium, Dietary; D013431:Sulfates; D010758:Phosphorus; D019343:Citric Acid; D012964:Sodium; D008274:Magnesium