title: Key influence of sex on urine volume and osmolality.
abstract: BACKGROUND
  Demographics influence kidney stone risk and the type of stone that is more likely to form. Common kidney stone risk factors include having a low urine volume and a high urine concentration. The goal of the current study was to evaluate the effect of demographics on urinary concentration and osmole excretion.
  
  
  METHODS
  Twenty-four-hour urine samples were collected from non-Hispanic white sibships in Rochester, MN. Height, weight, blood pressure, serum creatinine, and cystatin C were measured. Diet was assessed using the Viocare food frequency questionnaire. Effects of demographics and dietary elements on urine osmolality and volume were evaluated in bivariate and multivariable models, as well as models that included dietary interactions with age, sex, and weight.
  
  
  RESULTS
  Samples were available from 709 individuals (mean age 66 ± 9 years, 59 % female). Across the age spectrum, males had higher urine osmolality (~140 mOsm/kg, p < 0.0001) and total osmole excretion (~270 mOsm, p < 0.0001) compared to females. For any given urine volume, males had a consistently higher urine osmolality (~140 mOsm/kg, p < 0.0001). In multivariable models, urine osmolality declined with age and water intake and remained higher in males than females. Urine osmolality positively associated with weight and animal protein intake. Higher urine volume associated with larger water intake. An interaction revealed that greater body weight was associated with larger changes in urine osmolality as oxalate intake increased (p = 0.04).
  
  
  CONCLUSIONS
  Data from this study support the hypothesis that there are sex differences in thirst and vasopressin action. This trend in urine concentration is also consistent with known epidemiologic patterns of urinary stone disease risk.
authors: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 USA.
authors: Majuran
authors: M
authors: Perinpam
authors: Institute for Social Research, University of Michigan, Ann Arbor, MI USA ; Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI USA.
authors: Erin B
authors: EB
authors: Ware
authors: Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI USA.
authors: Jennifer A
authors: JA
authors: Smith
authors: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 USA.
authors: Stephen T
authors: ST
authors: Turner
authors: Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, MI USA.
authors: Sharon L R
authors: SL
authors: Kardia
authors: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 USA ; Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN USA.
authors: John C
authors: JC
authors: Lieske
keywords: Diet; Nephrolithiasis; Urine osmolality; Urine volume