Background: Urinary calcium is considered a risk factor for urinary stone disease (USD), although prospective data are missing. This epidemiologic study investigates cross-sectionally and longitudinally the relation of urinary calcium excretion to USD.
Methods: In the Gubbio Population Study, data on USD were collected by questionnaire during medical examinations from 1989 to 1992 (baseline) and telephone interviews in 1997 to 1998 (follow-up). Baseline data collection included overnight urinary calcium excretion and use of medications. Study cohort was made of 1458 men and 1799 women, age 25 to 74 years, and not on treatment with diuretics at baseline. USD was diagnosed by: excretion of stone(s), and/or radiographic or ultrasonic evidence, and/or surgical or endoscopic removal of stone(s).
Results: At baseline, urinary calcium excretion was higher in persons with than without USD (215 and 182 micromol/hour, P < 0.001) and related to USD prevalence independent of gender, age, and other variables (P < 0.001). Among persons without USD at baseline, baseline urinary calcium excretion was higher in persons with than without incident USD at follow-up (202 and 181 micromol/hour, P = 0.034) and related to incident USD independent of gender, age, and other variables. A difference of 100 micromol/hour (about 1 SD) in urinary calcium excretion related to a difference in USD risk of 1.32 for prevalence and 1.21 for incidence (95% CI = 1.15/1.52 and 1.01/1.45, respectively) in multivariate analyses controlled for gender, age, body mass index, parental history of USD, urinary excretion of urea, sodium, and potassium.
Conclusion: Cross-sectional and prospective data show that urinary calcium excretion is a risk factor for USD.