Idiopathic Calcium Nephrolithiasis and Hypovitaminosis D: a Case-Control Study

OBJECTIVE: To investigate the association between vitamin D deficiency (25-hydroxyvitamin D <20 ng/ml) and idiopathic calcium nephrolithiasis (ICN). METHODS: 884 ICN patients (363 males, mean age 51±14) and 967 controls (162 males, mean age 59±15) from an area with no food fortification policy were considered following a case-control study design. Patients were enrolled at a third-level outpatient stone clinic. Controls were selected from a laboratory database after exclusion of those with nephrolithiasis, bone, endocrine, liver and kidney diseases. Serum 25-hydroxyvitamin-D (25-OH-D), date of test, presence/history of diabetes and cardiovascular disease including hypertension were recorded for all subjects. Serum parathormone, calcium, phosphorus and urinary factors of lithogenic risk were available in stone formers (SF). After univariate statistical analysis, propensity score matching with conditional logistic regression was used to control for the possible effects of covariates. RESULTS: The prevalence of 25-OH-D <20 ng/ml was 56% in SF and 44% in controls (p<0.001), with median levels of 18 ng/ml (IQR 12-24) vs 23 ng/ml (IQR 14-30) (age- and sex-adjusted p<0.001). After a fully-adjusted conditional logistic regression analysis, performed on propensity-matched cohorts (442 SF, 442 controls), there was a statistically significant association between vitamin D deficiency and odds of nephrolithiasis (estimated OR 2.29, IC 95% 1.74-3.02, p<0.001). 25-OH-D levels were not different in hypercalciuric and normocalciuric SF (median and IQR 18 ng/ml, 13-23, vs 19 ng/ml, 13-26, p=0.2). CONCLUSIONS: Stone formers have lower serum 25-OH-D levels than controls. The role of hypovitaminosis D in the onset of ICN should be better reconsidered.