Abstract
INTRODUCTION: Low vitamin D is a possible risk factor among calcium oxalate (CaOx) stone formers, although its routine assessment and the role for supplementation remain controversial. This study aimed to examine the prevalence of low vitamin D in a large Canadian cohort and to assess the impact of replacement therapy on metabolic and radiographic outcomes. METHODS: A retrospective review of patients with CaOx stones who underwent a full metabolic evaluation, including two 24-hour urine collections in a multidisciplinary metabolic stone clinic, was conducted to determine the prevalence of 25-hydroxy vitamin D (25-OH vitamin D) deficiency/insufficiency. A subset of patients receiving vitamin D supplementation was assessed longitudinally for changes in metabolic parameters and stone growth and compared to a cohort with normal values. RESULTS: Among 748 patients, 64% had low vitamin D levels at baseline. These patients were more likely to be younger (53 [42.5-61] years vs. 57 [44-67], p<0.001), have a higher body mass index (BMI) (29.3 [25.7-33.3) kg/m(2) vs. 27.5 [24.3-31.9], p<0.001), and to be male (53.6 vs 44.4%, p=0.019). Among 83 patients receiving vitamin D with a mean followup of 4.8 years, none became hypercalcemic. Serial imaging demonstrated 41% had an increase in stone burden over time, which was not significantly different from those not requiring supplementation. CONCLUSIONS: Low vitamin D is very common among Canadian CaOx stone formers and should be a routine part of an in-depth metabolic workup. Vitamin D administration can be safely recommended to stone formers without risk of inducing stone progression.