Relationship Between Serum Vitamin D and 24-hour Urine Calcium in Patients with Nephrolithiasis

Objective: To examine the relationship between serum 25-OH vitamin D and 24-hour urine calcium in patients with nephrolithiasis.

Methods: A retrospective review was performed. Patients evaluated in 2 metabolic stone clinics were included for analysis. Multivariate linear regression models were adjusted for known risk factors for stone disease (age, gender, body mass index, hypertension, diabetes mellitus, gout, relevant medications, and 24-hour urine composition).

Results: One-hundred sixty-nine patients were included in the study. Female to male ratio was 69:100, mean age was 50.9 years (SD 13.7), and mean body mass index was 27.4 (SD 6.4). Vitamin D deficiency (25-OH vitamin D <20 ng/mL) was present in 18.9% of patients, vitamin D insufficiency (>20, <30 ng/mL) was present in 34.9% of patients, and vitamin D was within normal limits (≥ 30 ng/mL) in 46.1% of patients. On age-adjusted and multivariate linear regression, serum 25-OH vitamin D was not related to 24-hour urine calcium (age adjusted β = -0.31 m 95% CI -1.9 to 1.3; multivariate adjusted β = 0.08, 95% CI -1.3 to 1.5).

Conclusion: Although 25-OH vitamin D is involved in the body's calcium homeostasis, our study does not show a relationship between serum vitamin D level and 24-hour urine calcium excretion in stone-formers. This information may have implications regarding the safety of vitamin D repletion in patients with nephrolithiasis.