The Effect of Vitamin D Repletion on Kidney Stone Risk

The Effect of Vitamin D Repletion on Urinary Calcium Excretion in Kidney Stone Formers With Vitamin D Deficiency and High Urinary Calcium

Examine the effect of nutritional vitamin D repletion on urinary calcium excretion and kidney stone burden in calcium kidney stone formers

The investigators plan to conduct a clinic-based interventional study of 50 patients followed at Miriam Hospital Kidney Stone Clinic with history of nephrolithiasis, urinary calcium excretion between 150 and 400 mg/day, and 25-vitamin D deficiency/insufficiency (defined as serum level ≤ 30ng/ml). The intervention is oral ergocalciferol 50,000 IU per week for 12 weeks (repletion course). After that, the same repletion course will be repeated if serum 25-vitamin D remains ≤ 30ng/ml or drops to ≤ 30ng/ml anytime during the study. Otherwise, a maintenance dose of cholecalciferol 1,000 IU daily or ergocalciferol 50,000 IU monthly will be prescribed for the rest of the study. Each participant will serve as his own control. The outcome is the change in urinary calcium excretion and stone burden assessed by renal ultrasound. The planned study duration is 12 months. The investigators will have greater than 95% power to detect a 10% increase in 24-hour urinary calcium.

Inclusion Criteria:

• History of nephrolithiasis
• 25(OH)D deficiency (defined as serum level ≤ 30ng/ml) within 3 months of enrollment
• 24-hour urinary calcium excretion > 150 mg/day and < 400 mg/day (measured less than 2 months prior to study enrollment)

Exclusion Criteria:

• Known uric acid, cystine, or struvite stone disease
• Hypercalcemia (serum calcium >10.4 mg/dl within the past 12 months)
• Gross hematuria within the past 6 months
• Acute stone event within the past 1 month
• Recent stone intervention within the past 1 month
• Suspected or known secondary causes of hypercalciuria such as primary hyperparathyroidism, sarcoidosis, hyperthyroidism, or malignancy (except non-melanoma skin cancer)
• Addition or dose change of medicines potentially affecting urinary calcium since enrollment 24-hour urine collection (including diuretics, magnesium supplements, potassium supplements, potassium citrate, and vitamin D supplementation)
• Pregnancy