Inclusion Criteria:

- History of nephrolithiasis as per medical record

- Urinary calcium excretion between 150 and 400 mg/day (measured within 3 months of
study enrollment)

- 25(OH)D deficiency or insufficiency (defined as a serum level < 30 ng/ml) within 3
months of enrollment

Exclusion Criteria:

- Pregnant women, since the optimal dose of vitamin D supplementation in this
population has not been rigorously studied.

- Known uric acid, cystine, or struvite stone disease (because our intervention is
predominantly aimed at patients with calcium stone disease). An exception to this is
patients who have passed both uric acid and calcium stones, or patients who have
passed stones of mixed composition (uric acid and calcium).

- Hypercalcemia (serum calcium > 10.4 mg/dL) at baseline

- Acute stone event or gross hematuria (blood in the urine) within the past 2 months

- Recent stone intervention within the past 1 month

- Suspected or known secondary causes of hypercalciuria, such as primary
hyperparathyroidism, sarcoidosis, hyperthyroidism, or malignancy (except nonmelanoma
skin cancer)

- Addition or dose change of medicines potentially affecting urinary calcium since the
baseline 24hour urine collection (including diuretics, magnesium supplements,
potassium supplements, potassium citrate, and vitamin D supplementation)