Additive Renoprotective Effects of Oral Calcitriol in IgA Nephropathy Patients Taking Renin-Angiotensin System Blockers

Inclusion Criteria: * Biopsy-proven Ig AN patients aged 20-70 years * Patients with residual proteinuria \> 500 mg/g creatinine despite renin-angiotensin system blockade and adequate blood pressure control for more than 3 months * Patients who give informed consent, and 4) estimated GFR \>= 30 ml/min/1.73 m2. Exclusion Criteria: * patients \< 20 years or \> 70 years * hypersensitivity to vitamin D analogs * patients who need urgent dialysis * hypercalcemia within 3 months (uncorrected serum calcium level \> 10.2 mg/dL) * clinical features of rapidly progressive glomerulonephritis * life expectancy less than 24 months * uncontrolled hypertension * decompensated liver or lung disease * symptomatic heart failure (NYHA class II-IV or LVEF \< 40%) * estimated GFR \< 30 ml/min/1.73 m2.