Calcium and Phosphorus Whole-Body Balance and Kinetics in Patients With Moderate Chronic Kidney Disease

Inclusion Criteria: * Men or women, ages 30-75 years old, any race or ethnicity * Moderate chronic kidney disease * Female subjects must be postmenopausal (\>12 months since last menstrual period), surgically sterile, or confirmed not pregnant by pregnancy test * Must be on stable doses of medications (except those noted in exclusion criteria) for at least 4 weeks prior to the study * Willing to discontinue nutritional supplements (e.g. vitamin D, calcium, multivitamin/minerals, or others) upon enrollment until completion of the study * Adequate vitamin D status defined as serum 25D \> 20 ng/mL Exclusion Criteria: * Plans to initiate dialysis within 6 months * Hypercalcemia defined as serum calcium \>10.5 mg/dL within past 3 months * Hyperkalemia defined as serum potassium \>5.5 mg/dL within past 3 months * Hyperphosphatemia defined as serum phosphate \>5.5 mg/dL within past 3 months * Intestinal disease that alters absorption or normal intestinal function including celiac disease, small bowel resection, or bariatric surgery * Serious, uncontrolled underlying systemic disease including diabetes, lupus, hypertension * Pregnant or breastfeeding * Prescribed a phosphate binder medication, calcitriol, vitamin D analogs, calcimimetics, parathyroid hormone analogues, and other medications that may alter Ca and P metabolism within past 30 days