From the Guidelines
Vitamin D supplementation should be avoided in patients with calcium oxalate kidney stones, unless the patient has a deficiency, in which case careful supplementation with vitamin D3 (cholecalciferol) at 800-1000 IU daily is appropriate, with monitoring of both vitamin D and calcium levels. The role of Vitamin D in patients with calcium oxalate kidney stones is complex, and its supplementation can have both positive and negative effects on stone formation. While Vitamin D is essential for calcium absorption in the intestines, excessive Vitamin D can increase urinary calcium excretion, potentially worsening stone formation 1.
Key Considerations
- The relationship between Vitamin D and stone formation is not straightforward, as Vitamin D increases calcium absorption, but deficiency can paradoxically increase stone risk through secondary hyperparathyroidism.
- Patients with calcium oxalate stones should maintain adequate hydration (2-3 liters of fluid daily), moderate dietary calcium intake (1000-1200 mg daily), and limit sodium and animal protein consumption.
- Regular monitoring of urinary calcium excretion through 24-hour urine collections is recommended to assess the impact of Vitamin D supplementation on stone risk factors.
- A patient with calcium urolithiasis who wishes to continue calcium supplementation should collect 24-h urine samples on and off the supplement, and if the urinary supersaturation of the calcium salt in question increases during the period of supplement use, the supplement should be discontinued 1.
Dietary Recommendations
- Maintain adequate dietary calcium intake to reduce the risk of stone formation, as higher calcium intake can bind dietary oxalate in the gut, reducing oxalate absorption and urinary excretion 1.
- Limit sodium intake to less than 2.4 g/day, as high sodium intake can increase urinary calcium excretion.
- Reduce non-dairy animal protein intake to 5-7 servings of meat, fish, or poultry per week, as high animal protein intake can increase urinary calcium and uric acid excretion, and reduce urinary citrate excretion.
From the Research
Role of Vitamin D in Patients with Calcium Oxalate Kidney Stones
- The association between nutritional vitamin D supplements and the risk for stone formation is currently not completely understood 2.
- Circulating active vitamin D has been found to be increased in kidney stone formers, whereas higher plasma 25-hydroxycholecalciferol seems to be present only in hypercalciuric patients 2.
- Available evidence might suggest that vitamin D administration worsens the risk for stone formation in patients predisposed to hypercalciuria 2.
Dietary Recommendations for Patients with Calcium Oxalate Kidney Stones
- General dietary advice for kidney stone formers includes elevated fluid intake, dietary restriction of sodium and animal proteins, avoidance of a low calcium diet, maintenance of a normal body mass index, and elevated intake of vegetables and fibers 2.
- Balanced calcium consumption protects against the risk for kidney stones by reducing intestinal oxalate availability and its urinary excretion 2, 3.
- Restriction of dietary calcium enhances oxalate absorption and excretion, whereas an increase in calcium intake may reduce urinary oxalate excretion by binding more oxalate in the gut 3.
- Dietary oxalate restriction can reduce the risk of calcium oxalate stone formation, and patients are advised to decrease the consumption of foods that contain oxalate 4, 5.
Treatment and Prevention of Calcium Oxalate Kidney Stones
- Therapy to prevent stone recurrence is designed to reduce urinary supersaturation of Ca oxalate by increasing urine volume, reducing urine Ca to below 200 mg/24 hr with thiazide, maintaining dietary Ca intake at 600 to 800 mg/day, and adding potassium citrate if urine citrate levels are reduced 4.
- Increasing the intake of calcium may actually reduce the risk of calcium oxalate stone formation, and individuals with normal calcium intakes and lower intakes of protein and salt had a significantly reduced rate of calcium oxalate stone recurrence 6.