From the Guidelines
To prevent calcium kidney stones, increasing fluid intake to achieve at least 2 L of urine per day is recommended. This is based on the guideline from the American College of Physicians, which suggests that increased fluid intake is associated with a reduction in stone recurrence 1.
Key Recommendations:
- Drink plenty of water: Aim for at least 2-3 liters daily to keep urine diluted and reduce mineral concentration.
- Limit sodium intake: Less than 2,300 mg per day, as high sodium increases calcium excretion in urine.
- Moderate animal protein consumption: 6 ounces daily, since excess protein can increase stone risk.
- Include calcium-rich foods: 1,000-1,200 mg daily with meals, rather than supplements, as dietary calcium binds to oxalate in the gut, preventing its absorption.
- Reduce oxalate-rich foods: Like spinach, rhubarb, nuts, and chocolate if prone to calcium oxalate stones.
- For those with recurrent stones, medications like thiazide diuretics (hydrochlorothiazide 25-50 mg daily), potassium citrate (10-15 mEq twice daily), or allopurinol (100-300 mg daily) may be prescribed based on specific stone composition and urine chemistry 1.
- Regular exercise and maintaining a healthy weight also help reduce stone risk by decreasing urinary supersaturation of stone-forming minerals and increasing substances that inhibit crystal formation in the kidneys.
Rationale:
The American College of Physicians guideline recommends management with increased fluid intake and pharmacologic monotherapy with a thiazide diuretic, citrate, or allopurinol to prevent recurrent nephrolithiasis in patients with active disease in which increased fluid intake fails to reduce the formation of stones 1. The evidence from these studies supports the use of these measures to prevent calcium kidney stones, with a focus on reducing morbidity, mortality, and improving quality of life.
Considerations:
- The choice of treatment could be based on the type of metabolic abnormality, but evidence from randomized, controlled trials is lacking to correlate the drug of choice and stone type to the prevention of stone recurrence 1.
- The available evidence evaluated higher doses of thiazides to prevent recurrent nephrolithiasis, but the effectiveness of lower doses is not known 1.
- All medications are associated with adverse events, which should be considered when prescribing 1.
From the FDA Drug Label
The dose of allopurinol tablets recommended for management of recurrent calcium oxalate stones in hyperuricosuric patients is 200 to 300 mg/day in divided doses or as the single equivalent Clinical experience suggests that patients with recurrent calcium oxalate stones may also benefit from dietary changes such as the reduction of animal protein, sodium, refined sugars, oxalate-rich foods, and excessive calcium intake, as well as an increase in oral fluids and dietary fiber A fluid intake sufficient to yield a daily urinary output of at least 2 liters and the maintenance of a neutral or, preferably, slightly alkaline urine are desirable
To prevent calcium kidney stones, the following measures can be taken:
- Medication: Allopurinol tablets can be used at a dose of 200 to 300 mg/day in divided doses or as a single equivalent, as recommended for the management of recurrent calcium oxalate stones in hyperuricosuric patients 2
- Dietary changes: Reduction of:
- Animal protein
- Sodium
- Refined sugars
- Oxalate-rich foods
- Excessive calcium intake
- Increase:
- Oral fluids
- Dietary fiber
- Maintain a daily urinary output of at least 2 liters and a neutral or slightly alkaline urine 2
From the Research
Prevention of Calcium Kidney Stones
To prevent calcium kidney stones, several dietary recommendations and lifestyle changes can be implemented:
- Increase fluid intake to produce at least 2 liters of urine per day 3, 4
- Maintain a sufficient calcium consumption of 1200 mg per day, as low-calcium diets can promote stone formation 3
- Limit daily protein intake to 1 g/kg body weight, as a diet rich in meat protein carries an increased risk for forming upper urinary tract stones 3
- Consume high quantities of fruits and vegetables, as they raise urinary excretion of citrate, an important inhibitor of crystallization 3
- Prefer soft water over hard water for extra meal intake, as it is associated with a lower risk for recurrence of calcium stones 5
Dietary Recommendations
Dietary factors play an important role in the formation of calcium oxalate stones:
- Achieve adequate fluid intake to produce at least 2 liters of urine per day 4
- Avoid calcium restriction, except in rare instances of excessive intake 4
- Maintain dietary calcium intake at 600 to 800 mg/day 6
- Add potassium citrate if urine citrate levels are reduced 6
- Reduce urine oxalate excretion by dietary oxalate restriction if elevated 6
Urinary Risk Factors
Urinary risk factors for kidney stones include: