From the Guidelines
Calcium plays a crucial role in the formation of kidney stones, primarily through its involvement in calcium oxalate and calcium phosphate stones, which account for approximately 80% of all kidney stones. When urine becomes supersaturated with calcium and other stone-forming substances like oxalate or phosphate, these minerals can crystallize and form stones. This process begins when calcium binds with oxalate or phosphate in the urine, forming tiny crystals that gradually grow larger. Several factors increase this risk: high urinary calcium levels (hypercalciuria), which can result from excessive dietary calcium intake, increased intestinal calcium absorption, or abnormal kidney calcium handling; reduced urine volume due to dehydration, which concentrates stone-forming substances; and urinary pH changes that favor crystal formation. According to the American College of Physicians guideline 1, efforts to prevent the recurrence of nephrolithiasis target decreasing concentrations of the lithogenic factors (for example, calcium and oxalate) and increasing the concentrations of inhibitors of stone formation (for example, citrate). Key factors that influence calcium's role in kidney stone formation include:
- High urinary calcium levels (hypercalciuria)
- Reduced urine volume due to dehydration
- Urinary pH changes that favor crystal formation
- High sodium intake, which increases urinary calcium excretion
- High animal protein consumption
- Excessive vitamin D supplementation Despite calcium's role in stone formation, moderate dietary calcium (1,000-1,200 mg daily) is actually protective against stones when consumed with meals, as it binds to oxalate in the gut, preventing its absorption and subsequent urinary excretion. Paradoxically, low-calcium diets can increase stone risk by allowing more oxalate absorption. The American College of Physicians recommends management with increased fluid intake spread throughout the day to achieve at least 2 L of urine per day to prevent recurrent nephrolithiasis 1.
From the FDA Drug Label
The effect of oral Potassium Citrate therapy in a non-randomized, non-placebo controlled clinical study of five men and four women with calcium oxalate/calcium phosphate nephrolithiasis and documented incomplete distal renal tubular acidosis was examined Potassium Citrate therapy was associated with inhibition of new stone formation in patients with distal tubular acidosis. A moderate calcium restriction (400-800 mg/day) was imposed on patients with hypercalciuria All patients had a reduced stone formation rate. Over the first 2 years of treatment, the on-treatment stone formation rate was reduced from 13±27 to 1±2 per year.
The mechanism of action of calcium and kidney stone formation involves hypercalciuria, which can be reduced with a moderate calcium restriction of 400-800 mg/day. Potassium Citrate therapy is associated with inhibition of new stone formation in patients with distal tubular acidosis, and reduces the stone formation rate by increasing urinary citrate excretion and urinary pH 2.
- Key points:
- Hypercalciuria contributes to kidney stone formation
- Potassium Citrate therapy inhibits new stone formation
- Moderate calcium restriction reduces stone formation rate
- Urinary citrate excretion and urinary pH increase with Potassium Citrate therapy
From the Research
Calcium and Kidney Stone Mechanism of Action
- The relationship between calcium and kidney stone formation is complex, with increased urinary calcium potentially increasing the risk of kidney stones 3.
- However, some studies suggest that dietary calcium may actually reduce the risk of kidney stone formation, possibly due to its ability to bind to oxalate in the gut and reduce its absorption 3, 4.
- Hypercalciuria, or high levels of calcium in the urine, is a common cause of kidney stones, and treatments such as thiazide diuretics and potassium citrate may be effective in reducing urinary calcium excretion 5, 6.
Treatment Options
- Thiazide diuretics have been shown to be effective in reducing urinary calcium excretion and preventing kidney stone recurrence 5, 6.
- Potassium citrate may also be effective in reducing urinary calcium excretion and increasing citrate levels, which can help to prevent kidney stone formation 5, 6.
- Dietary modifications, such as increasing calcium intake and reducing oxalate and protein intake, may also be beneficial in preventing kidney stone recurrence 4, 7.
Dietary Recommendations
- A diet high in calcium (≥ 1 g/day) and low in protein and sodium may be protective against kidney stone formation 4.
- Increasing fluid intake to achieve a daily urine output of 2 liters may also be beneficial in preventing kidney stone recurrence 4.
- Avoiding foods high in oxalate, such as chocolate and cola, and increasing intake of fruits and vegetables, may also be helpful in preventing kidney stone formation 4, 7.