What causes calcium kidney stones?

Causes of Calcium Kidney Stones

Calcium kidney stones are primarily caused by high urinary calcium excretion, high sodium intake, low fluid intake, and dietary factors that affect urinary supersaturation of calcium salts. 1

Major Risk Factors for Calcium Stone Formation

Dietary Factors

• High sodium intake - Increases urinary calcium excretion by reducing renal tubular calcium reabsorption 1, 2
• Low fluid intake - Leads to concentrated urine and increased supersaturation of calcium salts 1
• High animal protein consumption - Creates an acid load that increases urinary calcium excretion and reduces urinary citrate excretion 1
• High sucrose (sugar) intake - Increases urinary calcium excretion, possibly mediated by insulin 1
• High vitamin C supplementation - Can be metabolized to oxalate; supplements of 1000mg or more daily increase stone risk by 40% 1
• Calcium supplements taken between meals - May increase stone risk by not binding dietary oxalate in the gut 1

Metabolic Factors

• Hypercalciuria - Excessive urinary calcium excretion is the most common metabolic abnormality in calcium stone formers 3
• Hyperoxaluria - Elevated urinary oxalate increases risk of calcium oxalate stone formation 1
• Hypocitraturia - Low urinary citrate reduces inhibition of calcium crystal formation 4
• Elevated urinary pH - Significantly increases risk of calcium phosphate crystal formation 4

Specific Dietary Components and Their Effects

Calcium

• Contrary to previous beliefs, low dietary calcium intake increases stone risk by allowing more oxalate absorption in the gut 5, 6
• Adequate dietary calcium (1,000-1,200 mg/day) is recommended for stone prevention 7
• Calcium supplements may increase stone risk if taken between meals rather than with food 1, 8
• Recent research suggests that a balanced calcium to phosphorus ratio (0.55-0.68) may be optimal for reducing stone risk 9

Oxalate

• High oxalate foods can increase risk in susceptible individuals 1
• Calcium stone formers with hyperoxaluria should limit intake of high-oxalate foods including:
  • Certain nuts (almonds, peanuts, cashews, walnuts, pecans) 1
  • Certain vegetables (beets, spinach) 1
  • Wheat bran, rice bran, and chocolate 1

Sodium

• High sodium intake directly increases urinary calcium excretion 1, 2
• Sodium restriction to <2,300 mg/day is recommended for all calcium stone formers 7, 2
• Randomized trials confirm the powerful effect of sodium restriction on reducing urinary calcium excretion 2

Potassium

• Low potassium intake can increase urinary calcium excretion 1
• Potassium-rich foods (fruits and vegetables) provide an alkali load that increases urinary citrate, an important inhibitor of stone formation 1
• Higher potassium intake is inversely associated with stone formation in men and older women 1

Medications That Can Cause Calcium Stones

• Acetazolamide - Increases urinary pH, which promotes calcium phosphate crystal formation 4
• Other medications that can increase stone risk include:
  • Loop diuretics (increase urinary calcium)
  • Vitamin D supplements (may increase intestinal calcium absorption) 8

Prevention Strategies

• Maintain high fluid intake to achieve urine volume >2.5 liters/day 1, 7
• Limit sodium intake to <2,300 mg/day 7, 2
• Consume adequate dietary calcium (1,000-1,200 mg/day) 7
• Limit animal protein intake 1, 7
• Increase fruit and vegetable consumption to increase urinary citrate 1, 7
• Avoid excessive vitamin C supplementation 1
• Take calcium supplements with meals rather than between meals if needed 1, 8

Common Pitfalls in Management

• Restricting dietary calcium - This actually increases stone risk by allowing more oxalate absorption 7, 6
• Focusing only on calcium restriction - A comprehensive approach addressing multiple dietary factors is more effective 7
• Not following up with 24-hour urine collections - These are essential to evaluate the impact of dietary changes 7
• Ignoring sodium intake - Sodium restriction is crucial for reducing urinary calcium excretion 2