Causes of Kidney Stones
Kidney stones are primarily caused by a combination of dietary factors, metabolic abnormalities, and inadequate fluid intake that lead to supersaturation of stone-forming salts in the urine. 1, 2
Major Risk Factors
Dietary Factors
Low fluid intake: Inadequate hydration is a primary risk factor as it leads to concentrated urine and increased supersaturation of stone-forming minerals 1
Calcium intake: Both excessively low and high calcium intake can increase stone risk 1
- Low dietary calcium paradoxically increases risk by allowing more oxalate absorption in the gut
- Recommended intake is 1,000-1,200 mg/day from dietary sources
High sodium consumption: Increases urinary calcium excretion and stone risk 1, 2
- Sodium restriction to <2,300 mg/day is recommended
Animal protein excess: Increases urinary calcium and uric acid excretion while reducing urinary citrate 1
- Moderate consumption (5-7 servings/week) is recommended
High oxalate foods: Increase urinary oxalate excretion 1, 2
- Major sources include spinach, rhubarb, beets, nuts, chocolate, tea, wheat bran, and strawberries
High sugar intake: Increases urinary calcium excretion 1
Vitamin C supplements: Can increase oxalate generation and excretion 1
Metabolic Abnormalities
Hypercalciuria: Excessive urinary calcium excretion 1, 2
- Can be idiopathic or secondary to conditions like hyperparathyroidism
Hyperoxaluria: Elevated urinary oxalate levels 2
- Can be primary (genetic) or secondary to dietary factors or intestinal disorders
Hypocitraturia: Low urinary citrate levels 1, 2
- Citrate is a natural inhibitor of stone formation
Hyperuricosuria: Excessive urinary uric acid 1, 2
- Often related to high purine diet or metabolic disorders
Renal tubular acidosis: Leads to persistently alkaline urine and hypocitraturia 2, 3
Cystinuria: Genetic disorder causing excessive urinary cystine 2
Medical Conditions
Obesity: Significantly increases risk of stone formation 1, 2
- The impact is greater in women than men
Diabetes and metabolic syndrome: Increase risk of stone formation 4
Inflammatory bowel disease: Causes malabsorption that can lead to stone formation 2
Recurrent urinary tract infections: Associated with struvite stones 1, 2
Stone Types and Specific Causes
Calcium Stones (80% of all stones)
Calcium oxalate stones:
Calcium phosphate stones:
Uric Acid Stones (5-10%)
- Primarily caused by persistently acidic urine (pH <5.5) 2, 3
- Risk factors include high purine diet, gout, and metabolic syndrome
- Dehydration and low urine volume exacerbate risk
Struvite Stones (5-15%)
- Caused by urinary tract infections with urease-producing bacteria 1, 2
- These bacteria (like Proteus) split urea into ammonia, creating alkaline urine
- More common in women and those with frequent UTIs
Cystine Stones (1-2%)
- Caused by cystinuria, a genetic disorder of amino acid transport 2
- Results in excessive urinary cystine that precipitates at normal urine pH
Medications That Increase Stone Risk
- Certain antibiotics: Can increase risk of stone formation 2, 5
- Protease inhibitors: Associated with increased stone risk 5
- Some diuretics: Can alter urinary composition and increase stone risk 2, 5
Prevention Strategies
- Increase fluid intake: Maintain urine output >2L/day 1, 2
- Moderate dietary calcium: 1,000-1,200 mg/day from food sources 1, 2
- Reduce sodium intake: <2,300 mg/day 1
- Limit animal protein: 5-7 servings/week 1
- Increase fruits and vegetables: Raises urinary citrate and urine pH 1, 2
- Avoid high oxalate foods if hyperoxaluria is present 1, 2
By addressing these risk factors through dietary modifications and treating underlying metabolic abnormalities, the risk of kidney stone formation can be significantly reduced.