What are the causes of kidney stones?

Causes of Kidney Stones

Kidney stones are primarily caused by low fluid intake, dietary factors (high sodium, animal protein, and oxalate intake), metabolic abnormalities, and certain medical conditions. 1

Major Risk Factors

Fluid and Diet-Related Factors

• Low fluid intake: The most fundamental risk factor, leading to concentrated urine and increased supersaturation of stone-forming minerals 1
• Dietary calcium intake: Both excessively low and high calcium intake increase stone risk; recommended intake is 1,000-1,200 mg/day from dietary sources 1
• High sodium consumption: Increases urinary calcium excretion; restriction to <2,300 mg/day is recommended 1
• Excessive animal protein: Increases urinary calcium and uric acid excretion while reducing urinary citrate 1
• High oxalate foods: Major sources include spinach, rhubarb, beets, nuts, chocolate, tea, wheat bran, and strawberries 1
• High sugar intake: Increases urinary calcium excretion 1
• Vitamin C supplements: Can increase oxalate generation and excretion 1

Metabolic Abnormalities

1. Hypercalciuria: Excessive urinary calcium excretion, can be idiopathic or secondary to conditions like hyperparathyroidism 1
2. Hypocitraturia: Low urinary citrate levels, which normally inhibit stone formation 1
3. Hyperuricosuria: Excessive urinary uric acid, often related to high purine diet or metabolic disorders 1

Medical Conditions

• Obesity: Significantly increases stone risk, with greater impact in women than men 2, 1
• Hypertension: Associated with increased stone risk 2, 1
• Recurrent urinary tract infections: Associated with struvite stone formation 2, 1
• Diabetes: Associated with increased risk of stone disease 2

Stone Types and Their Specific Causes

Calcium Oxalate Stones (Most Common)

• Caused by high urinary calcium, high oxalate, low citrate, and low urine volume 1
• Dietary factors include high sodium, high animal protein, high oxalate, and low calcium intake 1

Struvite Stones

• Caused by urinary tract infections with urease-producing bacteria 1
• These bacteria split urea into ammonia, creating alkaline urine 1

Uric Acid Stones

• Associated with high purine diet, gout, and conditions causing high uric acid levels 3
• Low urine pH is a critical factor 3

Cystine Stones

• Caused by genetic disorders affecting cystine transport in the kidneys 4

Genetic Factors

• Monogenic causes have been identified in up to 30% of children and 10% of adults who form stones 4
• Approximately 35 different genes have been implicated in stone formation 4
• Genome-wide association studies have identified genes involved in renal tubular handling of lithogenic substances 4

Medication-Related Causes

• Protease inhibitors: Increase risk of certain stone types 3
• Some antibiotics: Can alter urinary composition and increase stone risk 3
• Certain diuretics: May increase stone risk through effects on urinary calcium excretion 3

Environmental and Demographic Factors

• Age: Peak incidence between 31-45 years 5
• Gender: Historically more common in men, though the gender gap is closing 2
• Geographic location: Higher prevalence in certain regions (e.g., "stone belt" regions) 5
• Socioeconomic status: Lower socioeconomic status associated with higher risk in some studies 5
• Climate and seasonality: Dehydration in hot climates or seasons increases risk 6

Common Pitfalls in Understanding Kidney Stone Causes

• Misconception about calcium intake: Many patients incorrectly reduce calcium intake, which can actually increase stone risk by allowing more oxalate absorption 7
• Focus on single factors: Stone formation is typically multifactorial, requiring comprehensive assessment 1
• Overlooking medications: Failure to consider medication effects on stone formation 3
• Inadequate metabolic evaluation: Missing underlying metabolic disorders that contribute to recurrent stone formation 1

Understanding these causes is essential for developing effective prevention strategies and reducing the risk of recurrent kidney stones.