What are the risk factors for nephrolithiasis in adults?

Risk Factors for Kidney Stone Formation

The primary risk factors for nephrolithiasis include low urine volume, metabolic abnormalities (hypercalciuria, hypocitraturia, hyperoxaluria, hyperuricosuria), male sex, obesity, diabetes, gout, and specific dietary patterns including low fluid intake, high sodium intake, and excessive animal protein consumption. 1

Demographic and Constitutional Risk Factors

• Male sex is a major risk factor, with lifetime incidence of approximately 13% in men versus 7% in women 1
• Age patterns differ by sex: In males, risk increases until approximately age 53 then decreases (likely related to declining androgen levels), while in females risk continuously rises with aging 2
• Female gender is paradoxically associated with more aggressive recurrent stone disease when first stone episode occurs before age 20 3
• Obesity significantly increases stone risk independent of dietary factors 1
• Family history of nephrolithiasis increases individual risk, reflecting genetic predisposition 4

Metabolic and Biochemical Risk Factors

Approximately 96% of recurrent stone formers have identifiable urinary biochemical abnormalities 4:

• Hypercalciuria (elevated urinary calcium) is present in 60.9% of stone formers and comprises multiple variants including absorptive hypercalciuria Types I and II, renal hypercalciuria, and renal phosphate leak 4
• Hypocitraturia (low urinary citrate <320 mg/day) affects 28-31% of patients, reducing the natural inhibition of calcium oxalate crystallization 1, 4
• Hyperuricosuria (elevated urinary uric acid with normal urine pH) is found in 35.8% of calcium stone formers 4
• Hyperoxaluria (elevated urinary oxalate) occurs in 8.1% and includes enteric, primary, and dietary variants 4
• Low urine pH (<5.5) with normal uric acid excretion characterizes gouty diathesis in 10% of patients 4
• Abnormally acidic urine is the primary driver of uric acid stone formation, more important than hyperuricosuria or low urine volume 5
• Low urine volume (<1 liter/day) is present in 15.3% of stone formers 4

Medical Comorbidities

• Primary hyperparathyroidism increases stone risk through sustained hypercalciuria 1
• Diabetes mellitus is independently associated with increased stone formation 1
• Gout increases risk, with clinical gout frequently present in uric acid stone formers 1, 5
• Metabolic syndrome is nearly universal in uric acid stone formers, characterized by low baseline urine pH and insufficient urinary ammonium buffer production 5
• Intestinal malabsorption and chronic diarrheal syndromes increase risk through enteric hyperoxaluria and metabolic acidosis 1, 5
• Malignancies with high cell turnover predispose to uric acid stones through increased purine metabolism 5
• Anatomical urinary tract abnormalities promote stone formation through urinary stasis 1

Dietary Risk Factors

High-Risk Dietary Patterns

• Low fluid intake producing less than 2 liters of urine daily is a critical modifiable risk factor 1, 6
• High sodium intake (>2,300 mg/day) reduces renal tubular calcium reabsorption, directly increasing urinary calcium excretion 1, 6
• Excessive animal protein (>7 servings of meat/fish/poultry per week) generates sulfuric acid, increasing urinary calcium and uric acid while reducing protective citrate 1, 6, 7
• Sugar-sweetened beverages, especially colas acidified with phosphoric acid, increase stone risk (RR 1.20) 1, 6
• High vitamin C supplementation (≥1,000 mg/day) increases stone risk by 41% (RR 1.41,95% CI 1.11-1.80) as vitamin C metabolizes to oxalate 6, 7
• High oxalate foods (nuts, chocolate, tea, spinach, wheat bran) increase risk particularly in patients with baseline hyperoxaluria 1, 6

Protective Dietary Factors

• Higher dietary calcium intake (1,000-1,200 mg/day from food) paradoxically reduces stone risk by 30-50% by binding intestinal oxalate and preventing its absorption 6, 7
• Higher magnesium intake reduces risk (RR 0.71,95% CI 0.56-0.89) 7
• Higher potassium intake reduces risk (RR 0.54,95% CI 0.42-0.68) by increasing urinary citrate excretion 6, 7

Critical Pitfall to Avoid

Never recommend calcium restriction—this is the most common and dangerous misconception. Low dietary calcium (<400 mg/day) paradoxically increases stone risk by increasing intestinal oxalate absorption and urinary oxalate excretion 1, 6. The age-related protective effect of dietary calcium is strongest in men under 60 years old 7.

Stone Recurrence Risk Factors

• Initial stone episode before age 20 predicts more aggressive disease with higher recurrence rates 3
• Without treatment, 5-year recurrence rate is 35-50% after a symptomatic stone event 1
• Multiple metabolic abnormalities are present in 58.7% of recurrent stone formers, requiring comprehensive evaluation 4