Fluid Intake

• Most patients with kidney stones are advised to increase their fluid intake to encourage a natural passing. Since coffee is a natural diuretic, it is highly effective at raising urinary volume for this purpose.
  
  

Hormonal Influence

• In a Harvard study, it was speculated that the caffeine in coffee interferes with the creation of a urine-reducing hormone. As a result, the body produces more urine that prevents formation of kidney stones.
  
  

Magnesium and Citrate

• Caffeinated coffee has also been observed to elevate of levels magnesium and citrate in urine; these components are believed to counteract kidney-stone-causing minerals.
  
  

Calcium

• Since kidney stones are primarily composed of calcium, some researchers note that the increased levels of magnesium and citrate are not significant enough to offset the effects of calcium-rich urine.
  
  

Facilitating Properties

• Caffeine also has been observed to facilitate the production of calcium and sodium. Urine rich in calcium and sodium can lead to the growth of kidney stones.