Which of the following is the most common cause of nephrolithiasis?

Decreased fluid intake is the most common cause of nephrolithiasis, or kidney stones. Insufficient fluid intake leads to concentrated urine, which promotes the crystallization of minerals and salts, specifically calcium oxalate and uric acid, facilitating stone formation. When urine volume is low, solutes have a higher chance of reaching concentrations that exceed their solubility limits, resulting in precipitation and stone growth.

While increased calcium intake, a high sodium diet, and smoking may also play roles in the development of kidney stones, they are not the primary factors. For example, while high sodium intake can lead to increased calcium excretion in urine, the direct relationship of inadequate hydration with stone formation is much more significant. Hydration helps dilute the urine, reducing the likelihood of stone formation, which is why maintaining adequate fluid intake is crucial in preventing nephrolithiasis.