Kidney stones may develop because people spend too long sleeping in one position. Researchers at the University of California at San Francisco studied 110 patients with recurrent nephrolithiasis (Journal of Urology 2001;165:1085-7) to see whether any relation existed between sleep posture and formation of renal stones. They used a questionnaire to evaluate patients' sleep posture and correlated the side of stone formation with individuals' preference.
In the 93 patients who consistently slept to one side, the side in which renal stones were found was identical to the dependent sleep side in 76%. The positive predictive values of sleep posture and ipsilateral stone formation was 82% for "right side down" and right sided stones and 70% for left side down and left sided stones.
Renal stones are relatively common, affecting up to 15% of people in the United States. Men tend to get kidney stones more than women, and the peak incidence is in the 40-50 age group. The condition can be asymptomatic or extremely painful, resulting in renal colic. While most renal stones pass without incident, some may get stuck in the ureters and urinary tract to cause obstruction, hydronephrosis, and renal failure. Known predisposers to stone formation are metabolic abnormalities such as increased calcium states such as hyperparathyrodism, vitamin D toxicosis, and sarcoidosis. Dehydration, hypercalicuria, cystinuria, hyperuricemia, and infection with various bacteria, such as Proteus , can also lead to stone formation, the latter via inducing changes in pH which allow crystals to form.
The study suggests that sleeping posture has a role in recurrent kidney stone formation because blood flow may be sluggish to the dependent position, allowing crystals to precipitate.Simple behavioural adjustments, such as frequent changes in position while sleeping, may reduce recurrent ipsilateral nephrolithiasis.