Urinary stones, technically called urinary calculi, can occur anywhere in the urinary tract, in humans most commonly in the kidneys and ureters. (In dogs the deposits form most often in the bladder.) Urinary stones develop when crystallized salts and minerals form a hard mass in the upper urinary tract.
Kidney stones are hard masses that form when the crystals separate from the urine and accumulate in the hollow parts (pelvis or calyces) that drain the kidneys. The stones often pass out of the body in the urine, but can be incredibly painful during the passage. Sometimes the stones settle in the urinary system and continue to grow. blocking the flow of urine, making urination painful or impossible. Urinary tract infections, certain kidney and metabolic disorders and excessive vitamin D intake are among the triggers of stone formation. But often, it is unclear why a person develops kidney stones. Most kidney stones contain calcium oxalate, which has led to the mistaken belief that stone sufferers must avoid all dairy products to keep urinary calcium levels low. Too often, serious calcium restriction can result in bone loss and the fractures that accompany osteoporosis.
About 80% of the time, kidney stones manage to pass through and out of the urinary tract on their own. Those which do not pass on their own can be broken up with ultrasound, or removed with an instrument inserted through a tiny surgical incision. Fewer than 5% of sufferers require surgery. There is a significant recurrence rate once an individual has produced the first stone. Without preventative tactics, about 50 to 60% of patients will have a second attack within 10 years; with adherence to preventative measures, a second attack can be averted in over 96% of cases.
Most afflicted are adults living in affluent, industrialized countries. Stones are associated with a diet rich in animal protein and low in liquids. A typical kidney stone patient is a man 20 to 50 years old, as men are three to four times as likely to form stones as are women. One woman in 20 and one man in 7 in the USA can expect to experience the pain of kidney stones at least once before reaching 70. Particularly at risk are joggers and other active people who do not drink enough, women who deliberately limit their fluid intake, and travellers who are afraid of the local water supply.
Many patients form kidney stones on one side of the body. If the components of urine were the major factor in their stone formation, stones would logically occur on both sides of the body. In a 2-year study of 110 patients who suffered from stones on one side of the body, researchers found that patients' stones frequently recurred on the side they favoured during sleep. Of the 93 patients who consistently slept on one side, three-quarters had their kidney stones on that side. This study suggests that sleep position plays a role - possibly by affecting blood flow to the kidneys. Temporary slow-downs in circulation to the kidneys may affect the organs' ability to clear itself of various substances, the report indicates.