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Kidney Stone Fact Page

Most kidney stones are composed of one or more of four compounds: calcium, uric acid, struvite, or cystine.

Calcium stones, particularly those composed of calcium oxalate, are the most common type of stone formed, accounting for 75-85% of all kidney stones. Men are 2 to 3 times more likely to form a calcium oxalate stone than women.

Uric acid stones form when there are too many purine compounds in the body, either from biosynthesis or the diet. The kidneys are not able to excrete the uric acid as quickly as it is created, and the result is that crystals of uric acid accumulate in the kidneys, forming stones. Uric acid stones are often accompanied by the gout, which is caused by uric acid crystals collecting in the body's tissues. About 5-10% of kidney stones are composed of uric acid.

Struvite stones result from a bacterial infection in the urinary tract. The stones are recognized by their "staghorn" appearance. It is important to go on a course of antibiotics if you form this type of stone to kill the infection; otherwise, permanent damage to the urinary tract may result.

Cystine stones are caused by the buildup of the amino acid cystine in the bloodstream, caused by the rare genetic disorder cystinuria.

Kidney stone sufferers should drink enough liquids to generate at least 2 quarts (liters) of urine every day. To make up for evaporative losses, you may need to take in 3 quarts (liters) of fluids daily to generate this much urine.

The February 1, 1996 issue of the American Journal of Epidemiology (Volume 143, Number 3, pages 240-7) contains a paper entitled "Prospective Study of Beverage Use and the Risk of Kidney Stones." These new findings suggest that tea and coffee may actually reduce the chances of forming a kidney stone, while apple and grapefruit juice may increase the risk of forming a kidney stone. If you're a stone former and a tea or coffee drinker and don't want to give up the habit, talk to your doctor about t his study. Still a culprit: cola beverages. Because of their high sugar content, they tend to increase calcium excretion, increasing your risk.

A study similar to the one above by the Harvard School of Public Health has indicated that a higher calcium intake from food sources (not in the form of supplement pills) may decrease the risk of forming stones. This research goes against the common advice to limit calcium intake to prevent kidney stones. The explanation for this phenomenon may be due to the interaction of calcium and oxalate ions in the intestines during digestion. If calcium oxalate forms in the intestines, then it may be excreted in the feces instead of the urine, helping to prevent formation of calcium oxalate stones. If you would like to view an article on the web about this study, click here.

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