Kidney stones, also known as urinary calculi, are mineral particles that form in the kidneys or upper urinary tract. Urinary calculi first develop as microscopic crystals that precipitate in urine when the concentration of ions -- calcium, oxalate, uric acid, phosphate or sodium -- increases to the point that these ions can no longer remain in solution. Like hailstones, they grow by accumulating successive mineral layers until they are large enough to cause symptoms, the most noteworthy being pain. Your dietary habits may increase your risk for kidney stone formation.
A Common Condition
Experts at the University of Kansas report that kidney stones affect 1 in 20 Americans sometime during their lives, and 1 in 100 will have a kidney stone in any given year. Men are twice as likely to develop kidney stones as women, and 80 percent of people who have had a kidney stone will have a recurrence within 10 years. Many recurrent stones can be prevented by modifying the diet -- limiting chocolate and other sources of oxalates -- and increasing fluid intake.
Stone Types
According to "The Merck Manual of Diagnosis and Therapy," 80 percent of kidney stones in the United States contain calcium. Most of these are composed of calcium oxalate, with a smaller percentage being calcium phosphate. Uric acid stones -- more common in people with gout -- comprise around 10 percent; cystine stones make up approximately 1 percent; and struvite, a combination of magnesium, ammonium and phosphate, accounts for the remainder.
Risk Factors
Kidney stone formation depends on urinary acidity, volume and concentration. Restriction of fluid intake increases your risk for forming a stone. Because some causes of kidney stones are hereditary, if relative has had a stone, your risk is higher. Chronic vitamin D overdose can lead to kidney stone formation, as can high dietary intake of oxalate-containing foods, such as chocolate, spinach, beets, rhubarb, tea, wheat germ, strawberries and nuts. Cancer, immune disorders, hyperthyroidism, hyperparathyroidism and kidney disorders can all increase your risk for kidney stones.
Considerations and Recommendations
Most recurrent kidney stones can be prevented. The majority of stones in the United States are composed of calcium oxalate. Although your body makes and excretes some oxalate, restriction of oxalate-containing foods, including chocolate, has been shown to reduce urinary oxalate levels and help prevent kidney stones. Restriction of dietary calcium may actually increase your risk of oxalate stones, as calcium binds oxalate in your intestine and prevents its absorption. Increasing your fluid intake to produce at least 2 quarts of urine daily is one of the most valuable preventive measures.
References
- "American Family Physician"; Medical Management of Common Urinary Calculi; P.K. Pietrow, M.E. Karellas; July 2006
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Urinary Calculi"; Mark H. Beers, M.D., Editor-in-Chief; 2006
- "Journal of the American Dietetic Association"; Effect of Dietary Oxalate and Calcium on Urinary Oxalate and Risk of Formation of Calcium Oxalate Kidney Stones; L.K. Massey, et al.; August 1993
