Does Cranberry Juice Prevent Kidney Stones?

Kidney stones are made of certain substances that precipitate out of the urine, forming large crystals. Larger kidney stones may get stuck in the kidney or the ureter, which is the tube that carries urine from the kidney to the bladder. The most common type of kidney stone is made of calcium combined with either oxalate or phosphate; but other stones may occur, including those made of uric acid or struvite. Drinking cranberry juice, which prevents bacteria from sticking to cells lining your urinary tract, according to MedlinePlus, may be useful in preventing kidney stones, but more research is needed.

Glass of cranberry juice and cranberries (Image: HandmadePictures/iStock/Getty Images)

Causes of Kidney Stone Formation

Your diet contains some of the substances that cause kidney stone formation, such as oxalic acid and calcium. Fruits, vegetables and grains contain oxalic acid, or oxalate. Stone formation is also the result of uric acid, a by-product of protein digestion. As these substances become concentrated in the urinary tract, hard stones or crystals form. Your body produces natural inhibitors to stone formation, but they sometimes fail, according to NYU Langone Medical Center.

Calcium Oxalate Stones

The New York University School of Medicine defines hyperuricosuria as high levels of uric acid in urine. Hyperuricosuria can cause calcium stone formation. According to an article by Lynda Frassetto, M.D. and Ingrid Kohlstadt, M.D., M.P.H., published in the Dec. 1, 2011 issue of "American Family Physician," cranberry juice increases urine acidity and should be avoided to prevent formation of calcium oxalate stones. Frassetto and Kohlstadt suggest increasing urine alkalinity by eating fruits and vegetables, drinking alkaline mineral waters.

Struvite Stones

Struvite stones contain magnesium, ammonium, phosphate and calcium carbonate. They form as the result of a bacterial infection that produces ammonia. Ammonia increases urine alkalinity. According Frassetto and Kohlstadt, acidic urine prevents struvite stone formation. Cranberry juice lowers urine pH, the measurement used to determine acidity or alkalinity, without causing the problems associated with acidic foods, such as the problem commonly called heartburn.

Recommendations

The University of Maryland Medical Center recommends not drinking cranberry juice if you are susceptible to calcium oxalate stones, but increasing fluid intake, including cranberry juice, to treat struvite stones. Because it contains oxalate, cranberry juice should be avoided by stone formers, according to the National Kidney and Urologic Diseases Information Clearinghouse. To prevent additional kidney stone formation, NYU Langone Medical Center notes that your doctor may recommend drinking more cranberry juice. These conflicting recommendations indicate that no final conclusion has been reached about the benefits of cranberry juice as a treatment modality for prevention of kidney stones. The University of Maryland Medical Center suggests, if you have kidney stones, consult your doctor before self-treating with cranberry juice or cranberry supplements.

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