Cranberries come from a small evergreen shrub that grows throughout North America. Native American Indian tribes have used cranberry for treating urinary conditions. The tart red fruit is used in cranberry juice, cranberry juice cocktail, jelly and sauce. Research on how cranberry affects kidney stones has shown conflicting results.
Cranberry Fruit
Cranberry fruit, which is used to make all other cranberry products, is high in antioxidants. Substances called proanthocyanidins are the antioxidants that give cranberries their bright red color. Antioxidants help neutralize molecules in the body called free radicals, which damage cell membranes and affect DNA. Cranberries contain large amounts of oxalate, a chemical that is a component of the most common type of kidney stone.
Kidney Stones
Kidney stones form when urinary components -- fluid, minerals and acids -- are out of balance. Increased crystal-forming substances, such as calcium, oxalate and uric acid, cannot be diluted by the available fluid, and if the natural preventive substances in the urine are low, a kidney stone can form. According to the Mayo Clinic, most kidney stones are formed of calcium oxalate. Other less common types of stones are struvite, uric acid and cysteine.
Research
The research on cranberry products has used cranberry juice or cranberry extract rather than cranberry fruit. A study in the "British Journal of Urology International" found that cranberry juice increased the excretion of both calcium and oxalate and concluded that cranberry juice could decrease the incidence of calcium oxalate kidney stones. However, a report in the January 2001 issue of "Urology" noted that cranberry extract increased urine oxalate and could be a factor in causing kidney stones.
Recommendations About Cranberry
According to Medline Plus, drinking more than 1 liter of cranberry juice a day for a long period of time may increase the risk of getting kidney stones. The University of Maryland warns that taking cranberry supplements or drinking large amounts of cranberry juice can increase the risk of developing kidney stones. Dr. Darren Lynch, writing in the December 2004 "American Family Physician," states that doctors should be cautious in using cranberry products over the long term in patients who tend to form oxalate stones.
Further Considerations
In some situations, cranberries -- in any form -- may be helpful for kidney stones. But potential risks exist if you have calcium oxalate stones. If you have a history of kidney stones, consult a health care professional before using cranberry products.
References
- "Urology"; Dietary Supplementation With Cranberry Concentrate Tablets May Increase the Risk of Nephrolithiasis; M.K. Terris, et al.; January 2001
- "American Family Physician"; Cranberry for Prevention of Urinary Tract Infections; Darren M. Lynch, MD; December 2004
- "British Journal of Urology"; Influence of Cranberry Juice on the Urinary Risk Factors for Calcium Oxalate Kidney Stone Formation; T. McHarg, et al.; November 2003
- University of Maryland Medical Center; Cranberry Steven D. Ehrlich, NMD; November 2008
- Mayo Clinic; Kidney Stones; April 2011
