Kidney stones affect as many as 10 percent of Americans at some point in their lives, according to the National Institutes of Health. Most people who have stones once will have them again. Calcium oxalate forms in the intestines from the combination of two minerals, calcium and oxalate. Calcium and oxalate form kidney stones; the two substances do not dissolve stones, either together or separately. Calcium oxalate stones comprise the largest group of kidney stones.
How Stones Form
Calcium oxalate stones form when too much oxalate passes through the kidneys. Oxalate binds to calcium in the intestine. When you have lower than normal calcium levels, less oxalate is bound and more passes through the kidneys. Eating foods containing large amounts of oxalate can also result in larger than normal levels of oxalate passing through the kidneys. Decreased fluid intake also increases the risk of developing kidney stones, since more concentrated urine causes mineral to precipitate or form crystals. Around 25 percent of people have a family history of kidney stone formation, so genetics may also play a part, according to NetWellness.
Reducing Calcium
Reducing calcium does not prevent calcium oxalate stones, because oxalate needs calcium to bind to so it can be removed from your body. Reducing calcium can worsen rather than reduce your risk of kidney stones. Your doctor may suggest raising your calcium levels slightly by increasing your calcium intake rather than reducing your intake.
Reducing Oxalate
Reducing oxalate, on the other hand, may help prevent calcium oxalate stone formation and may also prevent excess calcium loss, which could damage bones. Consuming large amounts of oxalates will cause oxalates to bind with calcium and prevent calcium from being absorbed. Eight foods contain the highest amounts of oxalate, according to gastroenterologist Frank Jackson, M.D. of Jackson/ Siegelbaum Gastroenterology. Foods high in oxalate include rhubarb, beets, strawberries, chocolate, wheat bran, spinach, nuts and tea. Draft beer, tofu, legumes and sweet potatoes also contain large amounts of oxalate. Some doctors recommend reducing oxalate intake to 50mg per day, Dr. Jackson says. Ask your doctor if reducing oxalates in your diet will help with your kidney stones.
Considerations
Protein can also increase both calcium and oxalate levels. Vitamin C intake produces oxalate, according to Dr. Jackson. Your doctor may suggest not taking supplements that contain vitamin C. Increasing fluid intake may help prevent stone formation, but avoid tea, a substance very high in oxalates, if you tend to form stones. Drink 12 full glasses of fluid per day to help wash out stones if they form, the NIDDK recommends.
References
- National Institute of Diabetes and Digestive and Kidney Dieases; What I Need To Know About Kidney Stones; April 2007
- Jackson/ Siegelbaum Gastroenterology; Kidney Stone Diet; Frank Jackson, M.D.
- University of Michigan: Dietary Changes to Prevent Calcium Oxalate Stones
- HealthCommunities.com; Kidney Stones Overview; April 2011
- NetWellness; Kidney Stones; Martin Resnick, M.D., et al.; September 2009
