Kidney stones form when high levels of acids or salts within the kidney crystallize. Although kidney stones usually do not cause any lasting harm, passing a kidney stone can be excruciatingly painful. It is important to know the mineral composition of a kidney stone, because it guides the measures that a patient can take to minimize the risk of more stones forming and bringing on another painful episode.
Calcium Oxalate Stones
The Mayo Clinic says that calcium stones are the most common type of kidney stones; some occurring as calcium phosphate but more often as calcium oxalate. Calcium oxalate stones tend to form when the urine is acidic, with a low pH, while calcium phosphate stones tend to form when the urine is alkaline, with a high pH.
Oxalate Sources
The National Institute of Diabetes and Digestive and Kidney Diseases, NIDDK, recommends that people with calcium oxalate stones avoid foods with naturally high concentrations of oxalate like Swiss chard, beets, spinach, sweet potatoes, wheat germ and soy. Nuts, chocolate, dark colas, tea, coffee, cranberry juice, grapefruit juice all contain significant levels of oxalate. The NIDDK also recommends limited intake of foods with significant but lower levels of oxalate, including raspberries, strawberries, grapes, celery, green peppers, grits and liver. In addition to these dietary sources, the liver naturally produces oxalate as well. Vitamin C, or ascorbate, turns into oxalate in the body so people with calcium oxalate stones should limit vitamin C to a maximum of 500 mg per day, according to the NIDDK.
Calcium Sources
People with calcium oxalate stones should continue eating calcium rich foods, because new research shows that they do not increase the risk of calcium stones. In fact, the NIDDK cites evidence that a diet high in calcium-rich foods can actually help prevent formation of calcium stones. Calcium binds to oxalate in the intestines to prevent it from leaching into the blood and eventually reaching the kidneys.
Medical Conditions
Chronic bowel inflammation or intestinal bypass surgery affect the intestinal absorption of calcium, shuttling more to the blood and then urine, increasing the risk of forming calcium stones. Hyperparathyroidism causes too much calcium to circulate in the blood, increasing the risk of stone formation. A rare, inherited metabolic disorder called hyperoxaluria causes over-production of oxalate, increasing the risk of calcium oxalate stones.
Medications
People with calcium oxalate stones might benefit from thiazide diuretics that tip the balance of calcium storage from blood to bone, lowering levels that reach the urine. Rarely, doctors prescribe a drug called sodium cellulose phosphate that takes up calcium in the intestines so that it does not reach the urine.
Alternative Medicine
Although not supported by good medical evidence, drinking black or green tea is a popular herbal remedy for preventing kidney stones. However, the Mayo Clinic cautions that tea contains a significant concentration of oxalate. For people with calcium oxalate kidney stones, drinking tea might actually be harmful rather than helpful in preventing a recurrence.
