The formation of a stone in the kidneys or urinary tract can be a painful and distressing experience. The majority of kidney stones form as a result of the buildup of calcium, oxalate and phosphate in the kidneys. Other more rare types of kidney stones are formed from amino acids as a result of certain genetic disorders. Understanding the composition of a kidney stone is important in both the treatment and prevention of kidney stones.
Calcium
The National Institute of Diabetes and Dietary and Kidney Diseases (NIDDK) explains that about 80% of all kidney stones result from a buildup of calcium together with dietary compounds in the kidneys and urinary tract over time. Eventually, large calcium deposits can escape from the kidney and travel through the narrow urinary tract, causing tremendous pain. As you may remember from high school chemistry, acid can promote the precipitation of calcium. Acid in the urine similarly plays a role in precipitating calcium in the kidneys to form kidney stones. The NIDDK also explains that individuals with acidic urine, such as diabetics and the obese, are at a greater risk for kidney stones as insulin resistance causes the urine to become more acidic. Interestingly, diets low in calcium may put individuals at risk for developing calcium kidney stones. The use of calcium supplements, however, may increase kidney stone risk.
Oxalate
Calcium kidney stones are almost always found to contain oxalate, a compound from leafy green food sources. Oxalate-rich foods such as spinach, beets, chard, squash, soy crackers, chocolate and certain teas can increase risk of calcium kidney stones. The Oxalosis and Hyperoxaluria Foundation recommends that individuals at risk for calcium kidney stones avoid oxalate-rich foods.
Phosphate
The NIDDK explains that calcium can also combine with phosphate from the diet in the GI or urinary tract to form calcium phosphate. This form of calcium readily precipitates from the urine, especially under acidic conditions. While phosphate is often found in kidney stones, it is rare to develop a stone containing only calcium phosphate without any oxalate.
Cystine
A very rare form of kidney stone results from a genetic defect in the metabolism of the amino acid cystine. According to the Mayo Clinic, individuals that inherit genes that are not capable of processing cystine for excretion build up high levels of this amino acid in their urinary tract. As the concentration of cystine in the kidneys and urinary tract increases, stones form containing mainly cystine. It is recommended that individuals at risk for these stones limit protein intake and drink at least 12 glasses of water per day.
