Although kidney stones can occur in anyone, they are most common in adults over the age of 40, according to the Mayo Clinic. Kidney stones--small crystallized pebbles of minerals and acid salts--form in the kidneys when urine becomes concentrated or when levels of minerals and salts get too high. They can grow to several millimeters in diameter and cause extreme pain when they block the kidney or travel through the ureter. Several factors contribute to the formation and growth of kidney stones in adults.
Dietary Factors
Diets high in sugars, sodium and proteins encourage the formation and growth of stones because they contribute to the risk of dehydration. According to the Mayo Clinic, most kidney stones consist of crystallized calcium oxalate. A diet heavy in oxalate-rich foods such as beets, okra, spinach, sweet potatoes, nuts and chocolate can contribute to the development of calcium oxalate stones.
Dehydration
Dehydration lowers the volume of urine, concentrating any salts and minerals in the kidneys and creating an environment conducive to the formation of kidney stones. The Mayo Clinic says that doctors often advise people with a history of kidney stones to eliminate about 2.6 quarts of urine per day to keep the system in balance, and to increase their intake of water until their urine output reaches that goal.
Supplements
Large doses of vitamin D increase the body's absorption of calcium and can contribute to the formation of calcium oxalate stones. Your doctor might recommend that you stop taking calcium supplements, or take them only with meals to reduce their impact on your kidneys. According to the Merck Manual, high doses of vitamin C can also cause formation of calcium oxalate stones.
Genetics
Some people might be genetically predisposed to develop uric acid kidney stones. People with a close relative who had a kidney stone have an increased risk of having a kidney stone too. The Merck Manual says that 50 percent of men and 75 percent of women who have calcium oxalate stones have a hereditary disorder called hypercalciuria. People with an inherited disease called cystinuria excrete too much of the amino acid cysteine into the urine, causing formation of cystine stones.
Medical Conditions
Medical conditions that interfere with the absorption of calcium, such as inflammatory bowel disease or gastric bypass surgery, increase the risk of kidney stones. People with kidney disease or urinary tract infections cannot efficiently flush excess minerals and salts from the kidneys, raising their risk for kidney stones. A hyperactive parathyroid gland--hyperparathyroidism--throws off calcium levels and can trigger formation of calcium oxalate stones.
