What Causes Kidney Stones?
A kidney stone is a hard mass developed from crystals that separate from the urine within the urinary tract. Normally, urine contains chemicals that prevent or inhibit the crystals from forming. These inhibitors do not seem to work for everyone, however, so some people form stones. If the crystals remain tiny enough, they will travel through the urinary tract and pass out of the body in the urine without being noticed.
Kidney stones may contain various combinations of chemicals. The most common type of stone contains calcium in combination with either oxalate or phosphate. These chemicals are part of a person’s normal diet and make up important parts of the body, such as bones and muscles.
Doctors do not always know what causes a stone to form. While certain foods may promote stone formation in people who are susceptible, scientists do not believe that eating any specific food causes stones to form in people who are not susceptible.
The leading cause of kidney stones is a lack of water. Stones commonly have been found in those that drink less than the recommended eight to ten glasses of water a day. When there is not enough water to dilute the uric acid (component of urine), the pH level within the kidneys drops and becomes more acidic. An excessively acidic environment in the kidneys is conducive to the formation of kidney stones.
A person with a family history of kidney stones may be more likely to develop stones. Urinary tract infections, kidney disorders such as cystic kidney diseases, and certain metabolic disorders such as hyperparathyroidism are also linked to stone formation. In addition, more than 70 percent of people with a rare hereditary disease called renal tubular acidosis develop kidney stones.
Cystinuria and hyperoxaluria are two other rare, inherited metabolic disorders that often cause kidney stones. In cystinuria too much of the amino acid cystine which does not dissolve in urine is voided, leading to the formation of stones made of cystine. In patients with hyperoxaluria the body produces too much oxalate, a salt. When the urine contains more oxalate than can be dissolved the crystals settle out and form stones.
Hypercalciuria is inherited and it may be the cause of stones in more than half of patients. Calcium is absorbed from food in excess and is lost into the urine. This high level of calcium in the urine causes crystals of calcium oxalate or calcium phosphate to form in the kidneys or elsewhere in the urinary tract.
Other causes of kidney stones are hyperuricosuria, which is a disorder of uric acid metabolism, gout, excess intake of vitamin D, urinary tract infections, and blockage of the urinary tract. Certain diuretics, commonly called water pills and calcium-based antacids may increase the risk of forming kidney stones by increasing the amount of calcium in the urine.
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