Kidney stones are one of the most common disorders of the urinary tract. They are an ancient health problem. Evidence of kidney stones has been found in an Egyptian mummy estimated to be more than 7,000 years old.
At this time, studies suggest that kidney stones affect more than 5% of Americans, and the rate has increased since the 1970s.
Gender and Age
Men. Kidney stones are more common in men than women. The risk of kidney stones increases in men in their 40s and continues to rise until age 70. Caucasian men have a higher risk than other ethnic groups.
Women. The risk of kidney stones peaks in a woman's 50s. In younger women, stones are more likely to develop during the late stages of pregnancy. Pregnant women tend to have a higher calcium intake, but their kidneys do not handle the calcium as well as they did before pregnancy. Kidney stones are still rare during pregnancy, however, affecting only 1 in 1,500 pregnancies.
Risk Factors in Children. Stones in the urinary tract in children are usually due to genetic factors. Most of the time, the cause is too much calcium in the urine (hypercalciuria). Deformities in the urinary tract pose a significant risk for kidney stones in children. Babies born at a low birth weight who need to be fed intravenously are also at risk for stones.
Obesity and Weight Gain
Obesity and weight gain are both associated with an increased risk for kidney stones.
Higher BMIs and larger waist circumferences are both risk factors for kidney stones. Researchers think that there may be a link between fat tissue, insulin resistance, and urine composition. People with larger body sizes may excrete more calcium and uric acid into the urine, which increases the risk for kidney stone formation.
A family history of kidney stones increases one's risk for the condition. Researchers are looking into genetic markers or other factors that might predict the risk of kidney stones in relatives, although none has yet been clearly identified. A family history of gout may also make a person more vulnerable to developing stones.
Caucasians seem to have the highest incidence of kidney stones, followed by Mexican Americans. African-Americans have the lowest risk.
Dietary factors, minerals in local water, or both may contribute to geographic differences that have been observed in the occurrence of kidney stones. Studies have reported the highest occurrence of kidney stones in the southern region of the United States and the lowest occurrence in the west.
Specific Foods. In general, certain foods increase the risk for stones, but only in people who have a genetic or medical vulnerability. People whose diets are high in animal protein and low in fiber and fluids may be at higher risk for stones. A number of foods contain oxalic acid, but there is no proof that such foods make any major contribution to calcium oxalate stones in people who do not have other risk factors. However, several studies have shown that increasing dietary calcium and restricting salt, animal protein, and foods rich in oxalate can help prevent calcium oxalate stones from returning.
Stress. One study reported that people who had a major, stressful life experience were more likely to develop stones than those who had not had a stressful experience. Some experts speculate that this increased risk may be due to a hormone called vasopressin, which is released in response to stress. Vasopressin also increases the concentration of urine.
Being Bedridden. Any medical or physical condition that keeps a person in bed or immobile increases blood levels of calcium from bone breakdown, thereby posing a risk for stone formation.
Gout. Patients with gout are at high risk for uric acid stones.
High Blood Pressure. People with high blood pressure are up to three times more likely to develop kidney stones. It is not entirely clear whether having high blood pressure increases the risk for a stone, stones lead to high blood pressure, or there is an action linking both conditions.
Inflammatory Bowel Disease. Crohn's disease and ulcerative colitis cause problems in the absorption of substances in the intestines. These problems significantly increase the risk for kidney stones, particularly in men.
Urinary Tract Infections. Urinary tract infections (UTIs) are almost always the cause of struvite stones.
Hyperparathyroidism. The parathyroid glands regulate calcium levels in the body through parathyroid hormone. In hyperparathyroidism, one or more of these glands makes too much parathyroid hormone. Some people with hyperparathyroidism develop kidney stones. Surgery to remove the hyperactive parathyroid gland in such patients reduces the risk for stone formation, but the risk still remains high for some time after surgery.
Other Medical Conditions. Kidney disease, chronic diarrhea, certain cancers (such as leukemia and lymphoma), and sarcoidosis (swelling around the organs) put people at higher risk for stones.
AIDS medications. More than 10% of AIDS patients who take the medicine indinavir develop stones. The risk is even higher in people with AIDS who also have hepatitis B, hepatitis C, or hemophilia, as well as those who are very thin or who take the antibiotic combination TMP-SMX.
Other Drugs. Kidney stones are a rare side effect of thyroid hormones and loop diuretics (drugs that increase urination), although diuretics are also used to prevent calcium stones. Certain cancer chemotherapy drugs can also cause kidney stones. Long-term use of medications such as antacids, which change the acid content of urine, may increase the risk for kidney stones.