SAN DIEGO – The prevalence of kidney stone disease appears to be rising in the United States.
According to an analysis of responses from the 2007-2012 National Health and Nutrition Examination Survey (NHANES), 8.8% of people in the United States have kidney stone disease (Eur Urol. 2012 Jul;62[1]:160-5), up from a prevalence of 5.2% observed in the 1988-1994 NHANES.
Dr. Anna L. Zisman
“There’s also been a marked increase in emergency room visits for kidney stones: 91% between 1994 and 2006,” Dr. Anna L. Zisman said at the meeting sponsored by the American Society of Nephrology.
“Unfortunately, it doesn’t only affect adults. There has been an increased incidence in ER visits for kids as well.” Though good national data on the incidence of kidney stone disease in children are lacking, one study conducted in South Carolina found that the incidence of ER visits in children rose from 8 per 100,000 in 1996 to more than 18 per 100,000 in 2007 (J Pediatr. 2010 Jul;157[1]:132-7).
What’s driving these increases? Dr. Zisman, a nephrologist at the University of Chicago, discussed a “recipe” for how to create a kidney stone, with heredity as the first step.
“Pick your parents well,” she said. “The familial clustering index is higher for nephrolithiasis than for diabetes and hypertension. A family history of stone disease is present in 16%-37% of stone formers, compared with 4%-12% of healthy controls. And the heritability estimates – how much of a given disease or trait can be attributable to genetic predisposition – is somewhere between 46% and 63%.”
According to Mayo Clinic researchers, heritable traits for kidney stone disease based on 24-hour urine measurements, adjusted for diet, include calcium, magnesium, pH, and citrate (Clin J Am Soc Nephrol. 2014 May;9[5]:943-50).
“Hypercalciuria is the most well-established risk factor for stone disease,” Dr. Zisman said. “Up to 50% of subjects with stones have a history of hypercalciuria, and 43% of first-degree relatives of hypercalciuric patients have hypercalciuria.”
Race and gender are two factors people can’t control in their risk for kidney stone disease. NHANES data suggest that non-Hispanic whites are at highest risk for stone formation, compared with Hispanics and non-Hispanic blacks. However, among whites and all of the racial categories, males have a higher risk than females.
Step two in the recipe for stone formation is timing: Age matters.
According to an analysis of 49,976 men who participated in the Health Professionals Follow-Up Study, the highest risk of stone formation was in male patients in their 40s (J Am Soc Nephrol. 2004 Dec;15[12]:3225-32). By the time white males reach their 70s, the prevalence is almost 19%, while the prevalence for white women in their 70s is 9.4% (Eur Urol. 2012 Jul;62[1]:160-5).
Step three in the recipe is location. According to Dr. Zisman, the prevalence of kidney stone disease across the world is quite varied. “That likely has to do with both genetic predispositions as well as environmental factors,” she noted. “For example, Iran, which has a pretty warm climate, has a prevalence of 5.7%, Greece 15.2%, whereas Argentina only 4%. In the United States, data suggest that the highest incidence of stone disease is in the south. It is suspected that this is due to more men working outside in manual labor in the heat, but that’s just a hypothesis.”
Step four in the recipe involves the role of certain nutrients. For example, a higher daily calcium intake is associated with a lower risk of kidney stone formation. “The theory is that with higher dietary calcium, your urine oxalate tends to drop,” she said. Increased intake of magnesium, protein, potassium, and fluid are also associated with decreased stone formation.
On the other hand, a higher daily vitamin C intake is associated with an increased risk of stone formation. Specifically, a daily intake of more than 1,000 mg confers a 41% increased risk, compared with a lower intake. “The theory there is that vitamin C intake, once absorbed, results in a higher urine oxalate,” Dr. Zisman said.
Current epidemiology literature draws no clear association between a high-sodium diet and the development of kidney stones. From a clinical standpoint, however, “I think everyone would recommend a low-sodium diet because of the physiologic mechanisms leading to higher urine calcium,” she said.
Higher body mass index and increased waist circumference also impact the risk of developing kidney stones, especially among women. “The higher [they are], the greater the risk,” Dr. Zisman said. “We know that as weight goes up, urinary pH drops. Another potential reason is that as body weight goes up, urinary oxalate goes up as well.”