To the great surprise of parents, kidney stones, once considered a disorder of middle age, are now showing up in children as young as 5 or 6.
While there are no reliable data on the number of cases, pediatric urologists and nephrologists across the country say they are seeing a steep rise in young patients. Some hospitals have opened pediatric kidney stone clinics.
“The older doctors would say in the ’70s and ’80s, they’d see a kid with a stone once every few months,” said Dr. Caleb P. Nelson, a urology instructor at Harvard Medical School who is co-director of the new kidney stone center at Children’s Hospital Boston. “Now we see kids once a week or less.”
Dr. John C. Pope IV, an associate professor of urologic surgery and pediatrics at the Monroe Carell Jr. Children’s Hospital at Vanderbilt in Nashville, said, “When we tell parents, most say they’ve never heard of a kid with a kidney stone and think something is terribly wrong with their child.”
In China recently, many children who drank milk tainted with melamine — a toxic chemical illegally added to watered-down milk to inflate the protein count — developed kidney stones.
The increase in the United States is attributed to a host of factors, including a food additive that is both legal and ubiquitous: salt.
Though most of the research on kidney stones comes from adult studies, experts believe it can be applied to children. Those studies have found that dietary factors are the leading cause of kidney stones, which are crystallizations of several substances in the urine. Stones form when these substances become too concentrated.
Forty to 65 percent of kidney stones are formed when oxalate, a byproduct of certain foods, binds to calcium in the urine. (Other common types include calcium phosphate stones and uric acid stones.) And the two biggest risk factors for this binding process are not drinking enough fluids and eating too much salt; both increase the amount of calcium and oxalate in the urine.
Excess salt has to be excreted through the kidneys, but salt binds to calcium on its way out, creating a greater concentration of calcium in the urine and the kidneys.
Interesting, but not too surprising, especially when you consider how much soda kids drink, the rise in childhood obesity, inadequate water intake, and the link all of these have with kidney disease.