Doctors at Johns Hopkins Medical Institutions in Baltimore and other facilities are finding a curious increase in children with kidney stones -- another possible consequence of America's dependence on processed foods.
Bad eating habits have already fueled twin epidemics of childhood obesity and Type 2 diabetes. Although doctors have blamed fats and sugar for those ills, they say the culprit in this case may be two other features of the fast-food culture: too much salt and not enough water.
Although kidney stones remain uncommon among children, specialists who once treated only a few cases a year are trying to figure out why they are now seeing many times that number.
"Five years ago, we used to see maybe a handful of children a year, maybe five or six," said Dr. Yegappan Lakshmanan, a pediatric urologist at the Johns Hopkins Children's Center. "Now, it's five or six a month. Some are repeat patients, but it's definitely a trend."
Kidney stones, once found almost exclusively in adults, are tiny mineral deposits that can cause excruciating pain when they lodge in the urinary tract.
Three years ago, Hopkins established a pediatric kidney stone clinic after noticing an increase in cases. More recently, the Vanderbilt Children's Hospital in Nashville opened a kidney stone clinic, and the Harvard-affiliated Children's Hospital in Boston is doing the same.
"We feel like we're seeing the same trend," said Dr. Caleb Nelson, a pediatric urologist at Harvard. "Whereas five or 10 years ago, you could go several months between [cases], now we see a couple a week."
Improved methods of diagnosing stones may be one reason for the sudden increase in cases. They might account for larger numbers of children with stones too small to cause symptoms, doctors say, but not what many believe is an increase in children who arrive doubled over in pain.
"In children, we think diet has an important part to play -- a lot of fast food with high salt content," Lakshmanan said.
Too much salt causes people to excrete excessive calcium, which can crystallize in the urine in the form of stones. That problem, Lakshmanan said, is compounded by the tendency of children to skimp on water, which in sufficient quantities can dilute minerals that cause stones.
Quantifying the problem is difficult because childhood kidney stones have never been carefully tracked.
Pediatricians have long known that certain congenital problems -- including blockages in the kidney or bladder -- can cause stones. Additionally, babies treated in intensive care units sometimes get medications that can make them predisposed to stones.
Those factors produced a small caseload, but nothing like the numbers doctors have seen more recently.
Nelson agrees that it's too soon to declare diet the chief culprit, but he believes it's a leading candidate. At Harvard and Hopkins, dietitians are not only advising families about healthy eating habits, but also compiling dietary histories that could help solve the riddle.
"It does make sense that the fatter the country, the more stones you'll see," Nelson said. That doesn't necessarily mean that processed foods are causing kidney stones, he said. Children with kidney stones are more likely to be overweight than youngsters in years past -- but youngsters in general are heavier than they used to be.
Doctors recommend no more than one teaspoon of salt -- or 2.4 grams of sodium -- per day, said Dr. Alicia Neu of the Johns Hopkins clinic. But many Americans, and particularly children, consume much more than that from processed foods.
Youngsters should also drink two liters of water a day, doctors say.