A surge in celiac disease cases among babies and toddlers in Sweden was not related to childhood vaccinations, a new study finds.

Celiac disease is a digestive disorder caused by an abnormal immune response to gluten, a protein in wheat, rye and barley. The disease damages structures in the lining of the small intestine, which then interferes with the body's absorption of nutrients.

Particular gene variants may make people susceptible to celiac disease. But researchers are still studying the environmental factors that influence whether certain people develop the disorder, while others do not.

Between 1984 and 1996, Sweden saw an "epidemic" of celiac disease among children younger than two - a sudden four-fold increase in the normal rate of the disorder. Overall, celiac disease is thought to affect about one percent of the population.

The Swedish epidemic ended just as abruptly. And since then, researchers have been trying to figure out why.

In theory, infant vaccines could play a role in celiac disease. Since they stimulate the immune system, it's possible that in certain children, vaccines could trigger an abnormal response to gluten.

But that's just a theory. And the new study, reported in the journal Pediatrics, doesn't bear it out.

Researchers found that changes in Sweden's national vaccine program did not correlate with the timing of the celiac disease epidemic. In fact, the introduction of pertussis vaccination (against whooping cough) corresponded to a decline in celiac.

And when the researchers compared children with celiac against kids without it, they found no link between vaccination and the risk of having the disorder.

"This was a nice study, a very careful study," said Dr. Joseph A. Murray, who directs the celiac disease program at the Mayo Clinic in Rochester, Minnesota, and was not involved in the research.

"It goes a long way toward showing that vaccinations do not explain the celiac epidemic in Sweden," Murray told Reuters Health.

So what does explain it?

Based on past studies, changes in infant nutrition may partly account for it, said Dr. Anna Myleus, who led the new work.

Understanding what caused Sweden's spike in early celiac disease - and the drop-off a decade later - could help with celiac prevention in general, Myleus told Reuters Health in an email.

The "important message" from this study, she said, is that childhood vaccinations do not appear to be risk factors for celiac disease.

Sweden's sudden surge in early-life celiac was unusual. There has been no similar pattern among U.S. babies and toddlers, Murray said.

It's thought that infant feeding may go far in explaining Sweden's epidemic, according to Murray. For a time, it became popular for parents to use "follow-on" formulas that contained milk and a large amount of wheat, to wean babies from regular infant formula.

Murray noted that England and Ireland had spikes in early-life celiac disease back in the late-1960s to 1970s. That seemed to be related to parents' habit of giving babies cereal very early, he said; after health campaigns telling parents to hold off on cereal until the age of five to six months, early celiac cases declined.

These days, experts generally recommend exclusive breastfeeding until the age of six months, when rice cereal and other solid foods can be introduced.

The current findings are based on information from Sweden's national register on childhood celiac cases. Myleus and her colleagues looked at whether changes in the country's childhood vaccination program corresponded to the beginning or end of the 1984-1996 epidemic.

The researchers also compared 392 babies with celiac disease against 623 celiac-free babies the same age, living in the same area of Sweden.

Overall, changes in the national vaccine program did not match up with the timing of the epidemic, the researchers found. And there was no evidence that babies who developed celiac differed from other infants in rates of vaccination against pertussis, measles-mumps-rubella or H. influenza type B.

The one exception was the finding that babies vaccinated against tuberculosis had a lower risk of celiac. But that does not necessarily mean the vaccine, known as BCG, is protective, the researchers say.

In Sweden, the BCG vaccine is given only to children at increased risk of tuberculosis - largely immigrants. And they may have a lower celiac risk for different reasons.

In the U.S., there's been no "epidemic" of celiac among babies. But the overall rate of the disease has increased, Murray said.

In a 2009 study, he and his colleagues found that celiac disease may be four times more common in the U.S. today than in the 1950s. Similar increases have been reported in Europe.

Although celiac disease is thought to affect one percent of the population, Murray said about 30 percent of Americans may carry genes that make them susceptible.

The reasons for the overall increase in celiac are not clear, but Murray said that factors related to gluten must be involved.

People may, for example, be eating more gluten now than they used to. And in someone with a genetic predisposition, that could tip them toward an abnormal immune system reaction.

It's also possible that changes in the processing of gluten-rich foods could have a role, Murray speculated.

"I think it's crucially important to determine why there is more celiac disease today," he said.

The only treatment for celiac disease is to follow a lifelong gluten-free diet. For most people, sticking with the diet prevents symptoms, like abdominal pain, bloating and diarrhea, and allows damage to the small intestine to heal.

But gluten-free products generally cost more than standard varieties. And Murray said there is no need to cast gluten as a general villain, to be avoided by everyone.

If you think you might have celiac disease, he said, get tested before putting yourself on a gluten-free diet.