Medical researchers appear to be one step closer to conquering potentially deadly peanut allergies. At a scientific meeting this week, they're reporting on an experimental treatment that has freed a small number of children from their allergies.

More than 3 million Americans are allergic to peanuts or tree nuts, such as walnuts, and, for reasons that aren't clear, the number seems to be rising. About half of the 150 deaths caused by food allergies in the U.S. each year are caused by peanut allergies.

Only 20 percent of children with peanut allergies outgrow them. The rest must stay vigilant, bringing their own food to parties and avoiding restaurants if they can't be sure the menu is "peanut-safe." An allergic response usually strikes within minutes of exposure.

The new therapy works similarly to allergy shots, which haven't proved safe against food allergies. Exposure to increasing amounts of peanut flour gradually builds up tolerance. Blood tests show that the immune system begins to ignore the peanut flour instead of attacking it.

Researchers caution that the treatment shouldn't be tried outside a research study in which subjects are closely monitored.

Children start with the lowest dose of peanut flour they can take without a reaction — just one one-thousandth of a peanut in some cases, said Wesley Burks, chief of pediatric allergy at Duke University. Duke is collaborating on the research with the Arkansas Children's Hospital.

SUPERVISED STUDY

The children go home with measured daily doses for two weeks and then return for tests and two weeks of slightly larger doses to be mixed in food. In one study, subjects ate flour equal to 15 peanuts a day after eight to 10 months of this. Nine of 33 have or had been on that maintenance dose for 2 1/2 years.

After "challenges" in which they were asked to eat peanuts, four of the nine were declared ready to stop treatment.

For now, at least, those four still must eat peanuts every day. Other studies have shown that "as long as you keep something in your diet, your tolerance stays," Burks said adding that the procedure should not be tried without medical supervision.

The researchers also are conducting a trial in which 10 children were randomly assigned to get either peanut flour or a placebo flour.

After a year, all five who had been getting peanut flour could tolerate a challenge of about 13 peanuts; those on placebo could tolerate only one peanut.

"Within the next five years, I think we're going to have some active therapy for food allergy," said Burks' collaborator, Stacie Jones of Arkansas Children's Hospital.