It seemed like a good idea at the time: With the incidence of peanut allergy climbing among children, the American Academy of Pediatrics in 2000 advised parents to keep peanuts far, far away from infants and toddlers who might have a life-threatening reaction to them.

But a new study suggests that advice did more harm than good. A long-awaited clinical trial found that small children who avoided peanuts for the first five years of their lives were up to seven times more likely to wind up with peanut allergy than kids who made a point of eating peanuts at least three times a week.

Among questions that remain: How much peanut protein do kids need to eat to reduce their allergy risk? Will the protective effect wear off if kids stop eating peanuts?

The findings were presented Monday at the annual meeting of the American Academy of Allergy, Asthma, and Immunology and published online by the New England Journal of Medicine.

“The results have the potential to transform how we approach food allergy prevention,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. The NIAID helped fund the study.

The trial results offer fresh support for the so-called hygiene hypothesis, which ties the recent rise in allergies and autoimmune disorders to the ultra-sterile environment made possible by antibacterial soap, disinfectants and other cleansers that have become staples of modern life. In fact, a study published Monday in the journal Pediatrics found that children whose families used dishwashing machines were more likely to have allergies than kids whose plates were washed by hand.

ROBBING IMMUNE SYSTEM

All of this unnatural cleanliness robs the immune system of the opportunity to develop resistance to germs and other substances that humans used to encounter on a regular basis. The result is less immune tolerance – and more allergies. About 3 percent of children in developed countries are now allergic to peanuts, the study authors say.

Anecdotal evidence for the hygiene hypothesis came from a 2008 study of Jewish children. Some lived in the United Kingdom, where toddlers don’t eat peanuts until they are at least a year old. The others lived in Israel, where infants start eating foods made with peanuts when they are 7 months old. Although both groups of children had a “similar genetic background,” the U.K. children were 10 times more likely to have peanut allergy than their counterparts in Israel.

Some of the doctors and allergy experts who worked on that study set out to test the hygiene hypothesis in a more systematic way. So they enrolled 640 infants in the Learning Early about Peanut Allergy trial – nicknamed LEAP. All of the infants were deemed to be at risk of developing peanut allergy because they were already allergic to eggs and/or they had a severe case of eczema, a skin condition that can be caused by allergies. All of the infants were between the ages of 4 and 11 months when they joined the study.

Researchers conducted a skin-prick test to see if the infants had any sensitivity to peanuts at the start of the study. Then they were randomly assigned to either consume at least 6 grams of peanut protein per week – in the form of a snack food called Bamba or as smooth peanut butter – or to avoid peanuts altogether. All but 10 of the children stuck with the study until they were 5 years old.

The researchers examined the kids in two groups – the 85 percent who had no sensitivity to peanuts at the start of the study and the 15 percent who were already developing peanut allergy. In both groups, the results were striking.

MANY QUESTIONS REMAIN

Among the kids with no sign of peanut allergy at the start of the trial, 13.7 percent of those who avoided peanuts became allergic by the time they turned 5. But among the children who ate peanuts regularly, only 1.9 percent became allergic. That amounted to an 86 percent relative reduction in peanut allergy risk, the study authors found.

Peanut exposure was also helpful for kids who were already on the road to peanut allergy. Among these 5-year-olds, the allergy rate for those who avoided peanuts was 35.3 percent, compared with only 10.6 percent for those who ate peanuts. That worked out to a 70 percent relative reduction in allergy risk, according to the study.

The American Academy of Pediatrics has already withdrawn its endorsement of peanut avoidance. And in the years after the study of Jewish children was published, researchers reported similar findings about allergies to eggs and cow’s milk.

Many questions remain, however. Among them: How much peanut protein do kids need to eat to reduce their allergy risk? Will the protective effect wear off if kids stop eating peanuts? The researchers plan to find out by tracking the study participants through a study they have dubbed LEAP-On.

In the meantime, two pediatric allergy specialists suggest that infants at risk for peanut allergy should try a similar regimen of peanut exposure.

“The results of this trial are so compelling, and the problem of the increasing prevalence of peanut allergy so alarming, new guidelines should be forthcoming very soon,” they wrote in the New England Journal of Medicine. “The LEAP study makes it clear that we can do something now to reverse the increasing prevalence of peanut allergy.”