Family allergies? Keep nuts away from baby.

Allergies to nuts figure prominently in the growing number of potentially life-threatening sensitivities to foods. A study now suggests that much of the problem may stem from the recent trend of feeding peanut butter and other nutty foods to very young children.

What makes this practice particularly worrisome, notes Wesley Burks of Arkansas Children's Hospital in Little Rock, is that unlike most childhood food allergies-to milk, eggs, soy, or wheat, for example-allergies to peanuts (a legume) or to true nuts tend to persist into adulthood. Preventing these allergies in young children, therefore, may safeguard susceptible individuals from a lifetime of reactions.

In attempting to understand how and why these especially persistent sensitivities develop, Pamela W. Ewan of the Medical Research Council Centre in Cambridge, England, studied the backgrounds and allergies of all 62 nut-sensitive patients, age 11 months to 53 years, referred to her over a year.

Peanuts proved the commonest cause of nut allergy, occurring in 76 percent of the patients, Ewan reports in the April 27 British Medical Journal. Brazil nuts, at 30 percent, provoked the second largest number of cases, followed by almonds, hazelnuts, and walnuts. Allergists had thought peanuts and true nuts are so far apart botanically that sensitivity to one would not increase the likelihood of sensitivity to the other. Ewan found, however, that among the 40 percent of patients sensitive to more than one type of nuts, most were sensitive to peanuts.

In 92 percent of the cases, nut allergies developed by age 7-and usually by age 3. Explains Hugh A. Sampson of Johns Hopkins University School of Medicine in Baltimore, "We think the maturation of the immune system and its ability [to tolerate novel substances] is not well established at a very young age.

That's why more food allergies occur in the first couple years of life."

Peanuts triggered all cases of nut allergies in children less than 12 months old and 82 percent of those in children under age 3. Ewan points out that "some children reacted to the first known exposure to peanuts, suggesting previous sensitization"-perhaps from breast milk or trace amounts of peanuts in cereals or other foods.

Finally, Ewan observed that among nut-allergy patients, almost all were allergic to other allergens, such as cat dander, pollen, or dust mites. She suggests that "peanut and nut allergy is occurring in a subpopulation with a strong propensity to develop allergies." She concludes that in families where allergies are common, keeping true nuts and peanuts from children, "possibly to the age of 7 years, would be justified."

Though such a ban "has scientific validity, I'm not sure it's practical," says John W. Yunginger of the Mayo Clinic in Rochester, Minn. It's because peanut butter is so tasty and nutritious, he notes, that "most American kids get fed a peanut butter and jelly sandwich long before they're a year old."

In an editorial accompanying Ewan's study, Sampson recommends that breast-feeding mothers in families with allergies should avoid eating peanuts.

He argues that these families should also keep foods with true nuts or peanuts from their children until at least age 3. Unfortunately, he concedes, it's not easy identifying which foods contain nuts. Toward that end, he calls on the medical community to "put pressure on governmental agencies" for clear labeling of any foods that contain even traces of peanuts or true nuts.