Peanut and tree nut allergies are among the most common food allergies in children and adults, and they're on the rise. A new study suggests moms-to-be could hold the key to preventing them.
Children born to non-allergic mothers who frequently ate nuts during their pregnancies had a lower risk of developing the allergy, researchers from a number of hospitals and universities including Boston Children's Hospital and the Dana-Farber Children's Cancer Center found.
"Our study supports the hypothesis that early allergen exposure increases the likelihood of tolerance and thereby lowers the risk of childhood food allergy," they wrote in a study published in the Journal of the American Medical Association Pediatrics on Monday.
Food allergies manifest when the body's immune system mistakenly perceives a harmless food and attacks it. The resulting symptoms can be relatively mild, such as hives, or potentially life-threatening, in the case of anaphylaxis. Between 1997 and 2011, food allergies among children in the United States increased by roughly 50 percent, for reasons researchers do not fully understand.
Nuts are a particular problem. According to figures cited in this new study, the prevalence of childhood peanut allergies in the U.S. has more than tripled in recent years, jumping from 0.4 percent of children in 1997 to 1.4 percent in 2010. Unlike childhood allergies to eggs and milk, allergies to peanuts and tree nuts, including walnuts, almonds, hazelnuts, cashews and pistachios, are seldom outgrown.
According to the study's authors, previous research conducted on animals regularly found a protective effect resulting from maternal exposure to certain foreign substances during pregnancy and breastfeeding. Similar studies of humans, however, have been far less consistent. One U.K.-based study in the 1990s, for example, found that children under 6 who had peanut allergies were more likely to have moms who ate peanuts during pregnancy or while they were nursing -- the opposite of this study's findings.
To test the potential effect of maternal nut consumption on allergies, the researchers in the new investigation used data on more than 8,200 children whose mothers participated in the Nurses Health Study -- one of the longest-running investigations into women's health in the U.S. -- and compared information on the women's diets with subsequent allergy diagnoses among their children.
Women who had no peanut or tree nut allergies, and who ate nuts five times or more per week during pregnancy, had children with the lowest risk of the allergy.
While the researchers allow that further studies are needed to replicate their findings, they argue that their data supports recent decisions to "rescind recommendations that all mothers avoid [peanut and tree nuts] during pregnancy and breastfeeding." The American Academy of Pediatrics previously recommended that women who were pregnant or breastfeeding avoid peanuts -- a guideline that was nixed in 2008.
But the new findings do not apply to women who are themselves allergic to nuts.
"For women who already have allergies, obviously adding nuts to their diet [during pregnancy] would, absolutely, be the wrong answer," said Dr. Loralei Thornburg, a high-risk pregnancy expert with the University of Rochester Medical Center, who did not work on the study.
Thornburg added that the underlying mechanisms of the link between nut exposure during pregnancy and reduced allergy risk are not yet clear; it could be the exposure to nuts somehow "primes" babies' bodies and tells them that certain foods are safe, or it could simply be that non-allergic babies are born to non-allergic mothers.
"If you're a nut person, I would not avoid nuts during your pregnancy because of fear that it would induce an allergy in your child," Thornburg said, adding that she often advises her patients to eat plain roasted almonds, since they contain no unhealthy additives. "Nuts are a great source of mono-unsaturated fats and folic acid."