Pregnant women often avoid (or at least limit) some of the foods they'd normally like to eat because of the chance those menu items could hurt the health of their baby. In many cases it’s the right thing to do, but women who fear that eating peanuts during pregnancy could cause their child to one day develop a peanut allergy needn't worry, according to a Boston Children's Hospital study.
"Our study showed that increased peanut consumption by pregnant mothers who weren’t themselves nut-allergic was associated with lower risk of peanut allergy in their children," says senior author Michael Young, MD, of Boston Children's Allergy and Immunology Division. "Assuming she isn't allergic to peanuts, there's no reason for a pregnant woman to avoid peanuts." The study was recently published by the Journal of the American Medical Association Pediatrics.
With the great rise of food allergic children and life-threatening reactions in the 1990s, many doctors began advising women to avoid highly allergenic foods like peanuts, nuts and shellfish during pregnancy and while nursing. Pediatricians also advised parents not to give peanuts to any child younger than 3 years old. These recommendations were based on the hypothesis that exposing a young, immature immune system to highly allergenic foods increased the risk of sensitization and could lead to the development of allergy.
Simply put: It was believed that parents should wait until the child's immune system is old enough to handle peanuts, so that the child would have an easier time tolerating them.
Despite the lack of studies supporting this hypothesis, the American Academy of Pediatrics (AAP) endorsed the practice in 2000. In spite of these dietary policies in practice from 1997 to 2007, the number of peanut allergy cases tripled in the U.S., causing the medical community to rethink its guidelines. Based on the lack of evidence supporting early dietary avoidance, the AAP rescinded the recommendation in 2008.
"No one can say for sure if the avoidance recommendation for peanuts was related to the rising number of peanut allergies seen in the late 1990s and early 2000s, but one thing is certain: It didn't stop the increase," Young says. "It was clear that a new approach was needed, opening the door for new research."
To further assess the relationship between a mother's diet during pregnancy and the development of food allergy in her children, Young and his team analyzed large amounts of data provided by The Growing UP Today Study (GUTS). With GUTS data collected from 1990 to 1994, the team looked at the records of more than 8,000 children and positively identified 140 cases of peanut or tree nut allergies. They then examined the diets of their mothers during the pregnancy and afterwards—specifically, if they ate nuts or not—and compared those with the diets of other pregnant women whose children did not develop a peanut allergy.
The team found that the rate of peanut allergy was significantly lower in children whose mothers ate peanuts during and right after pregnancy. While this is a substantial finding, Young is quick to point out that this link can only be described as an association, not a cause-and-effect relationship.
"At this point, the data are not strong enough to prove that eating more peanuts during pregnancy will prevent a peanut allergy," Young says. "But we can say that eating peanuts during pregnancy doesn’t cause peanut allergy in children. So for women who aren’t allergic to nuts, you can eat peanuts while you’re pregnant. It won't increase your baby's likelihood of developing a nut allergy."
Most diet and allergy studies are retrospective in nature, which means they ask the participants to remember specific details about their diet during a given time period, often years later. This type of data collection makes the information vulnerable to memory biases of the participants and other problems. But because the data analyzed by Young and his team was collected through GUTS—an ongoing prospective study, which gathered diet information during or shortly after pregnancy and not years later, it was unaffected by memory issues, providing more accurate data than you'd see in most diet studies.
And unlike other studies that look at the timing of peanut exposure and food allergy, many focusing on the baby’s diet, this is the first time maternal diet during pregnancy has been associated with a lower risk of developing an allergy.
"By linking a mother's peanut eating to a reduced risk of allergy in her children, we are providing new and relevant data to support the idea that early allergen exposure increases tolerance and reduces the risk of developing childhood food allergy," Young says. "With peanut allergies remaining a public health concern for so many families, we're hopeful these findings will lead to a better understanding of this important topic."