Food allergies occur when the body's immune system mistakingly launches an attack in response to harmless proteins in certain foods.
According to Food Allergy Research and Education (FARE), up to 15 million people in the United States have food allergies, including 1 in every 13 children.
Cow's milk, soy, wheat, fish, shellfish, peanuts, and tree nuts account for 90 percent of all allergic reactions to foods in the U.S., with onset of such allergies typically occurring in childhood.
A number of studies have suggested that early childhood exposure to allergenic foods may significantly reduce the risk of developing an allergy to these foods. Others, however, have identified no such link.
While current guidelines for infant feeding no longer advise parents to delay exposing their children to allergenic foods, they do not recommend that such foods be introduced early.
"The implications for preventing food allergy or other immune-mediated health conditions in the general population are not clear," note the study authors, including Dr. Robert J. Boyle, of Imperial College London in the United Kingdom.
Babies fed peanut between 4-11 months at 70 percent lower allergy risk
With this in mind, Dr. Boyle and team decided to conduct a systematic review and meta-analysis of observational studies and intervention trials that assessed the effects of exposure to allergenic foods in a child's first year of life.
Of the 16,289 studies and trials reviewed, the researchers pinpointed 146 that were eligible to be included in the analysis.
Fast facts about food allergy
- Between 1997-2011, children's food allergies in the U.S. rose by around 50 percent
- Children's food allergies cost the U.S. almost $25 billion annually
- Each year, 300,000 ambulatory-care visits occur due to a food allergy reaction among children and teenagers under the age of 18.
Overall, the analysis revealed an association between the age at which a child is first introduced to allergenic foods and the subsequent development of food allergies.
The team identified "moderate-intensity evidence" that introducing egg to the diet of infants between 4-6 months of age reduced the risk of egg allergy by 40 percent, while introducing peanut between 4-11 months may lower peanut allergy risk by 70 percent.
In further detail, the researchers found that in a population where 5.4 percent of people have an egg allergy, introducing egg to an infant between 4-6 months of age could prevent 24 egg allergy cases per 1,000 people.
Additionally, in a population where 2.5 percent of individuals have a peanut allergy, feeding infants peanut between 4-11 months of age may prevent 18 cases of peanut allergy for every 1,000 people, the team reports.
When it came to fish, the researchers identified "low-certainty evidence" that consumption of fish prior to 6-12 months of age lowered the risk of allergic rhinitis, and there was "very low-certainty evidence" that feeding infants fish before the age of 6-9 months reduced the risk of allergic sensitization.
"We were surprised to see no effect for celiac disease, which is a different type of allergy to egg and peanut allergy," Dr. Boyle told Medical News Today. "This suggests that early introduction of allergenic foods does not reduce risk of all types of food allergy."
Findings should inform new infant feeding guidelines
While the study did not investigate the underlying mechanisms of the link between early exposure to egg and peanut and reduced risk of allergy to these foods, Dr. Boyle speculates that it is down the immune properties of the intestine.
"Feeding peanut and egg to infants results in a different immune response to being exposed to small amounts of peanut and egg through different routes, such as touching the skin or being inhaled," Dr. Boyle told MNT.
"We think that if infants are not fed peanut or egg early, they are at risk of becoming allergic to those foods when they are exposed through casual skin or airway contact, sometimes quite indirectly through food antigens present in dust around the home," he added.
The team stresses that further research is needed to determine what form of egg and peanut is best to give to infants, noting that many of the studies reviewed used dried egg powder, which many families might not consume.
Additionally, they caution against feeding whole peanuts or peanut pieces to young babies, as they are a choking hazard.
Still, Dr. Boyle told us that their study results should inform new guidelines on infant feeding practices.
"After reading these new findings, some parents may wish to introduce egg and smooth peanut butter into the diet of their infant at the time when other solid foods are being introduced, since delaying introduction of egg and peanut is likely to increase the risk of allergy to these foods in their infant."
Dr. Robert J. Boyle
"Infants with troublesome eczema or other signs of food allergy would be best advised to see a doctor for advice and consideration of an allergy skin prick test first, since they may already have an allergy to egg or peanut," he added.
Timing of allergenic food introduction to the infant diet and risk of allergic or autoimmune disease: A systematic review and meta-analysis, Robert J. Boyle et al., JAMA, doi: 10.1001/jama.2016.12623, published online 20 September 2016, abstract.
JAMA news release, accessed 20 September 2016.
Imperial College London news release, accessed 20 September 2016.
Additional source: FARE, Facts and statistics, accessed 20 September 2016.