"Pregnant women - especially those with allergies - should be aware that their diet during pregnancy can affect their child's chances of developing eczema and/or food allergies."
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Vaginal delivery and breast-feeding diminish the incidence of allergy and asthma in children up to the age of 18 years, according to new research.
"This is one of the largest cohorts of its kind in the country - it's a longitudinal study," said David Hill, MD, PhD, from the Children's Hospital of Philadelphia. "It's not a snapshot in time in a child's life."
Hill and his colleagues compared the records of 158,422 children to see how the method birth and feeding practice influenced the number of allergic conditions reported by each young person over a period of 18 years.
We have studies looking at the effect of breast-feeding or birth method for a single condition, Hill he told Medscape Medical News, "but we wanted to know the risk of progression throughout the allergic march. We wanted to see the compounded degree of morbidity and, in some cases, mortality because of these characteristics in early life."
Hill presented results from the study - which looked at atopic dermatitis, IgE-mediated food allergy, allergic rhinitis, and asthma - at American College of Allergy, Asthma & Immunology 2019 Annual Scientific Meeting in Houston.
After adjusting for race and sex, the team calculated hazard ratios to determine influence of birth mode (vaginal vs cesarean) and feeding (breast-fed, bottle-fed, or a combination of the two).
Children delivered vaginally had reduced rates of one, two, three, and four allergic conditions (hazard ratio [HR], 0.89, 0.83, 0.84, 0.79, respectively; P = .001).
"The benefits of vaginal delivery were quite broad," Hill reported. The protective effect for those who would develop one condition and for those who would develop all four was reduced for this group.
"It's not very often that a family can decide how a child is delivered," he acknowledged. "But this does tell us something about risk stratification. If a pediatrician has a child that was delivered by C section, they are at higher risk for allergic conditions."
The protective effect likely has something to do with the microbiome, he added. "I think there's some pretty good evidence now - from animal models and associations in humans - to suggest that the birth canal is probably the source of microbial introduction."
Children who were exclusively breast-fed had a reduced rate of one, two, and three conditions (HR, 0.74, 0.75, 0.89, respectively; P = .001).
Children who were fed a combination of breast milk and formula had a reduced rate of one allergic condition (HR, 0.94; P = .001), but no significant difference for two or three conditions. The data were not powered to determine the rate for four conditions.
Supplemental breast-feeding protected against the development of a single allergic condition, but for children who developed two or more conditions, supplemental breast-feeding had no effect.
"Of children who developed two or more conditions, a similar number were supplement-breast-fed and formula-fed," Hill explained. "This effect, of any amount of breast-milk exposure, was a surprise."
Families, for many reasons, might choose to not exclusively breast-feed and might supplement with formula, he pointed out. "They should know this still has a protective effect and could be a modifiable factor."
Hill explained that in his own family, his child could not be breast-fed for as long as recommended. "It is nice to see that even supplemented-breast-fed babies benefit. I was surprised to see the degree of this benefit."
Findings from the Healthy Start Study were also presented at the meeting, by Carina Venter, PhD, RD, from the Children's Hospital Colorado in Aurora.
In their survey of 1315 women, Venter and her colleagues showed that a poor diet during pregnancy combined with a history of allergic disease means that children have a 33% chance of being diagnosed with eczema or food allergy by the age of 2.
"Of the remaining mothers who were classified as having either good dietary diversity, with or without a personal history of allergic disease, or as having poor dietary diversity with no personal history of allergic disease, 21% of their children were diagnosed with eczema and/or food allergy by age 2 years," Venter reported.
"Pregnant women - especially those with allergies - should be aware that their diet during pregnancy can affect their child's chances of developing eczema and/or food allergies" coauthor David Fleischer, MD, also from Children's Hospital Colorado, said in a news release.