Exposure to higher levels of allergens during infancy results in lower asthma risk

Naveed Saleh, MD, MS, for MDLinx | May 08, 2018

Among high-risk inner city children, exposure to higher indoor levels of pet or pest allergens during infancy was associated with lower risk of asthma, according to a recent study published in the Journal of Allergy and Immunology.

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Among children living in urban environments, increased levels of pet and pest allergens were associated with reduced risk of asthma at 7 years of age.

“In this report, we examine exposures in the prenatal period and first 3 years of life, including allergens and microbes in house dust, as potential risk factors for asthma at age 7 years,” wrote lead author George T. O’Connor, MD, MS, Department of Medicine, Boston University School of Medicine, Boston, MA.

Environmental exposures play an important role in childhood asthma; however, experts have yet to elucidate modifiable risk factors for this illness.

“Childhood asthma is associated with sensitization to inhalant allergens, whereas the effect of early-life exposure to these allergens or their sources on asthma risk is unclear and might differ among allergens,” wrote the authors. “Increased early-life exposure to microbial products, such as bacterial endotoxin, appears to be associated with reduced susceptibility to atopic asthma in childhood.”

The Urban Environment and Childhood Asthma (URECA) Study is a birth cohort study that started in 2005 in inner-city areas of Baltimore, Boston, New York City, and St. Louis. The researchers recruited pregnant women aged 18 and older in which the woman herself or the father had a history of asthma, allergic rhinitis, or eczema. In total, 442 children were included in this report.

The researchers collected the following data from children and parents during annual clinical visits to the study center and periodic follow-up:

  • Body measurements
  • Blood tests
  • Responses to maternal and postnatal questionnaires
  • Parent-reported colds documented by phone
  • Blood tests to determine levels of allergen-specific IgEs in children
  • Pulmonary function tests in children
  • Home visits to gather environmental data and specimens

The primary outcome for this study was childhood development of asthma at age 7 years. The researchers used logistic regression to assess relationships between demographic, perinatal, and family factors whereas environmental exposures were adjusted for sex, race, maternal asthma, and maternal stress.

Among children living in urban environments, increased levels of pet and pest allergens were associated with reduced risk of asthma at 7 years of age.

“A number of bacterial taxa differed in abundance in the homes of children who did and did not have asthma,” wrote the authors, “and most of these taxa were also significantly associated with cockroach, mouse, or cat allergens.”

The researchers also found that the indoor bacterial microbiome was associated with either decreased or increased asthma risk. Specifically, they used 16S ribosomal RNA sequencing to identify 202 bacterial taxa that were significantly more abundant in households of children with asthma and 171 bacterial taxa that were significantly less abundant in these households.

Prenatal smoking exposure, higher maternal stress, and maternal depression also increased asthma risk.

“Our findings suggest that primary prevention strategies for childhood asthma in low-income urban communities should probably not focus on home allergen reduction and that exposure to a broad variety of proteins in early life might have health benefits with respect to asthma,” conclude the researchers. “Interventions to reduce prenatal smoking and reduce maternal stress and depression during pregnancy and infancy might hold promise for asthma prevention.”

To read more about this study, click here

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