Does growth before baby alter allergy risk in humans?
It is increasingly clear that genetics alone do not explain risks of developing allergies, and that environmental exposures before and around birth can program individuals to increased or decreased risk of allergies. Restricted growth before birth in preclinical studies appears to protect the offspring against allergic responses. However, whether prenatal growth predicts subsequent risk of allergy in humans is unclear. Many studies in humans use birth weight as a measure of fetal growth, but do not correct for gestational age, so effects of premature birth may confound those of fetal growth.
In an article recently published in The Journal of Allergy and Clinical Immunology (JACI), Wooldridge and coauthors report the results of a systematic review assessing the relationship between prenatal growth and allergic disease in humans. They screened more than 15,000 publications from 11 databases and reference lists, and read nearly 1,900 full papers which identified 42 studies that met inclusion criteria. Importantly, they included studies only where birth weight, the most common measure of fetal growth, was corrected for gestational age.
The researchers analyzed the associations between birth weight corrected for gestational age and the incidence of allergic diseases in children and adults. The analyzed studies included over 2.1 million individuals with data for allergic dermatitis, commonly known as eczema, nearly 70,000 people with data on food allergy and over 100,000 people with data for allergic rhinitis or hayfever. Most of the studies were in children from developed countries, and most were European.
The authors found that heavier birth weight was associated with increased risk of food allergy and allergic dermatitis, but not allergic rhinitis, in childhood. Insufficient data were available to assess relationships between fetal growth and allergic asthma, and between fetal growth and incidence of many allergies in adults. The authors’ findings suggest that faster fetal growth, resulting in a baby who is heavy for their gestational age at birth, is a risk factor for some but not all childhood allergies. Given that most of the allergies were assessed in young children, further studies investigating allergies in older children, adolescents and adults are needed to help inform how and when IUGR alters immune development and susceptibility to allergic disease.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.