Children with autism are nearly twice as likely to have any allergic condition than those without autism, researchers found.
A significant and positive association has linked common allergic conditions to autism spectrum disorder (ASD) in children.
According to a new study conducted by a research team at the University of Iowa College of Public Health, the odds ratio (OR) of ASD increased in children also diagnosed with food allergy, respiratory allergy, and skin allergy.
Led by Guifeng Xu, of the college’s Epidemiology department, researchers conducted a population-based, cross-sectional study of data provided by the National Health Interview Survey (NHIS) from 1997-2016. The analysis featured 199,520 children aged from 3-17 years old (mean age 10.21 years).
ASD has become an increasingly prevalent condition among US children, researchers noted, increasing from 0.67% of the population in 2000 to 1.46% in 2012. Though there’s still limited understanding of its definite pathology, clinicians have indicated some driving factors.
“The etiology of ASD involves both genetic and environmental risk factors, and it is estimated that up to 40% to 50% of variance in ASD liability might be attributed to environmental risk factors,” researchers wrote.
Other symptoms, such as immunologic dysfunction, may be to explain the link between environmental risk factor and ASD — researchers noted frequent infections and prevalence of autoimmune conditions is common in children with ASD.
To discern the relationship between allergic conditions and ASD, researchers defined the former category as children having reported in the past 12 months a food or digestive allergy; any respiratory allergy; or eczema or other skin allergies in the NHIS data. ASD was defined by physicians’ diagnoses, per the survey.
Adjusting for age, sex, race or ethnicity, family education level, family income, and geographic region, researchers estimated for ORs and 95% confidence intervals (CIs) of ASD according to allergic condition presence, as those factors have been associated with both conditions.
Observed children were a majority boys (51.47%) and predominately non-Hispanic white (48.72%). Hispanic (27.8%), non-Hispanic black (15.42%) and other races (8.06%) comprised the remaining population. For weighted prevalence of allergies, researchers distinguished the observed population of having 4.31% for food allergy, 12.15% for skin allergy, and 9.91% for skin allergy.
An ASD diagnosis was reported in 1868 children, reporting a 0.95% weighted prevalence (95% CI; 0.89 — 1.01). Children with ASD were more likely to have a food allergy (11.25% versus 4.25%), respiratory allergy (18.73% versus 12.08%), and skin allergy (16.81% versus 9.84%) than those without in every weighted prevalence (P < 0.001). After adjusting for the above listed factors, the OR of ASD among children with food allergy was nearly tripled (OR 2.72; 95% CI; 2.26 — 3.28; P < 0.001).
The OR was lower, though still statistically significant, of ASD among children with respiratory allergy (OR 1.53; 95% CI; 1.32 — 1.78) and skin allergy (OR 1.80; 95% CI; 1.55 – 2.09; P < 0.001). Overall, the adjusted OR of ASD was 1.82 among children with any allergic condition versus those without.
Researchers noted the association between food allergy and ASD remained significant in all patient subgroups for age, sex, and race or ethnicity. Though little is known about the link between food allergy and ASD — and research has more focused on skin or respiratory allergies — they recalled the results of the Childhood Autism Risks From Genetics and the Environment (CHARGE) study that suggested even food sensitivities may be more common in children with ASD.
There’s also been an increasing prevalence of both conditions in recent years, as both have become more common in the past 2 decades. Though the mechanisms linking the 2 are unclear, researchers pointed to the “gut-brain-behavior axis” as a key factor.
“Previous studies found higher prevalence of gastrointestinal symptoms among children with ASD,” researchers wrote. “Food allergy may involve alterations in the gut microbiome, allergic immune activation, and impaired brain function through neuroimmune interactions, which may finally affect the enteric nervous system and central nervous system leading to neurodevelopmental abnormalities.”
That said, confirmation from prospective cohort analysis would be necessary to conclude this distinct association.
“The underlying mechanisms for the association of food allergy and other allergic conditions with ASD remain to be elucidated,” researchers wrote.
The study, "Association of Food Allergy and Other Allergic Conditions With Autism Spectrum Disorder in Children," was published online in JAMA this week.