Allergic disease, mental health conditions linked, but relationship likely not causal
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Although there is a link between allergic disease and mental health, this relationship does not appear to be causal, according to a study published in Clinical & Experimental Allergy.
“Previous studies had reported on a relationship between mental health and allergic diseases including asthma, hay fever and eczema, but little was known about the causal relationship,” author Ashley Budu-Aggrey, PhD, senior research associate with the medical research council integrative epidemiology unit at University of Bristol Medical School in Bristol, England, told Healio.
“Given the high prevalence of allergic disease and mental health disorders such as depression and anxiety, this was an important health question to answer,” Budu-Aggrey said. “A true causal relationship could potentially inform clinicians of strategies to reduce the risk for mental health problems or allergic disease.”
The researchers used data from the UK Biobank (UKB) study to investigate the phenotypic associations between allergic disease and mental health.
Using summary data from relevant genome-wide association studies (GWAS), the researchers then performed two-sample Mendelian randomization to explore the causal nature of these associations.
The UKB provided phenotype data for individuals aged 37 to 73 years with asthma, atopic dermatitis and hay fever, as well as with depression, anxiety, bipolar disorder, schizophrenia and neuroticism.
The researchers collected self-reported mental health and allergic disease phenotype data during verbal interviews conducted at the first assessment center.
Published GWAS have identified 89 independent single nucleotide polymorphisms (SNPs) related to the broad allergic disease phenotype, as well as 16 independent SNPs for asthma, 37 for hay fever and 23 for atopic dermatitis.
GWAS also have revealed 32 SNPs for major depressive disorder, 22 for bipolar disorder, five for anxiety, 79 for schizophrenia and 66 for neuroticism.
According to the researchers, there was strong observational evidence for an association between the broad allergic disease phenotype and self-reported depression (OR = 1.45; 95% CI, 1.41-1.5; P = 3.63 × 10-130) and major depressive disorder (OR = 1.4; 95% CI, 1.35-1.46; P = 2.63 × 10-76).
The researchers also report a strong association between depression and the individual asthma, atopic dermatitis and hay fever phenotypes, but with different magnitudes.
Evidence of an association between anxiety and the broad allergic disease phenotype (OR = 1.25; 95% CI, 1.18-1.33; P = 6.45 × 10-13) was found as well, with stronger evidence with atopic dermatitis and weaker associations with asthma and hay fever.
Apparently driven by asthma, the researchers said, bipolar disorder was associated with the broad allergic disease phenotype, but this association was not consistent for hay fever or atopic dermatitis.
Hay fever was the only allergic disease that showed evidence of association with schizophrenia, exhibiting a protective effect (OR = 0.41; 95% CI, 0.23-0.7; P = 1.36 × 10-3).
Also, all allergy phenotypes showed evidence of an association with neuroticism, particularly with the broad allergic disease phenotype, asthma and atopic dermatitis.
Yet the researchers’ two-sample Mendelian randomization turned up little evidence that genetic liability for the broad allergic disease phenotype causally increases the risk for psychiatric traits. They also found little evidence that any of the mental health phenotypes causally affected the broad allergic disease phenotype.
“Observationally, we found strong evidence of a relationship between allergic disease and mental health traits, where having any one of asthma, eczema and hay fever increased the risk for depression, anxiety, bipolar disorder and neuroticism,” said Budu-Aggrey.
“However, the associations for the causal relationship were much weaker and unable to replicate that which was found in the observational analysis. This suggests that the observational relationships found were inflated likely due to confounding or some other form of bias,” she said.
Interventions that prevent the onset of allergic disease are unlikely to directly improve mental health, Budu-Aggrey said, and mental health interventions likely would not improve allergic diseases.
“However, it is important to note that our study was restricted to older adults, so it may not be generalizable to younger populations,” Budu-Aggrey said. “Future work should aim to investigate the causal effect upon disease progression and whether interventions to improve allergic disease could also have an effect upon mental health or vice versa.”
For more information:
Ashley Budu-Aggrey, PhD, can be reached at ashley.budu-aggrey@bristol.ac.uk.