What’s the link between mental health and allergies?

Earlier research has shown that people with allergies are more likely to have at least one mental health condition. There is an elevated incidence of depression, schizophrenia, and anxiety among people with atopic dermatitis (AD), for example. Asthma and allergic rhinitis, or “hay fever,” have been linked with schizophrenia, depression, and bipolar disorder.

A new study of data from the UK Biobank confirms the correlation between allergies and mental health. However, correlation does not imply causation, and the study also finds it unlikely that allergies cause mental health conditions or vice versa.

The researchers used Mendelian randomization to investigate possible gene-level causal relationships between mental health disorders and allergies in general — as well as asthma, AD, and hay fever, specifically.

These mental health conditions included depression, major depressive disorder, anxiety, bipolar disorder, schizophrenia, and neuroticism. The researchers concluded, “We did not find evidence of causal effects between allergic disease genetic risk and mental health.”

Senior study author Dr. Hannah Sallis, a senior research associate in genetic epidemiology at Bristol Medical School, explains that the study ultimately utilized a variety of methodologies and data to reach its conclusions. “This helps to strengthen our confidence in the findings. Establishing whether allergic disease causes mental health problems, or vice versa, is important to ensure that resources and treatment strategies are targeted appropriately.”

The study has been published in the journal Clinical and Experimental Allergy.

The team analyzed data in the in the UK Biobank from individuals aged 37–73 years. However, all were of European ethnicity, so the study’s results may not apply to everyone.

The authors acknowledge another limitation, that “Phenotypic analyses were restricted to older adults, so findings may not generalize to younger populations.”

 

Study does not rule out causal connection

While this study only found weak, statistically insignificant indications of causal relationships, this does not rule them out entirely. According to lead study author Dr. Ashley Budu-Aggrey, also a senior research associate at Bristol Medical School: “Our research does not rule out a potential causal effect upon the progression of disease, which is yet to be investigated and could help uncover novel treatment strategies for allergic disease or mental health traits.”

The researchers do note a few possible causal mechanisms that might have escaped their analysis.

Visible skin lesions or itching could lead to social consequences that might exacerbate mental health conditions. And sleep deprivation due to allergy discomfort could similarly affect a person’s mental health.

The study also cites the “inflammatory hypothesis,” which proposes that mental health conditions might arise from the immune system’s inflammatory response to allergies.

Tonya Twinders, the CEO of the Allergy & Asthma Network, who was not involved in the present research, mentioned an earlier study in an interview with Medical News Today.

This suggested that a possible shared mechanism might be “psychological distress, which is central to the etiology of psychiatric disorders but can also give rise to allergies.”

The observational associations

The researchers found that allergies correlated in different ways with mental health conditions, as follows:

Depression: The study confirmed a strong correlation between self-reported depression, major depressive disorder, and allergies in general. Asthma, AD, and hay fever were also strongly associated with depression.

Anxiety: Allergies in general were associated with anxiety, with a stronger correlation for AD than for asthma or hay fever.

Bipolar disorder: Asthma was linked with bipolar disorder, as were allergies in general.

Schizophrenia: The only allergy associated with schizophrenia was hay fever. The effect, however, was protective, meaning that people with hay fever were less likely to have schizophrenia.

Neuroticism: Allergies in general, asthma, and AD were linked with neuroticism. Hay fever was also associated with neuroticism, to a lesser extent.

The study concludes that “Few of the observed associations between allergic disease and mental health were replicated [in the causal investigation].

“The causal effect we did identify appears to be much lower in magnitude than that suggested observationally,” note the authors.

Twinders told MNT: “Intervening to prevent [the] onset of allergic disease is unlikely to directly improve mental health (and vice versa). Future work should investigate whether interventions that aim to improve allergic disease show stronger evidence of a causal effect on mental health (and vice versa).”

Source:medicalnewstoday.com

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