Do allergies increase the risk of mental illness? New study finds no causal link
A new study may provide some comfort to those with allergies. Research has found little evidence that having allergies directly increases the risk of developing mental health problems, or vice versa, which previous research had suggested might be the case. While it’s still possible that treating allergies could improve the mental state of some people, there doesn’t appear to be a cause-and-effect relationship between allergy to something and mental illness, the researchers say.
Allergies and mental health issues like depression or severe anxiety are diseases plentiful for mankind. Some studies have suggested that people diagnosed with either are more likely to be diagnosed with each other. Based on this observational data, the scientists argued that there might be underlying risk factors common to both, and / or that developing one of these conditions (usually allergies) predisposes us to each other. For example, people with allergies have overactive immune responses to their triggers, leading to symptoms caused by inflammation. And chronic inflammation is also thought play some role in mental illness.
A common refrain in science, however, is that correlation is not necessarily equal to causation. Unfortunately, it is not always possible to conduct randomized, controlled experiments that may show a causal link, such as clinical trials used to show that a drug works. But researchers have other methods of trying to disentangle the causes and effects of large population studies. One of these methods is known as Mendelian randomization, which is based on the study of genetic biomarkers in people, variations in genes believed to increase our risk for a certain disease.
Researchers at the University of Bristol turned to data from UK Biobank, a long-term project launched in 2007 that collected data from genetic information (anonymous) of 500,000 volunteers in the country who have been monitoring their state of health ever since. They focused on whether having genetic biomarkers for allergy or mental illness was linked to a higher risk of being diagnosed with the other. Because a person’s genes can’t be affected by unrelated outside factors, any link you find is more likely to represent a true cause and effect, according to study author Ashley Budu-Aggrey, epidemiologist. and medical geneticist in Bristol.
As other studies have done, Budu-Aggrey and his team found a strong association between the diagnosis of allergic diseases like asthma and mental health problems like depression. But they found only very weak evidence of a genetic link between allergies and mental illness in either direction, indicating that there is no overall causal relationship., especially for allergies causing mental illness. The results of the study were published Wednesday in Clinical and Experimental Allergy.
“Our results suggest that the risk of allergic disease does not increase the risk of mental health problems,” Budu-Aggrey said.
Like all research, study has its limits. Apart from genetic data, many information collected from volunteers about their health is self-reported, so there is always the possibility of misreporting. And they found a stronger genetic link between hay fever and bipolar disorder, suggesting there may be a direct relationship between these two diseases in particular.
Another caveat is that the team only focused on whether the onset of allergic disease could increase the risk of subsequent mental illness. But it’s always possible that an allergy that goes untreated or gets worse over time could have a direct impact on a person’s risk of mental illness. Conversely, as some research has suggested, successfully treating a severe allergy could improve a person’s mental health.
The authors say these are all questions future studies should explore. And Mendelian randomization in general should be used more widely by researchers to help address questions about cause-and-effect relationships raised by other observational studies, Budu-Aggrey said. Previous studies using this method have raised doubts about the presumed fear that cannabis use causes schizophrenia, as well as supported the theory that being more educated can increase our risk of myopia.
Ultimately, however, the results suggest that it will not be possible to kill two birds with one stone in this particular case. Preventing mental illness and allergies are two laudable goals, but we probably shouldn’t expect to achieve one by attacking the other, according to Budu-Aggrey.
“Interventions to prevent allergic disease are unlikely to improve mental health,” she said.