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The relationship between bacteria and mental illness

“The nose has been formed to bear spectacles – thus we have spectacles.” Voltaire, “Candide.”

Not unlike Candide, scientists search for cause and effect relationships in nature. For years, researchers have sought organic causes for mental illness. New research into schizophrenia lends credence to the belief that some mental illnesses are rooted in natural causes.

Candida albicans

Research headed up by Emily G. Severance of John Hopkins University School of Medicine studied the link between this variety of fungi and bipolar disorder and schizophrenia. The pathogen, Candida albicans, produces the antibodies, IgG, that cause yeast infections. Severance and her research team examined 947 subjects. Of them, 260 had schizophrenia, 270 had bipolar disorder, 170 had first-episode schizophrenia and the remainder had no history of mental illness.

Initially, the researchers found no difference in IgG levels in the test and control groups. When they categorized groups by sex, they found higher levels in males with bipolar or schizophrenia compared to the control group. In females with schizophrenia, higher levels IgG resulted in lower cognitive function compared to females with schizophrenia with no antibodies. The results were tabulated using the Repeatable Battery for the Assessment of Neuropsychological Status.

Severance and her team note more research is required to establish a direct link between IgG antibodies and bipolar disorder or schizophrenia. “It’s far too early to single out Candida infection as a cause of mental illness or vice versa,” she says. Severance believes initial results are encouraging because this type of infection is easily treated in early stages and its presence in patients with mental illness can provide physicians with a diagnostic roadmap.

Gut-brain connection

Severance’s research adds to the scientific literature on gut-brain connection and mental illness. Researchers looking for a gut-brain connection to autism discovered mice showing signs of autism had higher levels of 4-ethylphenylsulphate (4EPS). Researchers believe this chemical is produced by gut bacteria.

Similar research into children with autism found low levels of Bacteroides fragilis, a microorganism found in the intestines. Researchers gave the microorganism to mice displaying behavior similar to autism. They found the bacteria altered the rodents’ microbiome (collective genome of microbes living inside the body). They also found the introduction of the bacteria changed the animals’ behavior. Their anxiety decreased; they interacted with the other mice; and they showed a marked decrease in repetitive behavior.

ENS and psychobiotics

Scientists describe the enteric nervous system (ENS) as the second brain. The ENS governs the digestive system. It communicates with the brain via neurons. Anyone with irritable bowel syndrome (IBS) or other gastrointestinal disorders will readily attest the torments of the brain are visited upon the digestive system. Researchers at University College Cork in Ireland found that mice raised in germ-free environments lacked the ability to recognize other mice. The Irish researchers also found when a mouse’s microbiome is no longer homeostatic, it displays behavior similar to human anxiety, depression and autism.

As mentioned above, scientists received results when they injected mice with 4EPS. The Cork scientists believe that by developing similar compounds, which they call psychobiotics, can be instrumental in treating individuals with certain types of mental illness. Unlike mice, humans would receive the benign bacteria from a regulated diet.

While the connection between bacteria and mental illness is still tentative, the link between substance abuse and mental illness is unequivocal. According to the Substance Abuse and Mental Health Services Administration, in 2014, nearly 8 million Americans had co-occurring mental health and substance abuse disorders. Sovereign’s El Paso facility specializes in treating individuals with dual diagnosis. Contact our 24/7 helpline for more information about our treatment programs.

About the author:

Darren Fraser is a content writer for Sovereign Health Group. He worked two and half years as reporter and researcher for The Yomiuri Shimbun until they realized he did not read, speak or write Japanese and fired him. Undeterred, he channels his love of research into unearthing stories that provide hope to those dealing with addiction and mental illness. Darren loves the Montreal Canadiens hockey club and horror films and would prefer to enjoy these from the comforts of his family’s farm in Quebec. For more information about this media, contact the author at


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