The association between physical and mental health was first described around 400 B.C. by Hippocrates, known as the father of Western medicine, who theorized that various physical and mental health conditions were due to an imbalance of fluids in the body (i.e., “humors”). Hippocrates theorized that our exposure to various environmental factors could produce an imbalance in any one of the four bodily humors and lead to illness and disease. At the time, a holistic approach — including aspects of diet, exercise and personal hygiene — was used to treat pathological conditions and to improve an individual’s health.
In the early 1900s, Henry Cotton, M.D., an American physician and superintendent of the Trenton State Hospital, was convinced of the notion that focal infection was the primary cause of dementia praecox (i.e., schizophrenia) and manic depression (i.e., bipolar disorder). For several decades, the responsibility of neurotransmitters in the development of mental illness has dominated psychological theories. For example, the dopamine theory of schizophrenia suggests that schizophrenia is caused by the overactivity of the dopamine system in the brain. While these theories have increased researchers’ understanding of the specific changes to neurotransmitters that occur in the brains of people with mental illness, neurotransmitters alone are not the sole cause of mental illness.
In recent years, the body’s ability to fight off infections and disease has resurfaced as an important contributor to the development of different types of mental illness. Schizophrenia, in particular, is a severe mental illness characterized by delusions (i.e., false beliefs), hallucinations (i.e., seeing, hearing or sensing things that are not really there) and cognitive dysfunction that is frequently associated with inflammation and immune system dysfunction in the empirical literature — but schizophrenia is not the only mental illness that has been associated with physical health problems. “Inflammation is a key part of the stress response. It has also been linked to a variety of bodily ills, from diabetes and heart disease to depression and Alzheimer’s disease,” said Kirsten Weir, M.A., a writer from Minneapolis.
Immune system dysfunction and the development of schizophrenia
Schizophrenia has been linked to adverse events during pregnancy — including infections, toxin exposure and maternal stress — as well as immune system dysfunctions and autoimmune diseases. At the same time, schizophrenia is also associated with increased mortality from infectious diseases, such as pneumonia and influenza, across the lifespan, said Brian J. Miller, M.D., Ph.D., M.P.H., an associate professor at Georgia Regents University. Researchers have found that mothers who have the flu during pregnancy increase their child’s risk of developing schizophrenia by four times.
Emily G. Severance, Ph.D., an assistant professor from the Stanley Division of Developmental Neurovirology at Johns Hopkins University School of Medicine, and her colleagues suggested that exposure to infectious agents, such as viruses or parasites and pathogens, during development can damage the central nervous system and trigger behavioral changes and mental illnesses in adulthood. The researchers found that men with schizophrenia or bipolar disorder were more likely to have a history of Candida albicans (C. albicans) yeast infections, while women with schizophrenia or bipolar disorder who tested positive for C. albicans performed worse on standard memory tests compared to women with no evidence of past infection.
Recent studies indicate that schizophrenia is associated with persistent systemic inflammation and neuroinflammation. Although the existing antipsychotic drugs show substantial benefits in controlling patients’ positive symptoms, they are not effective for eliminating other symptoms of schizophrenia. The role that inflammation plays in the development of schizophrenia has led researchers to investigate the use of non-steroidal and other anti-inflammatory drugs as adjunct therapy to reduce the severity and frequency of patients’ schizophrenia symptoms.
How does the immune system impact mental illness?
A study conducted by researchers from the University of Cambridge found that mental illnesses (i.e., psychosis and depression) and chronic physical illnesses (i.e., Type 2 diabetes and coronary heart disease) may share some common biological mechanisms, which may help to explain the high comorbidity between physical and mental health conditions. The researchers found that higher levels of systemic inflammation in childhood were associated with a heightened risk for developing depression and psychosis in young adulthood.
Mental illness is associated with elevated stress levels, which can also promote negative mental and physical health outcomes. People who are chronically stressed are more vulnerable to health problems due to the increased release of cortisol and other stress-related hormones, including epinephrine and endorphin, as part of the body’s fight-or-flight response, which can take a major toll on the body’s ability to fight off infection and disease. The exposure to chronic stress and early traumatic events can affect the immune system’s ability to function and fight off certain infectious agents and disease, which further increases the susceptibility for developing mental disorders such as depression later in life.
Depressive disorders are yet another mental illness that might be related to inflammation and poor immune system function. Depression affects a large percentage of the adult population in the United States and is considered to be one of the leading causes of disability worldwide. Recent studies, such as the one published by Andrew H. Miller, M.D., from Emory University School of Medicine, and Charles L. Raison, M.S., from the University of Wisconsin-Madison, suggested that inflammation and immune system dysfunction may precipitate the development of depressive disorders. With new evidence suggesting that schizophrenia may be related to problems with the immune system, it is possible that immune system dysfunction is much more involved in the development of mental illness than previously thought.
It is also possible that inflammation can underlie the development of mental illnesses such as schizophrenia, bipolar disorder and depressive disorders, although there is much to be learned regarding the relationship between the immune system and the brain. In recognition of the importance of incorporating a holistic approach to providing behavioral health treatment services, the Sovereign Health Group offers individualized and comprehensive services that incorporate aspects of physical and mental well-being for improving patients’ overall health. To find out more about Sovereign Health’s treatment programs for substance use disorders, mental illnesses such as schizophrenia, bipolar disorder and depression, and co-occurring disorders, please contact our 24/7 helpline to speak to a member of our team.
About the author
Amanda Habermann is a writer for the Sovereign Health Group. A graduate of California Lutheran University, she received her M.S. in clinical psychology with an emphasis in psychiatric rehabilitation. She brings to the team her background in research, testing and assessment, diagnosis and recovery techniques. For more information and other inquiries about this article, contact the author at firstname.lastname@example.org.