The Immune System May Influence the Development of Mental Illness
Cambridge led a team of scientists as they followed a group of 4,500 individuals from age 9 to age 18. The subjects were divided into three groups depending on whether they had low, medium or high daily levels of a certain protein. This protein, known as interleukin-6 (IL-6), is a strong marker of infection, but is also present in smaller but varying levels at all times in the human body.
Blood samples were gathered from each subject at age 9, and the researchers followed up with each subject at age 18 to determine their history of depression and psychosis. They found that the children who had been placed in the group with high daily levels of IL-6 were almost twice more likely to have a history of either depression or psychosis than those who had been classified as having low daily levels of IL-6.
Physical Illness and Psychiatric Illness May Be Connected
This is not the first time that the IL-6 protein has been connected to a higher risk of illness. Previous research has drawn a connection between high daily levels of IL-6 and a greater incidence of two chronic physical illnesses—type II diabetes and heart disease.
This suggests that there may be common mechanisms at work in the development of physical illness and the development of mental illness. Senior author of the study Peter Jones, head professor of the Cambridge Department of Psychiatry, hypothesizes that “early life adversity and stress lead to persistent increase in levels of IL-6 and other inflammatory markers in our body, which, in turn, increase the risk of a number of chronic physical and mental illness.”
Common Causes and Possible Common Solutions
This connection suggests new explanations for why certain activities, such as physical exercise and changes in diet, are known to help alleviate symptoms of such apparently different illnesses as heart disease and depression.
The link also suggests possible new methods of treating or even preventing mental illness. Anti-inflammatory drugs such as aspirin and ibuprofen are known to reduce daily levels of inflammatory markers like IL-6 to a range that is considered normal. This raises the possibility that this type of drug could be used to treat mental illness in conjunction with other medication or with therapy, or even that anti-inflammatory drugs could be used preventatively to bring inflammatory markers in people with high daily levels down to normal levels. This could help to prevent depression or psychosis from ever developing in these individuals.
There is even previous research that supports this idea; a study published in 2010 in the Journal of Clinical Psychiatry found that treating schizophrenic patients with aspirin in addition to anti-psychotic drugs was more effective than treating them with antipsychotics alone. An additional study that is currently underway is testing whether minocycline, an antibiotic used to treat acne, can treat a variety of symptoms associated with schizophrenia, including social withdrawal and apathy.
Further research is needed to confirm the hypothesis that inflammation has more than a casual association with the development of mental illness, and that it is a common link between mental illness and chronic physical illness. One of the main puzzles remaining to be solved is how inflammatory markers that cannot pass the “blood-brain” barrier could be able to influence the brain.
The University of Cambridge study was published on August 13, 2014 in the journal JAMA Psychiatry.