The immune system may play a vital role in the development of mental illness, according to new research published in the journal JAMA Psychiatry.
The study shows that children with regularly high levels of a protein released in the blood during an infection are at greater risk of developing depression and psychosis as adults.
“Our immune system acts like a thermostat, turned down low most of the time, but cranked up when we have an infection. In some people, the thermostat is always set slightly higher, behaving as if they have a persistent low level infection — these people appear to be at a higher risk of developing depression and psychosis,” said study leader Dr. Golam Khandaker of the Department of Psychiatry at the University of Cambridge.
“It’s too early to say whether this association is causal, and we are carrying out additional studies to examine this association further.”
For the study, scientists led by the University of Cambridge analyzed a sample of 4,500 individuals from the Avon Longitudinal Study of Parents and Children. They took blood samples from the participants at age nine and then followed up at age 18 to see if they had experienced any episodes of depression or psychosis.
The researchers divided the participants into three groups, depending on whether their everyday levels of the protein interleukin-6 (IL-6) were low, medium or high. They found that children in the “high” group were nearly twice as likely to have experienced depression or psychosis than those in the “low” group.
“Inflammation may be a common mechanism that influences both our physical and mental health. It is possible 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,” said senior author Dr. Peter Jones, head of the Department of Psychiatry.
People with depression and schizophrenia are known to have a much higher risk of developing heart disease and diabetes, and elevated levels of IL-6 have previously been shown to increase the risk of heart disease and type II diabetes.
Furthermore, low birth weight, a marker of abnormal fetal development, is connected to increased everyday levels of inflammatory markers as well as greater risks of heart disease, diabetes, depression, and schizophrenia in adults.
The findings could help explain why physical exercise and diet — classic ways of reducing risk of heart disease — are also found to enhance mood and lower depression. The researchers are now planning further studies to confirm whether inflammation is a common link between chronic physical and mental illness.
The research also hints at the possibility of treating mental illness with anti-inflammatory drugs. Previous research has suggested that anti-inflammatory drugs, such as aspirin, used in conjunction with antipsychotic drugs may be more effective than just the antipsychotics alone.
Source: University of Cambridge