The immune system may play a role in mental illness, according to a recent study.

Researchers from the University of Cambridge found that Children with high everyday levels of a protein released into the blood in response to infection are at greater risk of developing depression and psychosis in adulthood.

This means that mental illness and chronic physical illness such as coronary heart disease and type 2 diabetes may share common biological mechanisms.

"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," Golam Khandaker, who led the study, said in a statement. "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, researchers collected data from about 4,500 individuals from the Avon Longitudinal Study of Parents and Children - also known as Children of the 90s - taking blood samples at age 9 and following up at age 18 to see if they had experienced episodes of depression or psychosis. The team divided the individuals into three groups, depending on whether their everyday levels of IL-6 were low, medium or high.

They found that those children in the 'high' group were nearly two times more likely to have experienced depression or psychosis than those in the 'low' group.

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 2 diabetes.

"Inflammation may be a common mechanism that influences both our physical and mental health," Peter Jones, senior author of the study, said in a statement. "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."

The research also hints at interesting ways of potentially treating illnesses such as depression: anti-inflammatory drugs. Treatment with anti-inflammatory agents leads to levels of inflammatory markers falling to normal. Previous research has suggested that anti-inflammatory drugs such as aspirin used in conjunction with antipsychotic treatments may be more effective than just the antipsychotics themselves.

The findings were recently published in JAMA Psychiatry.