Chronic infections and illnesses in childhood may influence mental health problems later in life, according to research from the University of Birmingham.
They found that 9-year-olds with elevated inflammatory markers were five times more likely to develop psychosis or schizophrenia.
They also had a higher risk of depression and diabetes, according to the study published in the medical journal JAMA Psychiatry.
The authors said further research could lead to preventive treatments for mental illness in the future.
The researchers used a database called the Avon Longitudinal Study of Parents and Children (ALSPAC), which began in the 1990s and has monitored thousands of people since birth.
An inflammatory marker called C-reactive protein (CRP) was measured when the participants were 9, 15 and 17 years old.
The study found a strong association between low elevated levels of CRP in 9-year-olds and later psychosis and depression, but when elevated levels were found in 15- and 17-year-olds, it was not a contributing factor.
It is thought that low-grade inflammation, which peaks at age 9, may have downstream effects on the central nervous system by altering the shape of immune cells in the brain in a process called microglial activation.
Lead author Edward Palmer said the next step is to find the triggers for the inflammation.
These may be genetic or may be due to childhood infections, anxiety, stress or trauma, all of which can cause elevated CRP.
Palmer is currently conducting another study to see whether anti-inflammatory drugs could help people with psychosis and schizophrenia.
He said understanding the role inflammation plays in mental health may be just as important as understanding its role in cancer.
He added that an increase in allergies and autoimmune diseases, as well as changes in people’s gut bacteria over time, may all be linked to this phenomenon.
