Researchers used a database started in the 90s called the Avon Longitudinal Study of Parents and Children (Alspac) which has monitored thousands of people since birth.
An inflammatory marker known as c-reactive protein (CRP) was measured when participants were nine, 15, and 17 years of age.
The study found a strong connection between low-level raised CRP when children were nine, with later psychosis and depression – but it was not a factor when it was found in 15 or 17 year olds.
It is thought that low-grade inflammation, which peaks at nine years of age, may have an effect downstream on the central nervous system, as inflammation causes brain immune cells to change shape in a process called microglia activation.
Lead author, Edward Palmer, said the next stage was to find the triggers for the inflammation.
They could be genetic or due to childhood infection or anxiety, stress and trauma which can all cause a rise in CRP.
Mr Palmer is now conducting another study to see if anti-inflammatories could help patients with psychosis and schizophrenia.
He said understanding the role of inflammation in mental health could be as important as it was in understanding its role in cancer in the 70s.
He added that an increase in allergies and autoimmune disease and changes to the bacteria in the human gut over time could all be associated with this phenomenon.
Sarah Carter is a health and wellness expert residing in the UK. With a background in healthcare, she offers evidence-based advice on fitness, nutrition, and mental well-being, promoting healthier living for readers.