Mental illness is often thought to be isolated in the brain, separated from the rest of the body by the blood brain barrier and not at all related to other physiological occurrences elsewhere in the body. This notion is falling by the wayside, however, as study after study links mental illnesses with biological manifestations throughout the body.

A recent study published in the Journal of the American Medical Association Psychiatry found that children who had higher levels of systemic inflammation were more likely to experience depression or psychosis than children with the lowest levels. The researchers studied a group of over 4,500 children who had blood samples taken at age nine and who were followed up again at age 18. Those with the highest levels of the inflammatory marker interleukin 6 (IL-6) at age nine were most likely to have experienced depression or psychosis by age 18.

Low-grade inflammation has been linked to mental illness in other studies. Some researchers think that the inflammation is a cause of the mental illness, which highlights the importance of lowering inflammation with a good diet and healthy lifestyle.

“Our immune system acts like a thermostat, turned down low most of the time, but cranked up when we have an infection,” noted Golam Khadaker, PhD. “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.”

IL-6 is usually released by the immune system in response to infection. A low level of inflammation, as detected in this study, could mean the response is to a low-level infection such as an imbalance of gut bacteria. This same low-level inflammation has been linked to a range of chronic diseases, including heart disease and diabetes.

“Inflammation may be a common mechanism that influences both our physical and mental health,” said Peter Jones, MD, PhD, lead researcher. “It is possible that early life adversity and stress lead to persistent increases 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.”