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CAMBRIDGE, England — A study on childhood insulin levels shows that the link between physical and mental illness is closer than previously thought. Researchers at the University of Cambridge reveal that persistently high insulin levels in mid-childhood are tied to the development of psychosis in adulthood.

The study also finds an increase in body mass index (BMI) when puberty kicks raises the risk of developing depression in adulthood, particularly in girls. This means that the early signs of developing physical health problems could be present long before the development of symptoms of psychosis or depression, and the relationship between physical and mental illness is more complicated than believed.

The findings spark hopes for better preventative measures and the potential for new treatments in the future.

“The general assumption in the past has been that some people with psychosis and depression might be more likely to have a poor diet and lower levels of physical exercise. So any adverse physical health problems are a result of the mental disorder, or the treatment for it,” says study lead author Dr. Benjamin Perry of Cambridge’s department of psychiatry, in a statement. “In essence, the received wisdom is that the mental disorder comes first. But we’ve found that this isn’t necessarily the case and for some individuals it may be the other way around, suggesting that physical health problems detectable from childhood might be risk factors for adult psychosis and depression.”

The team recommends that healthcare professionals carry out robust physicals of young people with symptoms of psychosis or depression to help spot and treat physical illnesses early. People with depression and psychosis can have a life expectancy of up to 20 years shorter than the general population, mostly because physical health problems like diabetes and obesity are more common among them.

Psychosis and depression in adulthood are already known to be linked with significantly higher rates of diabetes and obesity than the general population, but these links are often put down to the symptoms of the mental disorder itself.

“These findings are an important reminder that all young people presenting with mental health problems should be offered a full and comprehensive assessment of their physical health in tandem with their mental health. Intervening early is the best way to reduce the mortality gap sadly faced by people with mental disorders like depression and psychosis,” says Dr. Perry.

Tying insulin levels to mental health struggles later in life

Dr. Perry and his colleagues say that disruption to insulin levels can be detected in childhood, long before the onset of psychosis. This suggests that some people with psychosis may have an inherent susceptibility to developing diabetes. The team used a statistical method to group individuals based on similar trajectories of change in insulin levels and BMI from age one to 24. They examined how the different groups related to risks of depression and psychosis in adulthood.

About three-quarters of study participants had normal insulin levels; between 15 percent and 18 percent had insulin levels which increased gradually over adolescence and around three percent had relatively high insulin levels. This third group had a higher chance of developing psychosis later in life compared with the average group.

The researchers did not find that the group who had a persistently high BMI through childhood and adolescence had a significantly increased risk of depression in adulthood. Instead, their findings suggest that certain factors around the age of puberty that might cause the BMI to increase could be important risk factors for depression. The team did not determine what those factors might be, and future research will be required to find them. Those factors might be important targets to reduce the risk of depression.

“The next step will be to work out exactly why persistently high insulin levels from childhood increase the risk of psychosis in adulthood, and why increases in BMI around the age of puberty increase the risk of depression in adulthood. Doing so could pave the way for better preventative measures and the potential for new treatment targets,” added Dr. Perry.

The researchers caution that the risk factors are among many, genetic and environmental, and that their results do not suggest that one could predict the likelihood of developing adult mental disorders from these physical health measures alone.

The study used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a long-term population-representative birth cohort study set in western England.

The findings were published in the journal JAMA Psychiatry.

SWNS writer Laura Sharman contributed to this report.

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