People who experience depression during their youth are at increased risk of numerous illnesses and even premature death later in life, according to an extensive study conducted by researchers at the Karolinska Institute in Sweden.

Using data from Swedish national registers that contained information on all individuals born in the country between 1982 and 1996, researchers followed nearly 1.5 million individuals through 2013. Participants were between 17 and 31 years old when the study concluded. 

The researchers examined the effect of youth depression — defined as an individual receiving at least one diagnosis of depression between the ages of 5 and 19 — on the development of 69 different somatic conditions.

This study marks the first time that an investigation was conducted into youth depression using such a large set of data, according to author Marica Leone of the Karolinska Institute’s Department of Medical Epidemiology and Biostatistics. Leone said that the team of researchers pursued this line of study due to a lack of work examining youth depression, and that they were “not expecting to get such a big effect, such a big risk” from the data.

Their research, published Dec. 9 in JAMA Psychiatry, found that 2.5% of the individuals included in the analysis had a youth depression diagnosis, totaling 37,185 patients. The researchers estimated hazard ratios, or the probability of a situation occurring, during their analysis and found that 66 of the 69 somatic diagnoses had strong associations with youth depression. Individuals who suffered from youth depression were shown to be about eight times as likely to develop sleep disorders, for example, and were about six times as likely to develop viral hepatitis. 

Notably, individuals who received a depression diagnosis during childhood were nearly six times as likely to experience premature death, or what the study refers to as “all-cause mortality.” Youth depression sufferers were also 14.6 times as likely to die by suicide than those without a childhood depressive episode. 

There were also some differences between sexes highlighted in the study. Women who suffered from youth depression were found to have a significantly higher incidence of self-harm, being 14 times more likely to engage in it, and also had higher risks of urinary and respiratory infections. Men who had a youth depression diagnosis were noted as having higher risks of obesity and thyroid gland issues.

Children are at different risks of developing depressive symptoms based on the socioeconomic status of their family, as well as its history of psychiatric illnesses, Leone said. For kids, having an adult in their lives, such as an educator or family member, take action and bring awareness to the issue may be a way to mitigate the development of depression.

Leone said that this study highlights how further research is necessary to understand the true impact that depressive symptoms can have on children and the nature of the link between mental and physical health.

“We can’t prove with our study that depression is … causing you to get disorders, but we know there is an association,” Leone said. “So we need to understand what’s going on — is that a direct link? Or is there something else that increases the kids’ risk of getting both depression and somatic conditions? It might be driven by something else, but we need more research.”

The other goal of this particular study is to shine a bigger light on the problem of youth depression itself, which Leone said is an often-overlooked issue.

“Most people still don’t recognize that it’s a problem, and believe that depression is something that just happens in adulthood,” Leone said. “That is not the case … We hope that in the future, this young population will receive the attention they need, as well as earlier and better care going on and going forward.”

The article, “Association of Youth Depression With Subsequent Somatic Diseases and Premature Death,” was published on Dec. 9, 2020 in JAMA Psychiatry. It was authored by Marica Leone of the Karolinska Institute’s Department of Medical Epidemiology and Biostatistics and of the Janssen Pharmaceutical Companies, Ralf Kuja-Halkola of the Karolinska Institute, Amy Leval of Janssen Pharmaceutical Companies, and Sarah Bergen of the Karolinska Institutet.