A 32-year study of 7.2 million Danish individuals suggests that there is a connection between a person’s hospitalization with an infection and his or her risk of suicide. Compared to those individuals in the study who were not hospitalized with an infection, there was a 42 percent increase in the risk of death by suicide for those who had any history of hospitalization with infections -- ranging from HIV-AIDS-related infections to sepsis.

The research, first-authored by Helene Lund-Sørensen, of Mental Health Centre Copenhagen, Denmark, was published August 10 in JAMA Psychiatry. The investigative team included 2005 Independent Investigator grantee Teodor T. Postolache, M.D. of the University of Maryland School of Medicine and the VA Rocky Mountain Mental Illness Research, Education and Clinical Center (MIRECC) for Suicide Prevention.

Their study is the largest to date to examine whether infections might be a predictor in the risk of suicide. Recent research suggests that infection and inflammation may contribute to psychiatric illness, either by attacking the tissues of the brain directly or by generating molecules that disrupt the brain’s normal functioning.

The study drew from the hospitalization and psychiatric records of people living in Denmark between 1980 and 2011. Among the 7.2 million people included in the study, there were 32,683 suicides. The analysis suggests that about 1 in 10 suicides on a population-wide level might be linked to hospitalization with infection.

Dr. Lund-Sørensen and colleagues noted that the risk of suicide rose with an increasing number of infection-related hospitalizations: a person hospitalized with infection seven or more times had three times the risk of death by suicide than those who were not hospitalized with infection.

The longer a person remained in the hospital for infection treatment also increased an individual’s suicide risk, the researchers found. These trends held even when the scientists accounted for other variables such as whether a person had been previously diagnosed with a psychiatric disorder.

The impact of infections seemed to be strongest for hospitalizations for hepatitis and HIV-related infections. Pregnancy-related infections and ear infections were not linked to a higher risk of suicide. The exact connection between infection and suicide risk—whether infection produces a direct biological cause for suicidal behavior, or whether infection is a “proxy” for another behavior or phenomenon that increases risk—should be examined further in light of this study, the researchers argue.