People who are hospitalized for infections may face an increased risk of dying from suicide, according to a new study that may suggest a biological basis for some suicidal behavior.
The researchers examined data in a Danish national registry, following 7.2 million people from 1980 to 2011. They found that people who were hospitalized for infections during that period had a 42 percent increased risk of dying by suicide compared with people not hospitalized for infection.
The research bolsters an idea that has been gaining more weight among psychiatrists, the hypothesis that suicide is linked to bodily inflammation.
How inflammation could affect behavior
Over the years, small studies have found a link between inflammation — which is essentially the result of the immune system going into attack mode — and suicidal behavior. A 2015 review published in the Annals of Gastroenterology found that a third to half of patients treated with drugs that spur inflammatory responses develop depression as a side effect of treatment.
But no one had really addressed the origin of this inflammation, Brundin told Live Science. In the new study, a team led by researchers at Copenhagen University Hospital turned toward infections, an obvious immune-system trigger, as a possible cause of inflammation.
The researchers used the Danish Civil Registration System to gather data on the psychiatric diagnoses, hospitalization history and cause of death for residents of Denmark who were 15 or older in 1980. This cohort of more than 7 million people was followed until December 2011.The Danish registries are an unusually detailed data source, offering detailed information on aspects of people’s lives such as unemployment, marital status and socioeconomic status, that can be difficult to gather in large studies.
The role of infections
The vast majority of people who had an infection serious enough to require hospitalization did not die by suicide. And likewise, the majority of people who did die by suicide did not have a history of serious infection. Nevertheless, after controlling for demographics, socioeconomics and other factors that might influence suicide rate, the researchers found that people who were hospitalized for infections were 42 percent more likely to die by suicide than people who were not.
“The numbers indicating an increased risk for suicide after severe infections are high, perhaps surprisingly high even for us working with this subject,” Brundin told Live Science.
There are many mechanisms that could link infections and suicide, study leader Helene Lund-Sørensen, of Mental Health Centre Copenhagen, told Live Science. The team controlled for factors like cohabitation, sex, age and the presence of chronic diseases to try to narrow their focus on psychiatric disorders, but weren’t able to account for the fact that some psychiatric disorders might go undiagnosed. There might also be self-care issues that cause people with depression and suicidal behaviors to be more likely to come down with an infection.
However, Lund-Sørensen and her colleagues wrote, the new findings fit with other results from the smaller psychiatric studies on inflammation and suicidal behavior, the researchers wrote.
Lund-Sørensen and her colleagues are planning a study to investigate whether less severe infections that don’t require hospitalization, might be linked with suicide.
There are many ways an inflammation-suicide link could affect how health care providers approach patients, Brundin said, such as increasing their focus on psychiatric symptoms when patients are in the hospital with an infectious disease. Clinical trials could attempt to eradicate chronic infections with antibiotics, Brundin said, and anti-inflammatory drugs could reduce inflammation. Currently, patients with suicidal behavior are excluded from most clinical trials, Brundin added, which gives a skewed view on how pharmaceuticals might affect them.
“Novel treatment studies in suicidal and depressive patients are highly warranted,” she said.